What size deep cycle battery?

[Stereo]

Please forgive this post. The answer I seek seems to be embedded too deeply in previous posts to find 'cause I've been searching the forum for over an hour without luck.

I need a new deep cycle battery for the Skamper pop-top I recently acquired and am fixing up. What amperage should I get? I'm going to change out the three interior area lights to LED and would like to power a CD player. I don't have a frig but may want to add one sometime in the future. My heater and burners run on propane so no draw there. There are clearance lights that currently come on whenever the interior lights are turned on when plugged into 120V but I'm going to separate those circuits. I'll typically only be out for 2-3 days at a time. I do plan to add a solar recharge set-up sometime in the future.

What size battery do I need?

Thanks for the help!

 

[dwh]

Please forgive this post. The answer I seek seems to be embedded too deeply in previous posts to find 'cause I've been searching the forum for over an hour without luck.

I need a new deep cycle battery for the Skamper pop-top I recently acquired and am fixing up. What amperage should I get? I'm going to change out the three interior area lights to LED and would like to power a CD player. I don't have a frig but may want to add one sometime in the future. My heater and burners run on propane so no draw there. There are clearance lights that currently come on whenever the interior lights are turned on when plugged into 120V but I'm going to separate those circuits. I'll typically only be out for 2-3 days at a time. I do plan to add a solar recharge set-up sometime in the future.

What size battery do I need?

Thanks for the help!

My camper van has a 100ah flooded -deep cycle- aux battery under the hood. It charges via split-charge relay when the engine is running, and via small generator and battery charger when camped. It's old and it's been rode hard and put away wet (i.e., drained well below 50% and then not properly recharged in a timely fashion).

Running just an exhaust fan on the overhead vent, an oscillating fan inside, one or two lights (1141s, not LEDs) and recharging my netbook and some AA and AAA batteries it goes a good three days before it's pretty much dead. It did about twice that when it was new 2 years ago so the frequent abuse has reduced it's capacity by nearly 50%, so I suppose now it's a 50ah battery instead of a 100ah battery.

I plan to replace the charger with a good 2-stage charger (Samlex SEC-1215a) and replace the battery with another new 100ah cheapo flooded deep cycle.

I buy cheap batteries because I know I'm going to abuse them, but I do NOT buy RV/Marine batteries for aux use. I buy deep cycle batteries.

I haven't bothered with solar because I park in the shade when I can, and when I can't I have a surplus parachute that covers the entire vehicle and serves as a good sized awning on all 4 sides.

Batteries are basically "watts per pound" so whatever size battery fits - Group 27, Group 31, etc. The battery I have now is basically like this:

http://www.cloudelectric.com/product_p/ba-27dc36.htm

But without the label. There is a battery shop in my area that often gets their hands on batches of "no label" and/or "scratch and dent" batteries. I paid $45 for the one I have now.

 

[windsock]

What size battery do I need?

Thanks for the help!

Go visit this website for some ideas on sizing. Dan did a small camper refit for a fishing camper/pop-top... they're just up the road from you in Boulder, they're in Fort Collins.

 

[Stereo]

Wire size? Venting? Grounding?

Thank you for all the information. Great link for a basic understanding of power and solar! The article led to more questions beyond what size battery to get.

My old Skamper has a built-in inverter. The former owner connected the deep cycle battery to the inverter panel with stranded lamp wire. Clearly, that's not appropriate, but other than saying to use "thick and flexible" wire for that connection, the article did not specify size. What gauge wire should I use?

One illustration of wiring off or to a battery suggested the battery should be grounded. Is that necessary? If mine's inside the camper, how might I ground it?

Other articles talk about the need to vent the battery. Is that necessary? I'm not keen on punching more holes in the camper but I also want to be safe. I might be able to put it outside the camper and feed the wiring inside, but others have talked about that making the battery more vulnerable to theft.

 

[dwh]

My old Skamper has a built-in inverter. The former owner connected the deep cycle battery to the inverter panel with stranded lamp wire. Clearly, that's not appropriate, but other than saying to use "thick and flexible" wire for that connection, the article did not specify size. What gauge wire should I use?

Inverter, or converter? Inverter changes 12v DC to 120v AC. Converter changes 120v AC to 12v DC (and also usually does a bit of battery charging).

The wire size is determined by the amount of load on the wire (in amps), and the length of the wire. Wire has a rating of the maximum amps that it can carry, but also voltage drops over distance, so a long run of wire might need to go up a size or two in order to carry the amps without dropping the volts too much.

Assuming we're actually talking about an inverter, the first step is to figure out how much it draws from the battery. Let's say it's a 1000w inverter that can briefly handle a surge load up to 1500w. We need wire that can handle the larger load - 1500w.

Now watts is watts. The inverter needs to supply 1500w @ 120v on the output, and so it need to draw 1500w @ 12v on the input. Now we do the most basic of electrical math: watts / volts = amps

1500w / 12v = 125a

So we need wire from battery to inverter which can handle a 125a load. Now we consult a wire gauge chart:

http://www.powerstream.com/Wire_Size.htm

We're doing power transmission ("chassis wiring" does NOT mean vehicle chassis - it means machine chassis - i.e., in an enclosed space), so we look in that column and we see that we need wire size 0, which can handle up to 150a. Now we know what size of "big, fat" wire we need to feed that inverter. That size would be fine for a short run say up to 6'. For a longer run, we might have to go up to a larger size to keep the voltage from dropping too much.


(Note that this is 10 times the size of wire we'll need on the output side of the inverter because the output is at 120v. Doing the same math formula:

1500w / 120v = 12.5a

We only need wire on the output side capable of handling 12.5a. 14 ga. wire and a 15a breaker or fuse would handle that nicely.)

One illustration of wiring off or to a battery suggested the battery should be grounded. Is that necessary? If mine's inside the camper, how might I ground it?

Vehicles aren't actually grounded - they aren't connected to the planet - nor should they be unless they are something like a truck mounted generator being used to power a building, or like a boat or RV being fed from shore power.

In a vehicle, "ground" usually means "to connect to the frame". You should have both a positive and a negative wire from battery to inverter, and another pair from charger to battery. But yes, it's best if there is -also- a wire from battery to frame so that if any positive wires get loose and happen to touch the frame, it will provide a path back so that the fuse can blow for safety.

Other articles talk about the need to vent the battery. Is that necessary? I'm not keen on punching more holes in the camper but I also want to be safe. I might be able to put it outside the camper and feed the wiring inside, but others have talked about that making the battery more vulnerable to theft.

If it's a flooded battery then yes, it's absolutely required to be vented. Flooded batteries offgas hydrogen when they are being charged. I don't know if you've ever seen hydrogen burn...but it burns so fast that it fits the description of "explosion". And it lights up pretty easy too.

You DO NOT want hydrogen venting into your living space.

Sealed batteries, which might be a flooded (liquid electrolyte), AGM (electrolyte absorbed into fiberglass mats), or Gel (jellied electrolyte) don't offgas hydrogen - unless they are overcharged and the sealing valve pops to relieve pressure. Then they are no different and they will vent hydrogen when being charged. Technically, it's best to have them in a vented space as well - though often people don't do that. They can get away with it as long as they make certain they don't overcharge the battery and pop the valve.

 

[tanglefoot]

My parents and I just use the regular deep-cycle batteries off the rack at Walmart. They're cost effective and very good with their warrantees.

If your furnace is an RV type (built-in with vents to the outside), it has an electric blower that uses a fair bit of electrical current.

Older and simpler propane fridges can run on propane without any electricity. Many more modern ones have electronic circuitry and air circulation that uses electrical current along with the propane (LED lights on the front panel are usually a give-away). These electronically-controlled fridges make it tough to maintain battery charge--they're always drawing current.

My parents have an isolator connected between the truck battery and camper battery. It connects the two when the engine's running to charge the camper battery and then disconnects them when the engine's stopped. That way the camper electrical use doesn't affect the ability to start the engine.

My camper and truck electrical systems are completely independent and there's a small (10-watt) solar charger on the camper. I don't have a fridge or furnace so the camper draw is pretty low. I like the solar-charge because it keeps the camper battery topped-off while it's parked outside. My parents have to hook up a separate charger because driving often doesn't charge the camper battery all the way and then it gradually discharges while it's parked.

If you have a converter, you likely have a battery compartment that's vented to the outside. I have also seen setups that have the camper battery stored between the bed and the camper--that's a vented location. Mine is stored inside the under-counter cabinets and there is a vent in the back camper wall to vent the cabinet area.

Wow--great write-up, dwh

Eric

 

[Stereo]

FANTASTIC information dwh. Not only did I get my answer, I got a thorough education too. You're right. It's a converter, not an inverter. The faceplate was partially painted over so I could only read "...verter" and now I know what's what. I'm fully versed in 120/240 house wiring but not 12v.

Thanks, Tanglewood, for the reminder about the heater fan. I forgot about that electrical feature. I'll definitely add it to my calculations. I definitely want to hook up a solar charger too so any details you care to share would be much appreciated.

I installed my Ride Rite air bags today :wings:and will post my experience with pics later.

THANK YOU.

 

[dwh]

Older converters are basically just constant voltage power supplies which can hold their rated voltage up to a certain load of amps. So say the converter puts out 12.6v 30a - then it will hold 12.6v at any load up to 30a - a load higher than 30a would start to pull the voltage down if the unit didn't overload and shut down.

Pretty similar to a regular old automotive battery charger. As long as the converter holds the bus voltage to 12.6v, then if the battery is below that voltage, it will slowly absorb power until it reaches equilibrium with the bus voltage. That's why they are often referred to as "converter/chargers".

So the converter not only supplies power to whatever 12v loads are connected, it also slowly recharges the battery up to 12.6v.


What you likely have is an old MagneTek power center. The 120v shore power comes in to it, and it passes that through to the 120v outlets in the camper. It also taps off the 120v to feed a built-in converter to supply 12v.

The problem with those old converters is that 12.6v isn't really enough for a modern battery. Most modern batteries need to be pushed up above 14v and held there a while to be truly fully charged. A smart charger will do that, and then once the battery stops absorbing power it will drop back to a "float" voltage, which these days is usually between 13.2v and 13.6v depending on the charger. The older converters were by no means smart.

The second problem, is that that old converter probably has a pretty low amperage rating. I.e., it might only supply 9a to the 12v bus and that's not much. The old Shumacher battery charger which is hard wired in to my camper puts out 12.8v and up to 10a and while it will eventually charge my battery up to 12.8v - it takes around 12 hours if the battery is really low.

That is why I'll be replacing it with a modern multi-stage charger. Not only will it still function to supply 15a to the bus for loads (I don't have many), but it will do a much better job of charging the battery and my generator run-time should be half what it is now.


If you add solar, then a decent solar charge controller, such a Morningstar Sunsaver, will be a multi-stage charger and will get the battery properly charged up to modern voltage specs.

IF there is enough watts of solar panel and IF there is good direct sun on the panel.

In that case, you could still use the ol' MagneTek if 9a (or whatever its rating is) is enough to supply your loads. It will only get the battery up to 12.6v, but the solar will override that when there is enough sun and push the battery the rest of the way up.

 

[bob91yj]

For me a maintenance free battey that was leak proof was needed. My house battery is in the front of the truck bed between the camper and the truck bed, complete PITA to get to. I went with an Optima, it has met my needs.

 

[Stereo]

Still fuzzy.

DWH: You are close to dead-on, only my output is even lower. Tonight, with a flashlight, I was able to read more through the paint. The converter is a Brand ?, Model CS506 with output of 12.5 VDC and only 6 amp.

I understand that the converter converts 120V to 12V to power my 12V stuff. And I understand your explanation about the output from the converter not being enough to fully charge a modern-day battery. But I don't yet understand how my load gets supplied. If the converter only puts out 6 amp, and according to the bus bar, the converter uses 8 amps, there would not be enough output to power andything else.

Original loads appear to be Converter - 8A and Clearance lights - 8A. I think a previous owner did some retrofitting and added a water pump, unknown amps, and 3 cabin lights with 1141 bulbs, 12V 1.44 amps each. My memory now tells me I don't have a blower in the heater (and I don't see any fan blades). If I had a frig, the panel claims it would draw 15A but I don't know if that's typical of today's frigs. I could also use propane for the frig. I'd also like to run a radio/CD or a laptop.

I'm trying to understand the wiring. The bus bar has two sides, bridged at some locations by fuses. The old defunct battery was wired to the right side and the ground with lamp wire. The wires from the converter come in on the left and I'm assuming the other wires on the left - that aren't going to the ground - are going out to the stuff they power. There is one wire that connects the left and right sides. Does power from the battery come in on the right, pass to the left side, then power the stuff from that side of the bus directly?



ALSO, please double check me on calculating battery size. If I'm figuring it right, if I were to get a 105A-hrs battery, limit it's rundown to 50%, i.e. 52.5 amp-hours, I could run 1 light (1.44 amps) and 1 CD player (13W divided by 12V = 1.08 amps) for almost 21 hours (52.5 divided by 2.52 amps). Am I doing the math correctly?

On the load calculation, I'm assuming the converter doesn't pull amps when I'm running off the battery. Am I right?

Based on the wiring chart at your link, do I need to attach the battery to the bus with 0-size wire? Is that different than 0-sized wire for 120V systems, 'cause that would be HUGE.

Thanks for your help and patience as I try to understand the 12V system.

 

[Stereo]

For me a maintenance free battey that was leak proof was needed. My house battery is in the front of the truck bed between the camper and the truck bed, complete PITA to get to. I went with an Optima, it has met my needs.

Are you saying that because it was a PITA to get to the battery when it was outside, you wanted to put one inside so you went with a sealed battery? If not, why was a maintenance-free battery needed?

 

[dwh]

DWH: You are close to dead-on, only my output is even lower. Tonight, with a flashlight, I was able to read more through the paint. The converter is a Brand ?, Model CS506 with output of 12.5 VDC and only 6 amp.

Ouch.

I understand that the converter converts 120V to 12V to power my 12V stuff. And I understand your explanation about the output from the converter not being enough to fully charge a modern-day battery. But I don't yet understand how my load gets supplied. If the converter only puts out 6 amp, and according to the bus bar, the converter uses 8 amps, there would not be enough output to power andything else.

My guess would be that that 8a converter fuse is incoming to supply the bus bar, not outgoing (i.e., it's not a load). The converter gets its power from the 120v that supplies it.

Original loads appear to be Converter - 8A and Clearance lights - 8A.

It's possible that the clearance lights are wired so that the vehicle's running light circuit energizes a relay in the trailer to turn on the trailer's clearance lights, and that the trailer's clearance lights get power from the trailer battery when the relay is energized. They might have done it that way if the trailer's clearance lights are a heavy enough load that might blow the running lights fuse in the tow vehicle.* (see below)

I think a previous owner did some retrofitting and added a water pump, unknown amps

Sureflo Classic is 7a max while running.

and 3 cabin lights with 1141 bulbs, 12V 1.44 amps each. My memory now tells me I don't have a blower in the heater (and I don't see any fan blades).

What make/model is the heater? If it's a Surburban that has a chrome input/output fitting on the outside of the camper it'll have a fan in it.

If I had a frig, the panel claims it would draw 15A but I don't know if that's typical of today's frigs. I could also use propane for the frig.

My camper has a Norcold 323 which is a 3-way. Running on 12v it draws 11.7a...horrible. I run it on propane always. On low it'll run 5-6 weeks from a 5g tank, and that includes cooking 3 squares a day.

I'd also like to run a radio/CD or a laptop.

Not sure about the radio, but laptops usually draw 30-60w depending on the size. My Acer ZA3 netbook draws 9w in power save and 13w when charging its battery.

I'm trying to understand the wiring. The bus bar has two sides, bridged at some locations by fuses. The old defunct battery was wired to the right side and the ground with lamp wire. The wires from the converter come in on the left and I'm assuming the other wires on the left - that aren't going to the ground - are going out to the stuff they power. There is one wire that connects the left and right sides. Does power from the battery come in on the right, pass to the left side, then power the stuff from that side of the bus directly?

View attachment 61633

Well, lemme see...

Okay, so first the very top terminal screw is a common (shared) negative. One of the lamp cord wires (with the black tape) from the battery goes to that, and the other lamp cord wire appears to go to the bottom fuse on the fuse block. Then, there is a wire from the left side of the bottom fuse, up and over to supply the little bus bar on the top right of the fuse block.

Also supplying that bus bar, is an incoming (red?) wire from the converter, which feeds the bus bar through a fuse.

The only load I see coming off that bus bar is the orange wire to who knows what? Lights? Water pump? Both maybe. There is also the fridge fuse (top on the bus bar) and a spare (3rd down on the bus bar) both unused.

*Then, there is the 5th fuse down, which is freaky. It has a grey wire on the right side, and appears to have a blue and a white on the left side. The freaky thing is that the blue wire is connected to the negative terminal at the top - but that *can't* be right...so the blue wire must not actually connect to that negative terminal...it probably just looks like it does and disappears down behind the fuse block.

If that blue wire actually DOES connect to the fuse AND the negative terminal, then they are doing something freaky and fusing a negative. I don't see why they'd do that, unless they did some hack to a relay to run the clearance lights. If they did, they did it wrong.

ALSO, please double check me on calculating battery size. If I'm figuring it right, if I were to get a 105A-hrs battery, limit it's rundown to 50%, i.e. 52.5 amp-hours, I could run 1 light (1.44 amps) and 1 CD player (13W divided by 12V = 1.08 amps) for almost 21 hours (52.5 divided by 2.52 amps). Am I doing the math correctly?

Yup, you're doing it right. It's a sliding scale though - the heavier the load, the quicker the battery drains. That's why deep cycle batteries are rated at various different discharge rates. A battery might supply 100ah at the 20hr rate, but supply 150ah at the 40hr rate. It's called the Peukert Effect.

http://en.wikipedia.org/wiki/Peukert's_law

On the load calculation, I'm assuming the converter doesn't pull amps when I'm running off the battery. Am I right?

Yes, but it also doesn't pull amps when it has 120v feeding it - its entire purpose is to supply power TO the bus. Can't do both at once.

Based on the wiring chart at your link, do I need to attach the battery to the bus with 0-size wire? Is that different than 0-sized wire for 120V systems, 'cause that would be HUGE.

No, that example of using #0 wire was for feeding a 1500w inverter FROM the battery. For feeding charge current TO the battery, you need wire sized according to what the charger puts out and the distance from the battery. For the piddling 6a that converter puts out, you could get by with just about anything - even lamp cord.

When I install the 15a Samlex charger in my camper, I'll be using #10 wire - not because of the amps, but because the wire will be about 10' long and so there will be some voltage drop. If I used #14 or #12, either of which could handle 15a, there would be too much voltage drop.

Thanks for your help and patience as I try to understand the 12V system.

No worries.



You should dump that converter and get a good one like an Iota or a Samlex. Running that thing you have now to charge a modern battery is a recipe for short battery life.

A 15a charger is enough for a single 100ah battery, Run at least #10 wire from the converter to that fuse block and use a 20a fuse to feed the bus bar.

Then run #10 from the battery to that unused (3rd down) fuse position and use a 30a fuse to feed the bus bar. That'll get rid of that cheezy "up and over" wire.

Of course, also use #10 for the negative connections from the converter/charger and the battery to the common negative terminal.

I'd hold that fridge fuse spot in case I needed it. My little Norcold 323 is a stupid fridge - no control board or thermostat - so when it's on propane, it doesn't need any power at all. Any other propane fridge will have a control board that will need some power at all times - though not much if it's running on propane. So you'd need that fuse slot, though you might not need a 15a fuse.

If you went with a 12v fridge, then you'd also need that fuse slot.

 

[Stereo]

Back to Kindergarden

DWH, I REALLY appreciate the time you're taking to give me such detailed information. I'll be checking into your questions tonight, but I do want to bring my understanding back to the very, very basic level. Please correct me if I'm wrong on any of this.

When plugged in to shore power, I have a 120v outlet that's fed directly from shore power so I can plug anything into that that I could in a 120v outlet in my home. In addition, shore power feeds into my converter which then converts 120v to 12v and feeds my 12v fixtures, which at this point, only includes my lights. Good thing, because I can only draw 6 amps off that converter.

When NOT plugged into shore power and using my battery, I have 100 amps capacity (assuming a 100 ah battery). But how long I can draw on the battery depends on the discharge rating of the battery and the size of the load. I have to watch that I don't draw down the battery beyond 50% for best battery life.

If I'm only gone for a weekend and won't need more than 50% of the capacity of my battery over that time, I can leave with a battery I've charged up on a charger at home and don't need to worry about recharging it.

If I'm on an extended trip and will need to keep charging the battery, if I have access to shore power, my converter can assist with the recharge but to an insufficient degree but can be supplemented by an adequately sized solar panel and enough sun.

If I do have access to shore power, given that I have a 120v outlet fed directly off shore power (i.e. not through the converter), could I just bring along a separate battery charger? I guess the question is how long those chargers take to recharge a battery.

I've read that there's also the possibility of charging the pop-top battery off the vehicle's battery (assuming the correct wiring) while driving though I understand it takes a lot of miles to do the job.

Regarding the wiring of the battery: The existing set-up only had the lamp wire running between the battery and the panel. There were no wires from the converter to the battery. Do I need a second set? i.e. To power my 12v lighting (and possible future 12v appliances) off the battery, I need to run a positive and negative #10 wire (assuming a 100ah battery and short run) from the battery to the bus bar. Correct?

Then, if I understand you correctly, if I want the converter to send (6 amps) power to the battery to help charge it when I have shore power, I need (small gauge) wiring from the converter to the battery, but is this wiring direct, or does it go through the bus bar? I have your description of the proper way to wire a new converter, but I'm confused about the direction of power as it relates to the bus bar. In my mind, the bus bar receives power either from the battery OR the converter to power the 12v fixtures. If wiring goes from the converter into the bus bar, how does the bus bar know when power is flowing in to the battery, or out from the battery?

Things I will do soon:
-Check that the "blue" wire isn't hooked up in a funky/unsafe way. (Note that there is no wiring between my truck and the pop-top.)
-Check my heater for a fan. (My pop-top was built in the '80's)

AGAIN, many, many thanks for all the information. Hopefully, these are the end of my questions on this topic.

 

[dwh]

When plugged in to shore power, I have a 120v outlet that's fed directly from shore power so I can plug anything into that that I could in a 120v outlet in my home.

Yes.

In addition, shore power feeds into my converter

Maybe. If it was a "power center" then yes. The alternative is that the converter has a power plug and is plugged into one of the 120v outlets that is powered by shore power. Or, there could be a breaker box, and the power converter is wired into a breaker.

which then converts 120v to 12v and feeds my 12v fixtures, which at this point, only includes my lights. Good thing, because I can only draw 6 amps off that converter.

Yes - and also since it is supplying 12.5v to the bus, if there are any amps left over after supplying the loads, some power will flow toward the battery until the battery gets up to 12.5v.

When NOT plugged into shore power and using my battery, I have 100 amps capacity (assuming a 100 ah battery). But how long I can draw on the battery depends on the discharge rating of the battery and the size of the load. I have to watch that I don't draw down the battery beyond 50% for best battery life.

Correct on both counts.

If I'm only gone for a weekend and won't need more than 50% of the capacity of my battery over that time, I can leave with a battery I've charged up on a charger at home and don't need to worry about recharging it.

Correct.

If I'm on an extended trip and will need to keep charging the battery, if I have access to shore power, my converter can assist with the recharge but to an insufficient degree but can be supplemented by an adequately sized solar panel and enough sun.

Yes.

If I do have access to shore power, given that I have a 120v outlet fed directly off shore power (i.e. not through the converter), could I just bring along a separate battery charger? I guess the question is how long those chargers take to recharge a battery.

Yes. You can carry along another battery charger and run it off the shore power (or a plug in the trailer when the trailer is connected to shore power).

If you had something like a 15a Iota, and a 100ah battery half depleted you would need to replace 50ah. But batteries and charging are not 100% efficient, so really you'd need to supply more like 60ah in order to get the battery back up by 50.

The majority of that would take place in about 4 hours, at which point the battery would be close to 90% full. That last 10% will take anywhere from 4-8 hours more.

A 10a constant voltage charger like my old Shumacher would take 8-12 hours to get it up to 12.8v.

I've read that there's also the possibility of charging the pop-top battery off the vehicle's battery (assuming the correct wiring) while driving though I understand it takes a lot of miles to do the job.

Yes. There are two types of battery charger - Constant Voltage, and Constant Current. A constant voltage charger just holds the voltage and allows the battery to absorb however many amps happen to overcome the battery's resistance. A constant current charger will crank up the voltage until it sees the requisite amount of amps flowing.

My old Shumacher is a constant voltage charger (as is your converter, and a truck's voltage regulated charging system). This is why on my charger's amp meter, I see like 1a for a while when the battery is really low, and as the battery voltage rises I might see 6a or 7a on the amp meter, and as the battery gets full it drops back down again.

A multi-stage charger like the Iota is both. It will go into constant current mode (bulk stage) to pump the full 15a into the battery until the batteryy voltage gets to the set point, then it switches into constant voltage mode and just holds the voltage there (float stage).

Constant voltage chargers take a lot longer to charge the battery.

Regarding the wiring of the battery: The existing set-up only had the lamp wire running between the battery and the panel. There were no wires from the converter to the battery. Do I need a second set? i.e. To power my 12v lighting (and possible future 12v appliances) off the battery, I need to run a positive and negative #10 wire (assuming a 100ah battery and short run) from the battery to the bus bar. Correct?

Think of it like an air compressor. The battery is the tank, the fuse block is a distribution manifold. The converter is the pump. It doesn't really matter if the pump is connected directly to the tank or if it's connected to the manifold - as long as there is sufficient pressure (voltage) the air will flow from the pump to the tank and the tank will fill up.

But yes, you should have wire larger than lamp wire from the battery to fuse block. #10 with a 30a fuse will probably be enough. My truck has a #8 wire feeding through a 50a breaker to supply the aux fuse block. It was there when I got the truck, and hasn't had a problem.

One advantage of they way it is now, is that there is a fuse in the line between the battery and the bus bar, and another fuse in the line between the converter and the bus bar. Both fuses are needed anyway, so the way it is now works. It just needs larger wire.

And, since there is a spare fuse slot, you can run the battery to that to feed the bus bar through a fuse, without needing that up and over jumper that there's now.

Then, if I understand you correctly, if I want the converter to send (6 amps) power to the battery to help charge it when I have shore power, I need (small gauge) wiring from the converter to the battery, but is this wiring direct, or does it go through the bus bar? I have your description of the proper way to wire a new converter, but I'm confused about the direction of power as it relates to the bus bar. In my mind, the bus bar receives power either from the battery OR the converter to power the 12v fixtures. If wiring goes from the converter into the bus bar, how does the bus bar know when power is flowing in to the battery, or out from the battery?

Yea, back to the air compressor analogy. The entire system is the "air system" (a.k.a., "the bus"). If the pump is running (converter on) it will hold the pressure at 12.5 psi (voltage). If the tank (battery) pressure (voltage) is lower than 12.5 psi (volts), then air (current) will flow into the tank until the tank reaches 12.5 psi (volts). At that point, everything is equal pressure and so nothing flows.

If the pump is on, then it will hold the pressure up to 12.5 psi, but it can only do 6 cfm (amps). Now say you run an air gun (load) from the system (bus). If the drain (load) exceed 6 cfm (amps), then the pressure (voltage) in the system (bus) will drop, and air will flow from the tank (battery). As soon as the load is turned off, then the pump will bring the entire system (bus) back up to 12.5 psi (volts).

If the pump is off, then any loads (your air gun) will draw down the pressure (voltage) in the system (bus). As the system pressure (bus voltage) drops, air (current) will flow from the tank (battery) to keep the pressure equalized (keep the bus voltage up).



So which way does power flow? From the higher voltage toward the lower voltage. Voltage is like pressure. Amperage is like cubic feet per minute.

If the converter is putting out 12.5v to the bus, and the battery voltage is less than 12.5v, then the pressure differential will cause some current to flow toward the battery until the voltage is equalized.

If you turn on a load, then current will flow from the bus to the load, and that will drop the bus voltage, and so current will flow from the converter to the bus. Unless the load is greater than 6a, in which case current will flow from both the converter AND the battery toward the bus. As soon as you turn off the load, then the converter will bring the bus voltage back up to 12.5v and if the battery got down lower than that while supplying the load, some current will flow toward the battery until the voltage is once again equalized.

Things I will do soon:
-Check that the "blue" wire isn't hooked up in a funky/unsafe way. (Note that there is no wiring between my truck and the pop-top.)

No? Then how are the clearance lights turned on and off? Manually? What about brake lights?

-Check my heater for a fan. (My pop-top was built in the '80's)

AGAIN, many, many thanks for all the information. Hopefully, these are the end of my questions on this topic.

No worries. Docendo discimus.

 

[MakersTeleMark]

I highly suggest getting a modern converter, and re-wire everything. Now is the perfect time to do it. Dealing with legacy systems is a PITB. At this point, your current system requirements are really simple, so over-design a new panel now and you'll be set to add to it as things get more complex down the road. If you ever pass through central colorado, I can walk you through it all and show you how I chose to do it in my camper.