Electrical help please - lost and confused - calculating battery needs for uses

[Chorky]

Ok all, so I've done a ton of reading for, well a long time, and as parts of my build get closer I'm becoming no more knowledgeable as I had hoped for electrical systems. I'm no newbie to electrical theory, but for some reason this particular bit is getting the best of me. I am trying to ultimately figure out the electrical 'system' I need to either 1) reasonably power all the items I plan to have, or 2) realize certain constraints with the amount of battery space/weight I have available, and build a system around that to suit it.... if that makes sense.

The items in consideration:
12v fridge (as of now it's a snomaster LP66 dual bin)
Standard water pump
2 maxx fans
Diesel air heater
Diesel water heater
12v lights inside (maybe 4 total?)
12v lights outside (3, one on each side)
600w inverter (maybe more?) (looking at option from zamp solar to charge computer, batteries, phones, GPS, etc...)
Camper 'radio' - like a normal car radio - might not actually happen
12v heating pad for water tank to prevent freezing in sub-zero temps
12v heating pad in water heater compartment to prevent freezing, so water heater is not always running
12v heating pad for truck oil pan (likely only used for an hour or two prior to starting and moving in sub-zero temps to prolong engine life)
possible additional diesel coolant heater for engine
Twin Viair compressors (not part of the 'camper' but part of the truck's 'system' and probably wired to the 'camper' batteries - likely only used when truck is running as it's a 44a draw and 100% duty cycle)
Additional water draw pump (not necessarly part of the 'camper' but part of the truck's 'system' - likely only used when the truck is running)

So situation 1:
Lets say I have the items above. And lets say that I know their amp pull per a 24 hour period based on guestimated usage, and can multiply that by 3 for a 3 day period (I don't have the numbers off hand but can research and find them probably). How do I:
a) find the total ah needed for a 24/48/72 hour window
b) find out how much time the batteries would need to fully charge given a x rated max alternator, and an assumed x amount of amps going to the actual batteries
c) combine this situation with potential future solar panels to calculate potential charge rate and see if that charge rate is reasonably acceptable enough to make the solar system worth it
d) run these numbers against a specified (unknown and undecided on just yet) battery set to see the expected calculated performances - maybe something like 2 of these http://lifelinebatteries.com/products/marine-batteries/gpl-31xt/
e) compare this with others who have been down this road already and get more accurate real world calculations of performance

Situation 2:
Given the information in above situation 1a-c, and possibly realizing that a given battery set in 1d, how do I:
a) go about finding the right battery combination necessary to run this 'system'
b) scale back the system to accommodate the said batteries above in 1d

So additionally, going back to 1d - what are some truly good resources to read about batteries. Naturally AGM is the choice, but how do I know the differences between a battery seen in the link above, vs. something like a Super Start Platinum from O'Reilly, or a Optima Red Top, both of which I believe are rated at less than 80hr. And if the batteries are nearly the same size, how is the hr rating so different?

And also, what sort of inflation value (2%?) would one use to adjust a calculated guestimate to a real world situation based on others experience in knowing real world amp values are likely higher than the rated values?

So lots of questions here. And I am more or less just overwhelmed in figuring out this system. The last thing I want to do is move on to the plan only to find out later that it was either significantly over-engineered, or won't even support said electrical loads for half of a day. I really would like to plan it right before acquiring more parts.

Thanks in advance for any input!

 

[Umbrarian]

Add up the amps they pull.

Lets say that is 10.

You have a 40 ah battery.

40 / 10 = 4 hours

 

[DiploStrat]

You may find these useful:

https://cookfb.files.wordpress.com/2016/09/plan-electrical-system.pdf

https://cookfb.files.wordpress.com/2016/09/battery-charge-slides.pdf

They come from here: https://diplostrat.org/documents/

Best wishes!

 

[dreadlocks]

those 12v heating pads are gonna kill yeh, any chance of putting the furnace in the same compartment as the water tank and using an open air intake from there to circulate air? also a diesel water heater can be hooked up to a heat exchanger with engine coolant and this will give you engine heat and negate the need for an oil pan heater, it will also let you use waste engine heat for water/heating.. you dont really need a diesel air heater if your doing a diesel water heater either, you can get both out of a single unit more efficiently.. Unless you walk away from these 3 heating pads then your never gonna fit enough solar to be useful..

Battery charge times w/lead are going to be long regardless of how many amps your alternator can put out, most of a lead battery charge is far from full amps.. absorb takes hours and its only taking a small fraction of what your charger can give it.. if you really want to dwell for 3 days your going to have to likely run the engine >8h to top it back off.. an ideal system will see the lead batteries fully recharged daily, lead based batteries dont like to sit days on end with a partial charge if you want em to last.. If you go out for 2-4+ weeks and that entire time you struggle to get it back to 100% they will likely have degraded performance afterwords, especially with AGM; at least mine have.. the previous system I did was designed too last that long between recharging, but I failed to account for the fact that I would rarely drive long enough to fully recharge it between stops and it was a loosing battle on the road.. the AGM's only survived a few of these abusive trips before giving up on life..

Consider a small genset for charging the batteries more frequently so you dont have to drive as much or idle your expensive engine all day.. solar in winter (shorter days, lower sun, snow/ice) with limited roof space and high electrical demands is going to be a very hard battle to win.. you might only be able to achieve a little more runtime before an engine is required.

 

[Joe917]

Get rid of the heating pads. Design your build to have the water tanks inside the insulated portion of the camper. The camper, the hot water tank and the engine preheat can all be handled by a well designed Webasto or Esparcher system. That will reduce your loads considerably. Add solar, (assume 4 hrs a day X panel amps).
AGM is not the natural choice, 6 volt flooded golf cart batteries will give the best price per amp/hr and last.

 

[Chorky]

those 12v heating pads are gonna kill yeh, any chance of putting the furnace in the same compartment as the water tank and using an open air intake from there to circulate air? also a diesel water heater can be hooked up to a heat exchanger with engine coolant and this will give you engine heat and negate the need for an oil pan heater, it will also let you use waste engine heat for water/heating.. you dont really need a diesel air heater if your doing a diesel water heater either, you can get both out of a single unit more efficiently.. Unless you walk away from these 3 heating pads then your never gonna fit enough solar to be useful..

Battery charge times w/lead are going to be long regardless of how many amps your alternator can put out, most of a lead battery charge is far from full amps.. absorb takes hours and its only taking a small fraction of what your charger can give it.. if you really want to dwell for 3 days your going to have to likely run the engine >8h to top it back off.. an ideal system will see the lead batteries fully recharged daily, lead based batteries dont like to sit days on end with a partial charge if you want em to last.. If you go out for 2-4+ weeks and that entire time you struggle to get it back to 100% they will likely have degraded performance afterwords, especially with AGM; at least mine have.. the previous system I did was designed too last that long between recharging, but I failed to account for the fact that I would rarely drive long enough to fully recharge it between stops and it was a loosing battle on the road.. the AGM's only survived a few of these abusive trips before giving up on life..

Consider a small genset for charging the batteries more frequently so you dont have to drive as much or idle your expensive engine all day.. solar in winter (shorter days, lower sun, snow/ice) with limited roof space and high electrical demands is going to be a very hard battle to win.. you might only be able to achieve a little more runtime before an engine is required.

Well the heating pads for the water tank is more for use when the engine is running. I would imagine only using the oil heating pad for a short amount of time when it is super cold, not on a regular basis... But I did certainly consider how much power they draw, and it's a lot... I wanted to list them more for sake of discussion as I'm not sold on the idea myself yet either. The design I'm coming up with has the water tank mounted permanently in a custom bed, so the camper portion would exclude a water system other than the physical hoses and fittings, thus keeping weight low, but also allowing me to have a water resource even when I dont' have a camper on the truck - something I always find a need and want for when working. So I suppose I could also mount a diesel air heater in the compartment with the water heater as you suggest, and have thought of that. But I'm not sure how I would then plumb that into the removable camper. I had thought about using just an entire coolant system with radiant heaters, but I'm not sure I like the idea of having all my eggs in one basket...

As for the plumbing of the engine coolant to a heat exchanger. The problem with this is I would have to run maybe 10-15' or more of hose under the truck to get to the water heater area, for each line. So that's 30' or so of extra hose. Under the vehicle. That can get ripped, torn, or punctured. Plus, that's a ton of extra coolant. (and I also don't know which way the coolant moves through the heater core). It's a good idea, and I love the idea, and was my initial thought when considering a diesel system. I'm just really concerned with having to run that much exposed hose to be honest. And the heat loss might make it not so worth it?

So this is where I get confused because I was just chatting with someone earlier who has 4 6v's to power his 'house', and after a good weekend's worth of use down to maybe 70%. They are fully recharged (or mostly) within a few hours of driving. Yet I see so many say you'll have to drive over 6 hours minimum. So I guess I really don't get where the disconnect is with these different discussions I see and what is the cause for a 5 hour difference in engine run time. I've also heard others who plug in and still never get a full charge (so maybe something wrong with the bank or the electrical connections?). In any case, this is part of the reason for this post. I see an awful lot of discrepancies and would like to understand why before proceeding.

A generator is a good idea, but not really an option. Too much weight, too much space, diesel generators are expensive, etc... I'm already pushing the envelope a lot for this truck, simply due to the equipment I carry on a normal basis. I'll probably be nearly 2k over GVW, and still have more weight from towing trailers at times. If I resorted to having to have a generator, then I would probably scrap the idea as a whole, and figure out another option honestly.. It would be great to have for so many reasons...but there's just only so much I can pack on the truck.

Get rid of the heating pads. Design your build to have the water tanks inside the insulated portion of the camper. The camper, the hot water tank and the engine preheat can all be handled by a well designed Webasto or Esparcher system. That will reduce your loads considerably. Add solar, (assume 4 hrs a day X panel amps).
AGM is not the natural choice, 6 volt flooded golf cart batteries will give the best price per amp/hr and last.

I think I addressed the heating pad/engine preheat above. Running it all in to the truck's cooling system was my initial thought, but I'm not liking the idea of such a long run of exposed coolant hoses...

The reason I am going with AGM batteries is the condition operated. I operate on much rougher roads on a much more consistent basis than most and really do not think a 6v would stand up to the abuse for very long at all. Maybe I'm wrong....but when 50% or more of my drive time is on washboard roads with bumps and dips enough to jar your noggin...I had figured AGM was the way to go (and I do go slow when warranted - no need to destroy my truck). But then again, if the options for AGM batteries available show to be insufficient, then 6v may still happen.

 

[Joe917]

Running extra coolant lines is pretty simple. Wrap them in foam pipe insulation and run them along the frame. I would look at radiant heaters, not an "air heater". Your big complication is wanting to separate the water system from the camper. If you want to continue with that idea, hydraulic line quick couplers might help.
Flooded golf cart batteries will take rough roads.
The 6 hours driving to full charge is a reference to the fact that lead acid batteries have a long absorb phase in the charging cycle. Finishing the charge cycle with engine power or a generator makes no sense, get solar.

 

[dwh]

Lead-acid batteries charge up to 80-90% full fairly quickly (called "bulk stage" in a multi-stage charger)...a few hours (4-6) of driving will usually do it. That last 10-20% (called "absorb stage" in a multi-stage charger) can easily take twice as long.

Unfortunately, sulphation happens faster any time the electrolyte of a lead-acid battery is at less than 100% fully saturated with electrons.

Cronic undercharge (rarely, if ever, getting to 100%) is the number one cause of premature end of life for lead-acid batteries.

AGM is a lead-acid battery.


What you are asking about in your original post is "energy budget". When estimating for say, a solar powered house, the way you do it is first figure out how much energy budget you need, then build a system to supply it. But for vehicles, you first figure out much you'll have, and then figure out how to stay within that budget.

So for a house you know how much power you'll need, and can size the battery bank to supply that and the solar to recharge the battery bank.

With a truck you need to know how much you can generate, then size the battery bank to store it. Or, more often, how much battery you can carry, which determines how much you can store, which sets your energy budget.


Since you already understand the basic concepts such as consumption over time and duty cycle, there is no need to go into all that. The math is fairly simple. For example, let's say a fridge that draws 5a (per hour) and generally has a 50% duty cycle.

5 x .5 gives you the hourly average
hourly average x 24 gives you the daily average
daily average x number of days

Do that for each load. Mostly it'll be a lot of WAGs (wild-assed guesses) so add in a nice fat fudge factor. Total it up. Compare to your energy budget. Get the two as close together as possible, either by beefing up the generation/storage, or by trimming the loads.


One way to quickly double the budget is deciding right off that you are going to fry your batteries. That's how I did it before I stumbled over a killer deal on 400ah of AGM battery and 300w of solar.

The way that works is simple - ignore the "50% rule". Most deep cycle lead-acid batteries have a sweet spot where if you drain them no more than 50% and then fully recharge, you can do that about 1000 times before they are at end of life. So the 50% rule has become the common wisdom for a balance between usable energy budget and battery life.

That's fine for a house, but to me, on a vehicle, that's double the ballast. Or half the energy budget. And those same life cycle charts usually show you'll get maybe 500 cycles by ignoring the 50% rule - the curve flattens out.

So I'd buy the cheapest deep cycle batteries I could get and just hammer them by ignoring the 50% rule. I'd get half the life and have to replace twice as often. But so what who cares...they cost half as much so the expense works out the same over time.

And who gives a crap about washboard? Or chronic undercharging? They aren't gonna last more than a couple years anyway.

And I had nice new batteries every couple of years.

And double the energy budget.

 

[dwh]

I should also say that once my current pair of Chinese 4-D size 200ah AGMs wear out, I'll almost certainly replace them with 4 x 6v golf cart deep cycle "traction" batteries. The only reason I have the AGMs is that my nephew bought them and the 300w solar panel as a package deal from a guy here on ExPo, and then never used them so I took the whole load off his hands.

And I fully plan to once again double my budget.

 

[J!m]

I’m going to avoid the electrical portion of the discussion, and comment on the water running to the rear (or wherever).

I have a hot water shower, so I run tank to the pump (after a filter) then to a tee under the truck. One side goes to “cold” tap and the other continues forward to a stainless plate heat exchanger under the hood. That circulates coolant on one side and the tank water on the other. These are ~95% efficient. (In other words: damn hot!)

Hot Output from the HE goes next to the “cold” water tap, where I attach my shower control.

Point is, keep the engine coolant safe under the hood and run only water under the truck. If it does get damaged somehow, it can be field repaired easily and you don’t risk the engine coolant circuit. I used food grade PE tubing which is strong and light.

 

[Joe917]

I’m going to avoid the electrical portion of the discussion, and comment on the water running to the rear (or wherever).

I have a hot water shower, so I run tank to the pump (after a filter) then to a tee under the truck. One side goes to “cold” tap and the other continues forward to a stainless plate heat exchanger under the hood. That circulates coolant on one side and the tank water on the other. These are ~95% efficient. (In other words: damn hot!)

Hot Output from the HE goes next to the “cold” water tap, where I attach my shower control.

Point is, keep the engine coolant safe under the hood and run only water under the truck. If it does get damaged somehow, it can be field repaired easily and you don’t risk the engine coolant circuit. I used food grade PE tubing which is strong and light.

How do you keep the water lines under the truck from freezing in sub zero temps?
If the OP wants to use the engine for heat he will have to run coolant lines. The coolant lines run properly will be no more exposed than the lower rad hose.

 

[dreadlocks]

Many rear engine water cooled vehicles exist, there is no technical problem with running coolant lines from the front to the back.. your fuel lines likely run the same distance without getting snagged or hung up on things.. If you have frame rails you can do hardlines pretty easy.. I assume this is a Diesel Van or RV from the descriptions, run a marine heater core in your living quarters plumbed up w/engine coolant.. Diesel water heater plumbed directly up to coolant.. transferring heat around with water/liquids is going to be far more efficient than ducting and you'll have heat out your console vents and your rear heat exchanger as well as a warmed up engine ready to start in even coldest of temps and without needing to drive long enough to get heat/defrost.. If you want hot water you can setup a small internal loop pumping through a heat exchanger w/engine coolant that is easy to drain if you need to winterize it.. but even if you drain the fresh water system you still have heat in the back when engine or diesel coolant heater is running.

 

[J!m]

I do run heater hose to my second heater, behind the passenger seat side bulkhead in the rear of my truck. I ran them on top of the frame. No way they’re getting damaged, and if they do, I’ve got bigger problems!

But I have a drain in the water tank to clear it out. I did Grenade one of my sediment filters when it got very cold one night... but the tubing is PE (pex is similar) tubing so it can freeze if neglected without bursting. If it’s a circulating (closed) system you can add alcohol etc. to lower the freezing point too.

 

[Chorky]

Well thank you all for the great information and discussion so far!! Just an FYI I do have another thread going specifically for water heater systems at:https://www.expeditionportal.com/forum/threads/water-heater-the-tank-only.202004/

FYI this is all to be going on/in a dedicated custom flatbed with boxes for a '97 F350 diesel crew cab


I wanted to try and keep discussion topics separate just to prevent confusion of myself, and for others trying to learn similar things. So back to the electrical stuff....
1) I will spend some time trying to guestimate hr's needed. It might take a few weeks though we'll see. I think this is the first bit of information that will truly be needed to go any further in terms of batteries needed.
2) I like the comment about the energy budget. I think ultimately there will be some potentially significant compromises needed for my ideas in this in terms of making the system capable of handling the 'absolute necessity' of systems, at the cost of maybe only handling the 'extra's' at times when either plugged into shore power, or while the engine is running, or for say one day rather than 3 without charging.

More questions:
1) in the mean time, I many times see the word 'golf cart' batteries being thrown out there. For the good of the group (and myself) can anyone expand on this? In other words, what specifically is a golf cart battery. Is it just any standard 6v that can be found from various manufacturers? Or is it a specific part number, etc...
2) if one did not want to use a 6v still, what recommendations would you all have for normal 12v AGM batteries? Specific brands?
3) let's talk batteries....I've looked up info before about different groups but found information that was not very detailed. Where can I find very specific detailed information that actually explains why different battery groups have different specs. Is it only size that is different which allows for bigger plate surface area or are there other differences?
4) from those who have solar, do they really provide enough of a charge to make it worth it?
5) one question that also relates to this topic, but is different, is wire sizing. Any recommendations on how to go about assuming the correct wire size needed. Let's use a different topic as an example. Let's say, for my specific truck with two factory batteries, hooking up a winch. So a 16.5 warn can pull up to 610 amps, but the winch might be connected to the primary battery. Naturally this could cause a potential 300a draw from the secondary battery which may only have a, say, an upgraded 2/0 battery to battery cable. Now how would one calculate necessary cable size for this particular draw. To put it in another more relevant situation. Let's say I decided on 2, (or maybe 4) 12v AGM batteries in the bed as the 'house' batteries. Lets estimate the wire run needed to be, say, 12'. Now lets say my upgraded MeanGreen alternator puts out a max 200a. How would one go about calculating the wire size needed for this run? I ask because several sources I have looked at online have different values, thus causing confusion compared to my own electrical knowledge...
6) another relevant situation was to utilize a manually switching 200a solenoid to separate the house batteries from the vehicle batteries. Now, in having 2 separate electrical 'systems', what do some of you use to decide what component gets hooked up to what system? So for example, taken to consideration all the components above, that would be mounted in the bed, the 'cleanest' way would be to have all those components wired to the 'house' batteries. But, would this be the better way, in your opinion? Or should some things like the compressor be wired to the engine batteries even though it is mounted to the bed.
7) to caviat off of #6, lets talk charging. The plan is to also include a shore power charger, for when I'm at camp sites, or in the future when I have a house, if that ever happens (I live out of this truck, but in a travel trailer, which hopefully soon will be replaced with the camper this system is being designed for). So, what are some preferred methods of charging? Would a dedicated in bed mounted 'car charger' be better? I do not know what shore power charging options are available. Of course it would be nice to have something that can utilize a standard 30a RV circuit as those are easier to bring down to a normal wall outlet, but do take advantage of a higher amp circuit if one is available. 50a circuits are still not as readily available for the places I have seen as a 30a is.

So I'd buy the cheapest deep cycle batteries I could get and just hammer them by ignoring the 50% rule. I'd get half the life and have to replace twice as often. But so what who cares...they cost half as much so the expense works out the same over time.

And who gives a crap about washboard? Or chronic undercharging? They aren't gonna last more than a couple years anyway.

And I had nice new batteries every couple of years.

And double the energy budget.

This is a most excellent point!! Thinking about it it is simple economics and something to be considered along with everything else to avoid a super complex system. After all, simplicity is the goal - for me anyway. Well, that is making the system as simple as possible while achieving a overall goal.

I’m going to avoid the electrical portion of the discussion, and comment on the water running to the rear (or wherever).

I have a hot water shower, so I run tank to the pump (after a filter) then to a tee under the truck. One side goes to “cold” tap and the other continues forward to a stainless plate heat exchanger under the hood. That circulates coolant on one side and the tank water on the other. These are ~95% efficient. (In other words: damn hot!)

Hot Output from the HE goes next to the “cold” water tap, where I attach my shower control.

Point is, keep the engine coolant safe under the hood and run only water under the truck. If it does get damaged somehow, it can be field repaired easily and you don’t risk the engine coolant circuit. I used food grade PE tubing which is strong and light.

I do like this thought quite a lot as it avoids an extended coolant hose run under the vehicle to the bed, but like Joe asked above, how do you keep your water lines from freezing? For one I am moving to a very cold climate where people's water mains that are buried 8' below the ground freeze at times. Also, how would you get the bulky heat exchanger under the hood? I imagine even a plate is bulky, and as someone else mentioned, probably not as efficient as an actual 'hot water tank' especially for super cold climates?

 

[DiploStrat]

You really need to do a bit of reading on your own, rather than simply shotgunning questions to the Internet. You are going to have some serious $$$ tied up in this.

This may help: https://cookfb.files.wordpress.com/2016/09/battery-charge-slides.pdf

To one of your specific questions, you want a deep cycle battery, not a starting battery, for camper use. In simplest terms, a deep cycle battery has fewer, larger plates. While it won't give as much of a starting surge, it will give a steady output longer and is more resistant to damage from deep discharge. These are the batteries sold for use in things like golf carts, forklifts, etc. They are also sometimes called "Traction" batteries.

I discuss wire size in my slides.

Hope this helps.