Trying to understand DC/DC chargers

[Bear in NM]

Ok Diplostrat, you are freaking me out. Not about the amps. I stopped working a little early today, to get my electrical box out of the shed. I had my phone on my hip, just in case. I was rooting around in my box, and my phone notified me of your reply. I had a hank of 1/0 welding cable in my hand, right when you posted. You need to cut that crap out......

I am going to run a length of #4 from my dual batteries to a Warn/Anderson type connector to just behind the batteries tomorrow. Then I will make a pigtail with the connector mate, to run into the back of my van. Total run will be less than 6'. I'll probably throw a manual disconnect inside. When doing engine wiring, I like to use the blade style fuse, screwed to the battery post. This makes for one less connection. On my van, it takes a floor jack to lower both batteries from the frame rail, but I am still gonna do the blade fuse. I may regret that, but I have yet to blow one of those, and I haven't burned a vehicle the ground.....

I hear you loud and clear about the amps, time and heat. If I do a LiFePO4, the max would be 80-100 ah. And the way I travel and camp, I plug my fridge into the starting circuit of my vehicle when driving, and switch to my house battery once I arrive. To date, I've not really needed to charge and drive. But I am wiring just in case, to handle a reasonable draw.

Appreciate the warnings, but the mind reading not so much.......:bowdown:

Craig

 

[DiploStrat]

Got to get on the road. In the interim, a friend of mine is building a camper with a 1240D and Stark Power LiFePO4 batteries: http://forum.expeditionportal.com/threads/184366-DIY-Composite-Flatbed-Camper-Build

You will also see posts by Coyote Thistle, who has do some good looking work with a home brew LiFePO4. See: http://forum.expeditionportal.com/threads/168085-Pro-Rig-V2-0-Home-Built-Compact-Composite-Pop-up

These folk should give you some real world data.

 

[dwh]

I am very concerned about my Arb 63 and whether the lowest voltage cut-off setting is going to limit me with a LiFePO4 battery. I am a lot weak on LiFePO4 SOC's, and am not sure whether I would be able to get the full 80% discharge.

No worries. Take the Victrons for example:

https://www.victronenergy.com/uploa...-Volt-lithium-iron-phosphate-batteries-EN.pdf

4 cells. Full charge voltage 3.2v/cell, full drained voltage 2.5v/cell. So 100% drained is 10v, but to protect the cells from undervoltage damage (ya, that's a thing), The internal BMS cuts the output at 11v.

But by that time, you're past 90% drained. Most of the "12v nominal" LiFes are around 90% drained by the time they get to 12v or so.

As long as your fridge LVD is set lower than 12v, you'll get more than 80%.

 

[Bear in NM]

DWH,

Thanks for the info. I took a look at the link. I have figured out after reading a lot more, including Diplostrats links that I need to be opened minded about the actual brand. My local solar place carries one brand, and they told me that they have not sold very many. He could not give me local feed back. But more importantly, it is very clear that any maker needs to have detailed info available, like your Victron link. The BMS appears to very critical.

The other hanger that I have been contemplating is the issue of charging below freezing. Being in the Rocky Mountains, fall and certainly huntings trip in later fall could be problematic. It appears that cold weather does not affect storage nor discharge, but it gets cold around here. I do not need to thrash on my batteries, but I am not looking to be stressing over batteries.

I decided to run the 1/0 cable into the back of my van, rather than the 4. Got it done this weekend, along with gutting a bit of PO goofy wiring. So the van is at least solar capable, with my solar suitcase.

Craig

 

[dwh]

https://wolverineheater.com/collect...el-filter-heater-12-volts?variant=35118711954

https://www.comstatinc.com/thermostats/snap-disk

 

[Bear in NM]

Well, the heater looks darn interesting. I put one in my amazon wish list, for later. That looks handy, and given that my new van is diesel, might not be a bad idea to have one of those in the kit.

I need a less tired brain to wrap noggin around the thermostat.

Thanks for the help,

Craig

 

[DiploStrat]

If you are considering LiFePO4 batteries at any time, simply place them within the heated camper. (My batteries, AGM, are under the dinette seat.) This will keep them warm. You can also route the water lines of a hydronic heater, like Jim Rixen's unit [http://rixens.com/products-services/sprinter-class-b-and-c-rv/] around the batteries to keep them warm. See the Advanced RV video that shows how they keep their water tanks warm - drill down on the Rixens site.)

 

[teotwaki]

They also isolate much like worthless diode type isolators.
That is, current thru a DC-DC apparatus is a one-way operation. For example, if you ever added solar to charge your house battery, solar wont be able to charge chassis battery.

Not true with the CTEK250S Dual. The device's solar charging puts the house battery as a priority but will switch to charging the chassis battery afterwards.

EDIT: wanted to add that you can purchase solar charge controllers that can handle two separate batteries from one solar panel bank

MorningStar SunSaver Duo 25 Amp 12 Volt PWM Charge Controller


Manufacturer Part Number: SSD-25
Morningstar’s SunSaver Duo (SSD-25) is an advanced PWM two battery controller for RV’s, caravans, boats and cottages. This product will charge two separate and isolated batteries at the same time, such as a “house” and an engine battery, based on user selectable priorities.

 

[Bear in NM]

If you are considering LiFePO4 batteries at any time, simply place them within the heated camper. (My batteries, AGM, are under the dinette seat.) This will keep them warm. You can also route the water lines of a hydronic heater, like Jim Rixen's unit [http://rixens.com/products-services/sprinter-class-b-and-c-rv/] around the batteries to keep them warm. See the Advanced RV video that shows how they keep their water tanks warm - drill down on the Rixens site.)

Diplostrat, thanks for the links. I am seriously thinking that the LiFEpo is not a good technology for me. For my camping and long weekends, the spring and fall here in the rockies means that many nights are well below zero, and I have not nor intend to run heat at night. I have sleeping bags for that. My situation is quite a bit different than you folks who are living in your rigs, and need to be comfortable most of the time. There are times when I am out that the outside temps never get above freezing, and I leave my "camp" well before sunrise. And I am clear that these type of batteries can discharge and "live" below 40 degrees, but charging is the hang-up. I actually found a couple of Victron retailers in southern Colorado, which is not that far from me. But after looking at their direct battery bms and what looks like additional monitoring equipment that may be needed, it's looking like a bit much. Not from the money side, just complexity.

Verkstad and Teotwaki, I picked up a Samlex ACR-160 (per another member's recommendation), and it is a "diode" type relay/isolator. It is not a DC-DC charger per the OP, but according to the spec's, it is indeed 2-way. I have not installed it yet, as I am still designing, so no real world use. And the second charge controller in my solar suitcase is the Sunsaver Duo, and it will charge 2 batteries. It is limited to either a 50-50 or 90-10 percent charge split, but might be useful for folks who want the bulk going to house, with essentially a trickle on the starter battieries. It works very well, as advertised. The plan is install my Duo permanent in the van, install the ACR and test. Still pondering the switching design, so that I can auto connect via the ACR or over ride and isolate for the Duo. I think for me, the true DC-DC with the boost capability would only be needed with LiFepo, which I am not sure just yet.

Craig

 

[dwh]

I picked up a Samlex ACR-160 (per another member's recommendation), and it is a "diode" type relay/isolator.

Um, nope. A diode type is like the cheapo you see on the shelf at Autozone with the big heatsink.

The ACR-160 is a smart solenoid type. With dual-sensing. And the option to add a switch for force on/force off.

And the second charge controller in my solar suitcase is the Sunsaver Duo, and it will charge 2 batteries. It is limited to either a 50-50 or 90-10 percent charge split, but might be useful for folks who want the bulk going to house, with essentially a trickle on the starter battieries. It works very well, as advertised. The plan is install my Duo permanent in the van, install the ACR and test.

What will happen is that once the Duo raises the voltage of either side high enough, the ACR will tie the batteries and 100% of the Duo's output will get sent to the combined engine/aux battery bank.

It's not a problem, but sort of makes the percentage split function of the Duo somewhat superfluous.

Still pondering the switching design, so that I can auto connect via the ACR or over ride and isolate for the Duo.

It's easy. The ACR has three spade connectors. One is for a LED. The other two are for force on and force off. You just connect one or the other to ground to activate that function.

Use a double-throw single-pole center-off switch. Connect the top and bottom to the ACR spade connectors and the center to ground.

 

[DiploStrat]

Um, nope. A diode type is like the cheapo you see on the shelf at Autozone with the big heatsink.

The ACR-160 is a smart solenoid type. With dual-sensing. And the option to add a switch for force on/force off.




What will happen is that once the Duo raises the voltage of either side high enough, the ACR will tie the batteries and 100% of the Duo's output will get sent to the combined engine/aux battery bank.

It's not a problem, but sort of makes the percentage split function of the Duo somewhat superfluous.




It's easy. The ACR has three spade connectors. One is for a LED. The other two are for force on and force off. You just connect one or the other to ground to activate that function.

Use a double-throw single-pole center-off switch. Connect the top and bottom to the ACR spade connectors and the center to ground.

dwh has fast fingers tonight! Correct on all counts. The ACR-160 is perfect as long as your vehicle has the correct charging voltages - no need to futz around split charge feature of the Duo - just connect it to your camper battery and let the ACR-160 do its thing.

As far as cold goes, despite being total tropic rats, we seem to spend weeks camping where the temperature never gets above freezing. I like a good sleeping bag too, but I also want a warm shower!

 

[Bear in NM]

DiploStrat,

The charging system in my van is new to me. I do not need the alternator to charge my house bats per se, but at least carry the load of my fridge as I head to camping locations. I could plug the fridge into my start system for traveling, then switch to house upon arrival, but that would be a bit of a headache. This is why I am not thinking I need DC-DC, just yet. If I want a warm shower, I have to break out the Zodi...

Mr. Fast Finger dwh, I think you cleared up some head scratching on my ACR. If you would be willing to set me straight...I was not clear that I had to ground the minus (middle) spade. I was going to wire like my truck dual battery, with positive to positive, and negative to negative via battery connections. The start batteries are grounded to the frame/body, therefore the house bats are also grounded to the "negative bus bar". See, I pay attention to your posts ;^)

I'm a little confused about the switch you noted. Without a switch, the minus spade must be grounded (I think this is a duh moment for me), for the ACR to operate normally (automatic).

Per the Instructions (which I am sure you know):
Status spade:
1) Contact to "+" , relay is closed (start assistance)
2) No connection on Status, normal operation
3) Contact to "-", relay remains open

With the dtsp switch you described, center terminal to ground, the center switch position "off" would be breaking the negative connection and disconnecting the ACR (complete off?). The ACR wiring diagram shows the "status" spade with two lines, one to a switch to ground. A second line going to positive starter contact. I assume these two lines in the diagram are a either/or, not both, as both might make for excitement when hooking up? If I plug the lower switch terminal to "minus" ACR spade, the upper switch terminal to "status" acr spade, then the switch moved down would make the "-" connection, opening the relay. Forced off, makes sense. I am not seeing how when the switch is moved into the upper position the relay would be force closed? I am sure I am missing something obvious.

AS to the Duo, yes, with the ACR it would make no sense. That is why I was thinking of being able to disable the ACR, so I could do the 90/10, to trickle the start batteries, and apply the most to the house side, when solar charging.

Thanks,

Craig

 

[dwh]

Oh yea. Been a few years since I looked at that. Forgot exactly how they have it setup. But I was close.

You wire the status connection to the center of the switch, then one end of the switch to 12v+ and the other end to 12v-. Switch up, force on. Switch center, auto. Switch down, force off.

Which way you force it, on or off, just depends on whether status is connected to + or -.

They are showing the force on (status to +) as being powered by the ignition switch start position, but that isn't needed unless you want start assistance every time you start.

 

[DiploStrat]

="Bear in NM, post: 2453578, member: 31880".

AS to the Duo, yes, with the ACR it would make no sense. That is why I was thinking of being able to disable the ACR, so I could do the 90/10, to trickle the start batteries, and apply the most to the house side, when solar charging.

You are WAY overthinking all of this.

-- Use the ACR, with a manual bypass if you wish. (You will probably never need the bypass.) The 0 AWG cable that you are planning is perfect.

-- Connect the refrigerator to the camper battery of your choice. Try to get at least 75Ah usable. (With AGM or FLA that works out to something on the order of 100 - 150Ah, depending on how long a battery life you want.)

-- Connect the solar controller to the camper battery. The ACR will share with the starter battery anytime the camper batteries are on charge. Don't try to outsmart it with the Duo.

Done. Have a beer (from the fridge), stop worrying.

Despite all of the technobabble, battery charging is not complex - all you need is a power source at a higher voltage. There are lots of factors that influence the speed of charge, difference in voltage, amps available, wire size, etc., but these are simply technical details.

Try what I outlined above. If it DOESN'T work, then get back to us.

Now I have to see what a Zodi is ...

 

[Bear in NM]

That makes more sense. Yes, the forced start option comes with a strong warning about all the amps through the relay, and frying it. I had no intention on wiring for a jump while starting, but being able to manually close the switch will be nice to have as an option. I had not snapped to the status spade and instructions in working with a simple rocker switch. That is indeed a simple solution.

Thank you, and thanks for the tip on the samlex chargers way back when. I hard wired the one I purchased initially into my cargo trailer last year. Just picked up another that now has it's own bag as a kit to take with me or use at home on my various banks. When hooked up with a digital amp/volt read-out, I can see and confirm exactly how the stages are tripping.

Craig