Need a little help designing lifepo4 system with alternator charging

baltik

New member
Fair point about the starting battery, still would love to be able to taper my output to 35-40 amps to keep the heat down. I am running a Subaru ej22 in my vanagon with a 70a alternator so not a lot of power to spare and definitely no thermal control
 

john61ct

Adventurer
DC-DC charger sized for the max limit you want.

BSS CL- style 7600 VSR now discontinued, is set around 60A, can pick up on eBay sometimes.
 

CoyoteThistle

Adventurer
I'm running a 100amp LiFePO4 in our pop-up camper (CALB cells and DIY control system). My two cents:

1) Go with the DC-DC charger unless it is really cost-prohibitive for you. Simple and they seem to work. When I was building my control system there was very little info on how the DC-DC chargers were working with lithium and few (if any??) were really set up for lithium charge profiles (this was about three years ago). The system I designed and built is detailed in my build thread starting here with more details later in the thread if you're interested. It's effective (as are other solutions discussed around here and elsewhere) but comparatively complicated. Also, my truck's alternator has thermal protection (I see 80 amps for a brief time after start-up that then drops to about 35 amps constant); if you don't have thermal protection the DC-DC is an even bigger no-brainer. Think about where you want to be on current limiting though, a constant 30 amps from a 70 amp alternator may be high. Seems like about 25% capacity is where most automotive alternators like to run long-term.

2) Go with the 180-200 amp cells if cost and space allow. We have similar power demands to you I think: an Isotherm DC fridge, LED lights and a Propex heater as the main loads (and a canvas pop-top up at night letting the heat out ;)). We recently got two days and two nights out of a full charge with no solar (in the shade) with warmish days and cold nights (heater working pretty hard). 80 amps consumed total. Of course, YMMV.

Good luck with it!
 

mrfoamy

Mrfoamy
Need a LOT of help designing lifepo4 system with alternator charging

Soon I am taking delivery of a 2019 F350 with 377 amps output (twin alternators, twin batteries). I plan to connect a starter battery (with a PAC 500-amp isolator) to two 100 amp/hour Battleborn house batteries in my slide-in TC using a 1/0 cable, and no B2B charger (since Battleborn says it may not be needed)…then check for overheating anywhere along this connection.

This might flow ~100 amps (fused 200) and charge two completely discharged LiPos in 3 hours. I assume the 7-wire harness that connects the truck to the camper (#10 wire) might also flow ~25 amps so charging flat batteries might be well under 3 hours. If anything gets too hot, I’ll install the B2B which will choke amperage to 60 amps and take longer.

Questions:
  1. Should I connect: only one starter battery to the isolator or one alternator to the isolator (as shown in PAC’s instructions)?…or both batteries, or both alternators? Continuous service of that load seems like a lot.
  2. Do I need to fuse the negative cable? I can’t see why. Both cables will run to an Anderson connector in the bed.
  3. Ideally an Upfitter switch will control the isolator but PAC does not specify a wire size or amp requirement. How small can this wire be and size fuse?
See if I’m thinking correctly:
I’m not bothering with solar or a generator since Ford is providing me with a free, convenient, fairly quiet, diesel 3,800 net-usable-watt generator with a 36 gallon fuel supply. Utilizing the high-idle option Ford provides (SEIC), just flip a switch (or dial a potentiometer) to raise the idle. Should be easy to wire the SEIC to an upfitter switch (with a potentiometer set to idle at the alternator sweet spot). Just not overly long with the diesel at high idle.

I expect there’s enough power for air conditioning and an induction range simultaneously, and still have juice left over to charge house batteries (assuming a big inverter and associated wiring)…Ok…don’t have those…Just saying.
 

Verkstad

Raggarkung
Ideally an Upfitter switch will control the isolator but PAC does not specify a wire size or amp requirement. How small can this wire be and size fuse?
If you read the ’specs from PAC, you would find that relay draws ”less than one amp” I assume thats at 12V, (their documentation is shitty)... 10-15W is typical to those type of relay coils regardless.
Btw, I think that relay is made by White-Rodgers, badged for that PAC company what seem to cater to the idiots and con artists of audio business. Its no wonder PAC documentation is shitty.
 
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DiploStrat

Expedition Leader
The 90A version of that beast looks interesting. Most Big Three pickups should be able to sustain 100A indefinitely. But how does it limit the current? The massive heat sinks might provide a clue. I would be curious.

It also claims to prevent back flow. Diodes? It looks like this may be effectively a key controlled or fully single side sensing intelligent relay.

The spec sheet calls for an additional Mastervolt component with LifFePO4. Is that only for Mastervolt batteries? How would this thing work with home-brew or off the shelf LiFePO4?
 

cabnetguy

New member
I was planning to run wire directly from the relay into the second input on the solar control!er. The controller that I will be using will perform all the cell balancing,voltage etc. It sounds to easy doesn't it? If you see any problems with this plan let me know.

Brian
 

DiploStrat

Expedition Leader
I was planning to run wire directly from the relay into the second input on the solar control!er. The controller that I will be using will perform all the cell balancing,voltage etc. It sounds to easy doesn't it? If you see any problems with this plan let me know.

Brian
Quick look at the manual of the Electrodacus indicates that this would be a terrible idea and should fry it in short order. I have never heard of anyone connecting the regulated output of their alternator into a solar controller. (Doesn't mean that it can't be done, but I have never heard of it. Nor do I see any reason to do it.)

I defer to the opinions of others.

Good luck!
 

cabnetguy

New member
I am using the SBMS120 that has a capacity of 75amps for each input. I was planning to use the 40 amp version of the relay, so this shouldn't overload anything? I am a woodworker not an electrician so not trying to argue, trying to learn.
 

luthj

Engineer In Residence
Only a handful of solar controllers will work properly with a lower voltage input from the alternator. Ctek and maybe some Redarc models? Most MPPT controllers require the input to be at least 3V above the desired charging voltage. Some PWM controller would work, but they must have a higher frequency to avoid odd alternator regulator loading I would think. In theory a PWM solar charge controller could be used to limit alternator charging current. It may have some unintended consequences though.

A relay is just a switch with a electrical control coil. Some items labeled relays are more complex that that. A solid state relay may be capable of performing PWM style current regulation, but I have not seen any.
 

cabnetguy

New member
I thought this sounded to easy. So the best way to do this would be the sterling dc to dc charger. I would have to go look at website, but doesn't this replace the built in regulator in the alternator to get the higher voltage?
 

luthj

Engineer In Residence
The sterling B2B chargers do not modify the alternator. They just convert the voltage to whatever you set it to.
 
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