4 Questions: 377 amp alternator charging LiPo system

[luthj]

I've come across this a few times, and to me translates to reinforcing "don't use drop-ins".

Can you point to first-hand threads where this is credibly documented?

Or does BB actually admit to that limitation?

Finally, advising using wiring gauge to limit current is generally dangerous. That's what fuses are for.

Some reading here at post 6. I can't find the detailed posting by HarryN, but essentially he was using 2 BBs and despite being inside the published limits, the internal BMS fried. He was running a small AC unit I believe, but I could be mistaken.
https://sprinter-source.com/forum/showthread.php?t=68518

Some more discussion scattered on this thread by calbiker and myself (midwestdrifter). BB uses a disconnect temp of 135F, and their internal solid state relay has a resistance of around 17 mOhm. That is quite a bit of dissipated power in the relay at high currents.
https://sprinter-source.com/forum/showthread.php?p=712234

With regards to charging, sizing your cables to drop around 1-1.5V can safely and economically limit charge current to lithium batteries.

 

[dwh]

The single sensing only comes in to play when the relay is open, and the two sides can be at different voltages, and you can trigger to close the relay when one voltage exceeds a threshold. Once the relay closes, the voltages on both sides of the relay are the same, right? So at that point it doesn't matter which side it is sensing, it will stay connected until the voltage of both batteries goes below the disconnect threshold.

Correct.

Edit: And the disconnect threshold on the Blue Sea kit (ACR or ATD) is set for lead-acid and is too low for Battle Borns.

 

[luthj]

Depending on alternator voltage, a simple ignition triggered relay would likely work fine.

 

[dwh]

Blue Sea makes ultra high quality stuff that does what it says it does. I'd trust their engineers rather than random assumptions. Regardless, a quick call or email to them will tell the original poster for sure. In all situations, I'd rather use something from them than something from some new-on-the-block overlanding electronics company if it will do the job.

Crap.

A) We know exactly how the Blue Sea works. It's not rocket science or mysterious. You might need to call their tech support to have it explained to you...I sure as hell don't.

B) PAC is not some "new-on-the-block overlanding electronics company". They sell stuff for high power audio. Not that it matters, the OP is looking at a basic dumb solenoid from PAC to be rigged as a simple "split-charge relay". Any old solenoid will do for that as long as it has a continuous duty rating. He probably decided on the PAC solenoid due to the 500a rating.

 

[john61ct]

With regards to charging, sizing your cables to drop around 1-1.5V can safely and economically limit charge current to lithium batteries.

OK, so say I had a nominal 48V 700Ah LFP bank, and my 55V charge source can only put out a continuous 40A safely.

Wire routing distance is 20', so total say 45' round trip. Using UL1426 105c tinned boat cabling, what gauge wiring would you recommend?

And ideally, please point me to resources to help me learn how to do the calc myself for other use cases.

And I guess that would require a separate discharge buss, since peak current needs to hit 200+A.

 

[dwh]

That is an interesting thought, but may have issues as the panel voltage can go up to 22V, and ideally it would also sense the alternator side as well. Really what we need is an ACR with programmable set points, preferably individually adjustable for each side and an ignition trigger. There are some products that are close, but nothing that is quite right.

Exactly. Prolly have to "roll your own". Something like a dumb relay controlled by an adjustable voltage board.

https://www.amazon.com/WINGONEER-di...C_SX236_SY340_QL65&keywords=voltage+relay+12v

Which is nothing new. Someone around here already does that with his lithium setup. jonyjoe maybe?

 

[Rando]

OK, so say I had a nominal 48V 700Ah LFP bank, and my 55V charge source can only put out a continuous 40A safely.

Wire routing distance is 20', so total say 45' round trip. Using UL1426 105c tinned boat cabling, what gauge wiring would you recommend?

And ideally, please point me to resources to help me learn how to do the calc myself for other use cases.

And I guess that would require a separate discharge buss, since peak current needs to hit 200+A.

I am sure you can do this calculation yourself - here is the cheat sheet: V= IR, and here is some data to show the effect of various LiFePO4 charge voltages:
https://www.powerstream.com/lithium-phosphate-charge-voltage.htm

 

[dwh]

If the Battle Borns really do have issues at charge rates above C*.5, then also considering that the new Ford truck might have some interesting programming as regards the voltages/temps/engine loads/etc...

A B2B with a lithium charge profile is probably the best way to go.

 

[luthj]

OK, so say I had a nominal 48V 700Ah LFP bank, and my 55V charge source can only put out a continuous 40A safely.

Wire routing distance is 20', so total say 45' round trip. Using UL1426 105c tinned boat cabling, what gauge wiring would you recommend?

And ideally, please point me to resources to help me learn how to do the calc myself for other use cases.

And I guess that would require a separate discharge buss, since peak current needs to hit 200+A.

I need to dig up some resources, it may be a while. The key to doing this effectively is either testing the bank with a variable voltage charger, or getting the MFG to supply curves showing charging votlage and battery acceptance current.

To size the wire, find the charge voltage that corresponds to the max current you desire. Assume 50A which yields 13.4V or similar (just a guess). Subtract 13.4v from the alternators voltage when loaded. Say 14.4V-13.4V=1V for example. V=I*R 1V=50*R R=20mOhm. For a 15ft run, that yields 1.3mohm per foot, or about 1AWG (note that the fuse and terminal resistance may need to be calculated in). Obviously I just pulled these numbers out of the air, so they will vary for each cell type. There is going to be a limit to how much power the wiring can dissipate (ampacity), but assuming you have at least 10ft of cabling, this is not likely to be an issue.

Not all MFGs will provide this data, so a few brief experiments can help dial in the desired Vdrop for the wiring to limit charge current. I have used a similar approach in large lead banks. Lithium is a bit easier, as its charge curve is extremely flat outside the knee area.

Another method with an already installed system, is to use one or more extra fuses. The fuses have a known resistance, so they can effectively be used to tune the charge runs resistance for ideal charge current.

 

[mrfoamy]

But I'd bet a pair of BBs could absorb more than 100a. Running the 1/0 from both alternators to the relay would be optimal.

Depending on alternator voltage, a simple ignition triggered relay would likely work fine.

A B2B with a lithium charge profile is probably the best way to go.

Another method with an already installed system, is to use one or more extra fuses. The fuses have a known resistance, so they can effectively be used to tune the charge runs resistance for ideal charge current.

Before I call Blue Sea or BB, see if there is common agreement with the quotes above. I may use some or most of these recommendations.
But Post 23, I need a specific referral for a “A B2B with a lithium charge profile”. Thanks for all the advice.

 

[luthj]

Most lithium-iron-phosphate packs will happily charge from anything above 13.6v with varying rates of course. The only reason I see a B2B charger being necessary is as a way to limit charge current. As mentioned above a dumb ignition triggered relay and modestly sized wire/cable could be all you need.

You should start by seeing what your alternator voltage is, and if it varies significantly during driving. A 12v outlet voltmeter is an easy way to monitor it. If the voltage is not in a range acceptable for charging your batteries, then you would go with a B2B. Otherwise a simple charging relay would be my suggestion.

 

[DiploStrat]

Before I call Blue Sea or BB, see if there is common agreement with the quotes above. I may use some or most of these recommendations.
But Post 23, I need a specific referral for a “A B2B with a lithium charge profile”. Thanks for all the advice.

You REALLY need to do some homework - your expectations of what you are going to get out of batteries is a bit exaggerated. Trying to run an air conditioner and an induction cooktop at the same time is going to fry something.

That said:

-- Battle Born will tell you the maximum charge amperage for their batteries. They may run it a bit high, but the general experience is that LiFePO4 batteries are a bit like black holes for amps. Where lead acid tend to resist a charge, with LiFePO4 the threat may be to your alternators - they may overheat because of the high draw.

-- The problem with the Blue Sea ACR (and most others) is that they open at 12.7v and close at around 13v. Many LiFePO4 batteries rest at well over 13v, so the relay will never open. (See previous comments by folks who already have this type of system.) Viltron does make a voltage sensing relay that they market for just this purpose. It has different voltage settings from the Blue Sea but it is also intended to be integrated with an all Viltron system. The advantage of a key controlled relay is just that, it is controlled by the ignition key. Blue Sea does not sell an adjustable ACR but they will sell you a nice 200A relay.

-- Almost any modern B2B will have a LiFePO4 setting and Sterling, at least, offer pretty complete customization. While B2B were originally developed to boost voltage, with LiFePO4, the advantages are: voltage cut and current limiting to protect the alternator.

So the real question is whether the charge profile of your truck is acceptable to Battle Born batteries and whether 200+Ah of LiFePO4 will fry the alternators. If not, a key controlled relay should be great. Else, a B2B is probably much safer.

And, you need solar. Maybe a bit less with LiFePO4 than with lead acid, but amps is amps and you need lots of them.

EDITED TO ADD: See Jon's post above. He's making sense.

 

[dwh]

If he's got 377a of alternator then I doubt he'll hurt the alternator with two Battle Borns. Battle Born has already told us that their BMS will disconnect if the current exceeds 100a for 30 seconds (reconnect in 5s) or 200a for .5s (again, reconnect in .5s).

But if their BMS really does have heat-related issues (failures) at >50a sustained, then I'd be more worried about limiting the current.

Plus, they don't need to be held at a higher voltage once charged, so if the truck's computer holds a steady higher voltage, that might not be so great. Or, if it cranks up the voltage based on temp...I seem to recall one guy who couldn't use Sterling because his truck's computerized system went above 15v on occasion.


So...IF the Battle Born BMS actually does have issues at >C*.5, OR the truck voltage is excessive for sustained periods, THEN the split-charge relay might not be the way to go.

In which case, B2B.

 

[dwh]

https://www.expeditionportal.com/fo...-d250s-b2b-charger.173120/page-2#post-2317523

 

[DiploStrat]

...
Plus, they don't need to be held at a higher voltage once charged, so if the truck's computer holds a steady higher voltage, that might not be so great. Or, if it cranks up the voltage based on temp...I seem to recall one guy who couldn't use Sterling because his truck's computerized system went above 15v on occasion.
...

SNARK! I believe that Sterling have fixed that little problem!

But it was a great learning experience. Pricy, but great.