? - Voltage Regulation when Charging an LFP Battery

[john61ct]

The 1:1 ratio is optional.

But all panels per SC should match, so 1 SC per panel **type** is the minimum.

Central coordination will buy little if anything in total Ah per day harvesting.

A 160Ah bank fed by a small alt does not threaten the bank long as voltage is capped, but can easily fry the alt.

Manually regulating works fine if only used occasionally, as long as not a dangerous distraction driving.

 

[shade]

A 160Ah bank fed by a small alt does not threaten the bank long as voltage is capped, but can easily fry the alt.

Manually regulating works fine if only used occasionally, as long as not a dangerous distraction driving.

Not to worry.
I'm running 18AWG lamp cord to the battery isolator to keep the amp draw down on the alternator.

Fused, of course. Safety first. ?

Actually, I started populating fuse & switch gear in the schematic, and will be figuring out wiring requirements.
No lamp cord involved.

 

[john61ct]

Yes I know EE types I might trust to specify that method of current limiting in strictly controlled conditions.

But not something I would do myself "in production" for a case with so many variables.

It's just so easy to buy the DCDC charger kit designed for this exact use case. If cost really is the issue, do the redneck workarounds as a temporary testing setup, and just cut down on meals prepared by others for a month or two, will quickly pay for it.

 

[shade]

Yes I know EE types I might trust to specify that method of current limiting in strictly controlled conditions.

But not something I would do myself "in production" for a case with so many variables.

It's just so easy to buy the DCDC charger kit designed for this exact use case. If cost really is the issue, do the redneck workarounds as a temporary testing setup, and just cut down on meals prepared by others for a month or two, will quickly pay for it.

I didn't realize I was going low rent with my plan.

I thought I was clear about:

1. Testing the system without an additional form of alternator regulation
2. Evaluating the results
3. Seeing what DC-DC charging options Victron announces in two months before committing to a further course of action

I don't mind spending money, but I'd rather not buy gear only to wish I'd waited a few months to buy something more desirable for my use.

Beyond the Sterling offerings, what specific DC-DC chargers do you recommend?

 

[luthj]

I don't see any negatives to doing some testing first. Worst case you need to splice a charging cable to add another device. Feel encouraged to log some data and post it up for us.

 

[shade]

That's what I have in mind. I'm not heading for the North Pole this year, so I have time to figure this out. John has a point about the value of regulating the alternator's output better, but I don't think it's reckless to proceed as I described.

I even have a piece of OSB set aside for a temporary backing board.

 

[luthj]

Heck, if you are careful, a pair of jumper cables and a shunt are all you need to test the battery charge rate. Not that I suggest it, but I may have done it previously...

 

[john61ct]

Sterling's the only one afaik with the user-custom setpoints.

I don't jump on new gear, let others be pioneers, at least a few years.

 

[luthj]

Some interesting testing. Not enough data in my opinion, but a nice test bed.

The issue is that they are running that alternator very slowly, even at idle most alternators are seeing 1800+rpm due to pulley sizes. Not very reaslistic in my opinion.

They were seeing 87A on a 300A lithium battery at 13.9V (see 3:44 seconds).

 

[luthj]

My sprinter alt runs at about 2,200 rpm at idle for example.

 

[shade]

Some interesting testing. Not enough data in my opinion, but a nice test bed.

The issue is that they are running that alternator very slowly, even at idle most alternators are seeing 1800+rpm due to pulley sizes. Not very reaslistic in my opinion.

They were seeing 87A on a 300A lithium battery at 13.9V (see 3:44 seconds).

You're on top of things. That was just posted today.

And in the end, their proposed solutions were all discussed here.

Iirc, the BMV-712 can use a temp probe. I'll have to see if that could be attached to the alternator if the battery already reports temp via the VE.Bus. My truck engine idles at around 750 rpm. For alt charging, I'd be on the move, which should help with cooling.

 

[luthj]

If it comes down to it, you can pretty easily swap to an higher ratio pulley to drive the alt a bit faster. Most alts run about 2-3x ratio.

I found the 300AH battery at 50% soc interesting. the 13.9V (pretty close to your alternator) was doing about 90A. If you go with half that for your bank, it would be 45A. I think that's a good expectation, and would be totally fine with your factory system, no extra electronics needed hopefully.

 

[shade]

If it comes down to it, you can pretty easily swap to an higher ratio pulley to drive the alt a bit faster. Most alts run about 2-3x ratio.

I found the 300AH battery at 50% soc interesting. the 13.9V (pretty close to your alternator) was doing about 90A. If you go with half that for your bank, it would be 45A. I think that's a good expectation, and would be totally fine with your factory system, no extra electronics needed hopefully.

That's the plan. Manual control of the charge disconnect will also help.

 

[john61ct]

If it comes down to it, you can pretty easily swap to an higher ratio pulley to drive the alt a bit faster. Most alts run about 2-3x ratio.

I found the 300AH battery at 50% soc interesting. the 13.9V (pretty close to your alternator) was doing about 90A. If you go with half that for your bank, it would be 45A. I think that's a good expectation, and would be totally fine with your factory system, no extra electronics needed hopefully.

The LFP bank will "pull" whatever current is "made available" by the source.

Cutting the Ah capacity size of the bank down makes no difference, just means you start damaging the bank (reducing lifespan) by increasing the relative C-rate.

The electronics between the alt and the bank to allow you to safely limit the current drawn is not optional, in a normally automated "production" scenario.

IMO the only question is, do you use a capable VR, or a DCDC?

Of course experimenting with human supervision, is a different story.

 

[luthj]

The LFP bank will "pull" whatever current is "made available" by the source.

This is incorrect. Like any battery there is some internal resistance, and voltage plays a very important role. If you have say, 14.4V with unlimited current, and no wiring voltage drops, then yes, the battery could hit 2 or even 3C charge rates at lower SOC. But in application the voltage drops int the wiring, lower alternator voltages, etc will all combine to limit charge rates.

Take a look at the video, the battery topped out at just under 90A @ 13.9v (there was some wiring voltage drops I am sure).