Lithium in a 12V dual Battery System

I have a DIY lithium battery with LBSA BMS 120A 4S 12V from LBSA and want to plug it into my National Luna Dual Battery system on the bakkie. I think the BMS will be fine but want to confirm this.

Any thoughts on the LBSA BMS and its ability to handle the connection… I also have seen alot of mention of the alternator and its (in)ability to handle the load of charging the battery.

Thoughts and suggestions please :wink:

I think the voltages swings from an alternator will drive that BMS nuts. The vehicle voltage changes anything between 13V an 14.7V as the rpm and other loads changes

I do have a large starter battery which I think will smooth the voltages for me but that’s where I’m unsure… The lithium will only be connected after 2 mins of the vehicle running.

Alternator is a 90a model so pretty big…?


Ok, maybe show a practical example in my Hilux. I have a dual battery in that one. When I start it and it idles from cold, it sits around 900rpm and alternator gives around 14.2V. Driving around, alternator gives around 13.8V. When coming to a stop with engine warmed up and engine at 700rpm, voltage might go down to 13.1V, this is with a 120A alternator. I can see this on a digital display I had fitted as I suspected an alternator issue in the past. It does show that the alternator does not keep a steady 14.4V as many people assume. Also, bear in mind that automotive environments are brutal; with temperature swings way outside what lithiums like.

I’m not trying to dissuade you, just highlighting what I’ve seen on my very own vehicle’s dual battery system

PS, that is not to say lithium’s are unsuitable in automotive use: my previous M3 came with a factory lithium battery. But in the case of BMW, they’ve gone the route of a PWM signal coming from then engine DME driving the alternator’s regulator. In that case the voltages in the car are a lot more stable. But to do that there’s a lot of complexity involved by using feedback to regulate the alternator based not only on rpm but load as well. Also, the battery pack is in the boot, not in the engine bay

Thanks @gbyleveldt
Thats what got me starting the thread… the best solution is a DC DC solution like the Victron Orion.

It’s not a huge issue as I can swop out the Lith for the LA I had in the box and still charge the Lithium on a charger and solar.

Thanks for feedback!

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What amps do you need to charge the battery at?

Just for interest sake, where did you measure this? Before or after the regulator. The regulator is suppose to take care of the varying voltage caused by rpm differences. And then, the battery should act as a very big voltage stabiliser as well.

This is directly off the 2nd battery, the meter is mounted inside my bakkie so I can see that the battery controller is switching on (and if I blew the fuse between the batteries). That 2nd battery powers the search lights on my jackal chair, sometimes I run it a little long haha

On most vehicles the regulator is a pretty crude device, so such voltage swings isn’t unusual.

I see the Orion has 2 models. 12/12 30A and 12/12 18A.

Not going to happen just yet… No bucks… :wink:

True. But the amperage of the alternator is also RPM dependent (those manufacturing penny-pinchers aren’t going to make it any bigger than they absolutely have to). At low RPMs the amperage may not be high enough to raise the battery voltage, so the regulator doesn’t even come into play. This is certainly my observation as well, that at idle the voltage doesn’t quite rise up all the way to 14.4V or 14.5V, it may only reach middle to high 13s.

Sooo… :wink:

My questions still stands… the BMS is spec’d to handle 120A discharge and 60A charge so do I need something like an Orion between the 2 batteries given I have a large LA as a starter battery…

I have emailed LBSA but no response so far… followed up again today.

I would say yes. For several reasons.

  1. Fault conditions. A fault in the lead acid battery will see the LFP battery dump large amounts of current into the lead acid battery. Of course you will fuse against this sort of thing, but this is the main reason the manufacturer will tell you not to parallel the two chemistries. At least BlueNova tells you that.

  2. Different charging voltages. Sure, they are close enough that it probably doesn’t matter. So this is probably the least of it.

  3. Different impedances. The LFP battery will absorb most of the charge, and only when it is full and the voltage starts to rise will the lead acid battery start getting a decent charge. You will almost certainly separate the batteries while the engine is off (you don’t want to run the starter motor from the LFP battery, right?), but that means that whenever you start driving again, if the LFP isn’t full, the starter battery is not getting recharged until the LFP is full. That can leave you stranded. You want it the other way round: recharge the starter battery first.

  4. Potentially burning out an alternator. Again, those bean counters at automotive central don’t make that alternator any more smart than it has to be to charge the battery the car came with. Lead acids plateau quickly and the charge current drop off, so the charge current tends to drop off before things get hot. Not the case with LFP. Charge current stays high all the way up to 98% before it drops off. A deeply depleted LFP can overheat an alternator. Granted, even with a DC/DC charger, it may be necessary to manage this.

So for myself, I’d use either a DC/DC converter, or a second alternator. Or put a PV module on the roof and charge only with that.

Thanks @plonkster. I’m risk averse so that’s the plan… even a small Orion will do it… I have solar to charge it as well as a IP65 12/15 Victron charger if needed.

Thanks all

Reminds me of this video …

Which brings me to this:

Reason I’m interested is because I got a 12v/500VA MP in a deal with 4 x 100ah lithium cells from Zimbabwe. Yeah, no jokes, trading with Zim is easy if you have Zim people organizing it.

This is for camping … so either I get a MPPT and a panel and a BMS or I get the batts charged whilst one drives.

Nice thing with my Isuzu is that I can adjust the revs when idling … but still, waiting at a robot idling at 3000rpm, the alternator in that engine compartment where the exhaust manifold gets to ±1000 degrees, naa, don’t think so.

First alternator lasted wot, 18 years, the 2nd one won’t last a year with lithium charging…

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More like 300°C under no load. But yeah, still plenty hot.

Interesting topic this, btw. You want lower exhaust gas temperatures because higher temperatures are 1) bad for the Turbo, if you have one, 2) increases temperature of the charge air from the Turbo, and 3) causes formation of Nox.

That’s what EGR is about (among others). Put some inert Carbon dioxide in there to lower the combustion temperature.

It is also what Dieselgate was about. VW figured out that you get better fuel consumption if you allow for a bit more Nox… the regulators did not agree. What is particularly confusing is that doing this conveyed no real pre-sale benefit: The numbers on the advertising material would be the as-tested numbers… the worse ones.

Aaaanyway… derailing threads as usual.

Was the issue with dieselgate not rather the emissions than the fuel consumption (guess the two are somewhat interrelated)?

Yes, it was the emissions. Specifically, the cars made more Nox (Nitrous oxides) than allowed. And this happened because VW had a “cheat” built into the ECU, so that when it detected that it was being tested, it would run a different set of values. When tested, it would then produce nice low Nox values, but with slightly more fuel consumption.

The weird part of it all, is that they would not be able to use the lower fuel consumption number in advertising or for tax purposes. So essentially they made a car that would be “better than advertised” and the owners would only discover this after the car was already sold… which makes you wonder what happened. Did some engineer just stubbornly refuse to give up on the gains made in fuel consumption, and insisted on putting it into production despite those whining ninnies at the environmental agencies? :slight_smile:

So yes, your guess is correct. The two are interrelated. Newer diesel engines are actually heavier on fuel (than they need to be) in order to make less Nox.

Same thing actually happened to Petrol engines. It was perfectly acceptable to run petrol engines lean at low loads and part throttle, leading to better fuel economy when cruising. No longer, since lean mixtures makes more carbon monoxide.

It gets even more interesting. Even though a lot of effort goes into not running an engine lean… the opposite end has less of that. When running at full load, many many ECU’s skips the whole closed loop oxygen sensor feedback stuff and just goes open loop “gooi mielies” mode, ie it makes the mixture rich. Safer for the engine (a rich mixture runs cooler). From what I’ve read, Tata is one of the few manufacturers who doesn’t do this…