DIY Lithium Guide

[nebster]

Unfortunately, Victron appears to have removed the tail-current charge termination feature, even though it's still documented. I purchased based on this documentation, and all they say now is, "you should have your BMS manage charging."

Incredibly frustrating.

[Maine Sail]

Originally Posted by nebster

Unfortunately, Victron appears to have removed the tail-current charge termination feature, even though it's still documented. I purchased based on this documentation, and all they say now is, "you should have your BMS manage charging."

Incredibly frustrating.

If this is true it's likely due to a potential liability issue. Due to the inherent inaccuracies & drift with Ah counting, relying on for SOC termination could actually become dangerous with LFP...

It's one thing to be get out of sync with lead acid, so you over charge a bit or over discharge a bit, not the end of the world, but it can actually become dangerous with Lithium.

I have many, many hundreds of hours of testing a number of Ah counters against calibrated lab grade equipment, on LFP, and in as little as three-4 cycles they can get out of whack.

I've tested the *Link-Pro, Victron BMV's, Blue Sea and the Bogart. Sadly I have yet to find any SOC gauge, for LFP, that remains accurate for more than a few cycles, that I would relay on for anything to do with SOC termination.

*I currently use a Link-Pro on my own boat. I use it as a current & voltage meter, plus quasi -Ah guidance, up to 3-4 cycles away from full. I would certainly never use it to manage the banks charge characteristics nor for any sort of accuracy in SOC.

[nebster]

Originally Posted by Maine Sail

If this is true it's likely due to a potential liability issue. Due to the inherent inaccuracies & drift with Ah counting, relying on for SOC termination could actually become dangerous with LFP...

I thought maybe the same thing, at first, except I think you have it backwards: the functionality they've removed is the tail-current termination logic, which is the "safe" way to stop charge.

In fact, when I inquired, one of the suggestions was to use coulomb-counting as the mechanism instead!

As an aside, I'll just state that the moment a geek-friendly company like Victron starts arbitrarily removing features from their products "for liability reasons" is the minute they've jumped the shark in my book. Simply typing the wrong digit into VEConfigure is enough to set an LFP bank to venting a few minutes later, so it kind of doesn't make sense anyway. I'll give them the benefit of the doubt here, except it really would be nice to know why they did this, and more importantly whether we could get the feature back.

I have many, many hundreds of hours of testing a number of Ah counters against calibrated lab grade equipment, on LFP, and in as little as three-4 cycles they can get out of whack.

Yeah, coulomb-counting is error-prone and drift is a problem. If your battery is large enough and your charge boundaries are conservative enough, I believe it can still work as the primary charge management. (I am one of the ones building in "dead lithium" to my pack, as you so artfully call it. ) But in this case there has to be a backup mechanism that monitors voltage as well, and if you have that... maybe you just end up using it instead?

[200MPH]

Originally Posted by nebster

Unfortunately, Victron appears to have removed the tail-current charge termination feature, even though it's still documented. I purchased based on this documentation, and all they say now is, "you should have your BMS manage charging."

Incredibly frustrating.

Ah, that kinda makes sense. Their documentation runs through how to setup tail-current charge termination when using the Lynx Li configure assistant in VEconfigure program.

But when I downloaded the program just a few weeks ago, and then played around with how it worked using their option of 'full featured simulated connection', the option to set tailing amp charge cut off was not in the Lynx Li configure assistant. Strange me thought...

Well thanks for the information, I guess there is no rush to upgrade firmware in my 2009 model 12/3000/120 Multiplus. Seems like only option is to tweak bulk Amp settings up or down a little to get tailing amps about right at the end of the fixed duration 1 hour absorbtion phase. But it will only be approximate, which is a pity.

Back to plan B then. Hookup up a simple voltage sensing switch across current shunt and use output from the switch as the input to the Multiplus to tell it Absorption phase is over.

I'll have a look at doing that sometime - got a few days away a sea next week on board, so hopefully can see if the idea is feasible. I guess it will depend upon accuracy and resolution of voltage switch.

[nebster]

Originally Posted by 200MPH

Seems like only option is to tweak bulk Amp settings up or down a little to get tailing amps about right at the end of the fixed duration 1 hour absorbtion phase. But it will only be approximate, which is a pity.

Yes, I also can't understand why absorption has to be specified in increments of 1 hour, minimum 1 hour. I would be much happier if the resolution were minutes and the minimum were 0 hours. I also got no answer when I inquired as to why there was this limit. It seems silly, to me.

Back to plan B then. Hookup up a simple voltage sensing switch across current shunt and use output from the switch as the input to the Multiplus to tell it Absorption phase is over.

I can't speak to your 2009 Multiplus, but the newer Quattros at least have a "DC voltage" value as a logical input to some of the assistants. It may be possible to construct in the software a similar switch. I know it will use the sense wires to give you pack voltage in this case.