Lithium batteries

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markcraven
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Re: Lithium batteries

Postby markcraven » Thu Oct 22, 2015 4:38 am

Having done a bit of reading around this in preparation for my eventual upgrade to lithium, you might find this article useful. It seems to prove a lot of the lithium DIY experts on some of the Oz forums were actually right about the charge voltage settings.. You don't appear to lose much capacity at the lower and safer charge voltages.

www.powerstream.com/lithium-phosphate-c ... oltage.htm
http://www.facebook.com/blackboxelectricalengineering
http://theminimal2.blogspot.co.nz

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Re: Lithium batteries

Postby Nut17 » Thu Oct 22, 2015 7:51 am

And after three and a half years I agree with those findings. I am now using 13.5v as my cut off during the bulk charging regime. Float and absorption modes are set to the same value. I am no doubt losing some capacity, but with 600AH this is not an issue. Cell balancing ceases to be an issue if this lower terminal charge voltage is adhered to. I have yet to discharge this bank below 50% so the opportunity to accurately gauge the loss of capacity by using the lower voltage charge protocol has yet to occur.
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Teardrop

Re: Lithium batteries

Postby Teardrop » Thu Oct 22, 2015 8:05 am

Thanks Mark, I have been doing a bit of reading lately and getting the impression different chemistries can make quite a big difference. Our Votronic charger in the Teardrop van has a lithium setting at 14.6 volt charge and 13.8 volt float. I cannot alter it. It also has an alternate Li setting of over 15 volts charge voltage. When I rang AA Solar, they advised some Li batteries need this??? The article you linked to suggests otherwise, so there is some variability in information out there.

The specs for the Valence lithium are here:

http://www.cleanenergybrands.com/shoppi ... g_12_2.pdf

From the graphs, I interpret that the difference in available SOC between charging at 14.2 and 14.6 volts would be just over 10%. Have I read this correctly? If so, I have about 180 amp/hr available capacity at 14.2 volts (there are two at 100 amp hr) which gives me about 140-150 amp hours of usable capacity, giving a bit of a safety margin. On reflection, I think this still compares very favourably with 200amp/hr AGM batteries.

The batteries are designed to be controlled by a BMS, and have cables to link with a Can bus system. I am not going to go there. But I think I will put in a VSR to stop any discharge at a pre-set voltage - thinking about 11 volts at the moment. Not sure whether to do the same about overcharging voltage, instead hoping the controllers will do their thing, along with a bit of vigilance. Anyone any ideas on that?

Cheers, Dene

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Re: Lithium batteries

Postby scubadoo » Thu Oct 22, 2015 1:18 pm

Teardrop wrote:... From the graphs, I interpret that the difference in available SOC between charging at 14.2 and 14.6 volts would be just over 10%. ...

Dene

FWIW
14.1V will rapidly fully charge my battery pack.
At 95% SOC my 300Ah pack will continue to alternator (14.1VDC at the battery regulated) charge at c70A until virtually 100% full.
That takes about 10 minutes!
If I then up the charge voltage to 14.6V, the pack will reach 14.6V and c2A within a minute. i.e. No real ability to further increase the capacity. 120% would be nice. ;)

14.6V is totally unnecessary for my situation, serves no useful purpose and is probably heading dangerously towards cell imbalance, overcharging, heating, bulging etc. I am not prepared to maintain that for very long.
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Re: Lithium batteries

Postby Teardrop » Thu Oct 22, 2015 4:35 pm

Thanks Neville, I used the Victron MPPT to initially charge the battery at 14.2 volts, then when completed put the Redarc BMS on charge with AGM setting of 14.4 volts. You are correct, it does not take much longer. I will time it next time.

I wonder whether the Votronic Li charge voltage of 14.6 was what caused a cell to fail on the original lithium battery pack I had in the little van. The importer has given me two replacement cells (one spare) but I also noticed a slight bulge on the cell sides of the original. This suggests overcharge at the Votronic's lithium setting, but the importer says it will not have damaged the battery capacity. It is a good reminder to be very careful when charging lithium. So I have a spare 100 amp hour lithium battery with a cell balancing BMS to get rid of now. Plus two 100 amp hour AGM hybrid batteries in excellent condition.

Cheers, Dene

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Re: Lithium batteries

Postby NeilV » Thu Oct 22, 2015 9:43 pm

How much for the AGM's Dene? :D

What makes them 'hybrid' too??
8.5m 1990 Dennis Dart bus, 6L turbo -4 pax
- 24v system: 2x 104ah AGM, 20a PWM controller 500W solar; 1200w puresine inverter
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Teardrop

Re: Lithium batteries

Postby Teardrop » Sun Oct 25, 2015 7:45 pm

Hi Neil. Sorry been away. Putting them up at $100 each. Three years old. Well maintained. Neve below 60% SOC. Hybrid between AGM & Gel as discussed in a recent thread.

Cheers Dene


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