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tiago avatar image
tiago asked

Mppt 100/50 6v battery problems

Hello,

I have two dead 6v batteries (Crown CR220, similar to Trojan T105) after just 13 months of use. According to the dealer the problem lies in the charge characteristics that are pre-set in my mppt 100/50. Charge voltage appears to be too low to fully charge the batteries, which apparently kills them over time. The Victron app however, showed the batteries going in absorption and float phase just about every single day. Which did not make me suspect chronic undercharging.

Some specifics:

2x 6v batteries 220Ah wet cell deep discharge in series (12V system) - 550 Wp solar panels - victron mppt 100/50

Mean depth of discharge ~ 50Ah/night or ~20-30% - extreme dod ~50% maybe 10% of the time - Max load normal use at night 50% of time @~9A

Charge characteristics: bulk working up to 14,2V - absorption @13,8V (I’ve now learned this is too low for those type of battery) - float @13,8V Max charge from solar ~35A. Symptoms of failing batteries: they don’t hold their charge, solar just keeps on charging in bulk (Up to 300% of normal Ah) and batteries get super hot. Extreme Loss of electrolyte.

my questions: is there a chance I am just being told off by the dealer, are 6V batteries of this type in this setup just a bad idea, or is it definitely a user error and do I need to change settings for future similar batteries? Follow up: how come the charge program shows float charge if the batteries are not fully charged?

MPPT Controllers
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1 Answer
JohnC avatar image
JohnC answered ·

Hi @Tiago

Those flooded GC2-pattern batts are generic, supplied by all major makers, and have been around for many years. I use them myself (Century brand) because I can get them at mates-rates and I know they haven't sat on the shelf for years. I've 8x in a 48V bank, and another 8x oldies in a 12V bank (these gently charged at a flat 13.5V).

I rounded up a spec-sheet for yours (is it the right one?) and the settings you're using seem fine. http://crownbatterieseurope.be/assets/TDS_CR220-HD_ENG.pdf

I use (equiv) 14.4V Abs and 13.8V Float. I've considered lowering to 14.2V Absorb, but haven't bothered, as the difference in the Amps they'll accept is almost unmeasurable. And I'm too lazy to equalize them, so a little bit each day.. :)

13 months is too short. I wouldn't buy them if I couldn't get 5 years, I hope for more than that, and usually get it.

Just one dud cell could cause your failure with both batts. It's not your fault, and your dealer is wrong. If he's holding a warranty then I'd take him to task. The ones you have now are done for.

Interesting to see your specs though. States ~5A as a transition point from Abs to Float. I'd worked out 4.5A as my 'best' spot, but then changed to 6A when a new Smartshunt showed me little difference over the day. I now boil off a little less water..

Hope this helps. Good luck.

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