Can EpEver 24v 40A mppt maintain 12 x 225Ah batteries short term?

[Audley A]

I was wanting to get started with a small solar set-up which would connect full time to my internet and cable, a tv and a couple of lights so that we could function fairly normally during a power outage. Someone upgrading their system has now given me (for free) 12 Trojan T105 RE batteries. These were used in 3 strings of 24 volts. Not sure how old they are but they have been sitting for 2 days and the voltage of each varies between 6.33 and 6.4x today. Can I maintain these initially with my EpEver 24v 40 amp mppt? I am buying some number (4?) of 265 watt panels.

Initially I was thinking of using the best 4 batteries and discarding the rest but now a 48 volt hybrid system beckons. I would set up a relative with the remaining 4 batteries and the EpEver. I am at about 18 degrees latitude and would now use an Outback mppt charge controller.

[Sunking]

Sure give it a try. If you want to know how old the batteries are is easy peasy, just read the date code stamped on the battery NEGATIVE term post. It will be a two alphanumeric code of one letter (A-L) and one number (0-9). Example B6. B is the month (November), and 6 is the year 2016 or 2006

Trojan Battery Date Code

FWIW the battery cores are worth roughly $25 each on a trade-in

[Sunking]

Sure you can, hook them up 4S3P. To determine the batteries age just look at the date code stamped on the battery NEGATIVE TERM POST. It consist of one Letter (A-L), and one Number (0-9). Example B6 is February 2016. They do it that way to confuse Communist and Democrats.

[Audley A]

Thanks for the reply. But now you've gone and broken the code for us Communists and Democrats. G2 means July 2012 - over 6 years old. If I can nurse them for a year depleting them on average 20 - 25% daily, I will be happy. You keep saying that people almost always destroy their first set of batteries so hopefully this will be my learning set. Initially I plan to fully charge each bank of 4 before I parallel the 3 banks.

The panels available to me now are 270w 24v (nominal 38v, operating 31v). The EpEver is rated at 100v 40 amp so if I went with six of these 3S2P, I expect that the controller would use as much as possible and disregard any extra power that may be provided at peak sun times.

[littleharbor]

3s2p will overvolt your 100 Voc. controller. Voc. of 38 volts x 3 is already 114 volts, higher still on cold, clear mornings. You need to wire 2s3p and fuse all 3 strings at the combiner.

[Audley A]

Ok, thanks littleharbour. I was thinking that the amps would be too high using 2S3P. Maybe I should stick with 2S2P or find a somewhat smaller panel.

[Sunking]

I was thinking that the amps would be too high using 2S3P. l.

Current does not change.

[Mike90250]

> 24v 40A mppt maintain 12 x 225Ah

That's 675Ah @ 24V ( 3 parallel strings of 4 ? ) The min starting point would be 67A of charge.

If you only do slight discharge, that the solar can replace in half a day, you could be OK Deep discharge, you are in trouble.

[Audley A]

Yes Mike, the idea was just to maintain the batteries with the 40A CC until I got a proper system set up. So 2S3P would be 6 x 270W = 1,620 panel watts. 1,620

[Audley A]

Not sure what happened above but the idea was just to maintain the batteries with the 40A CC until I got a proper system set up. So 2S3P would be 6 x 270W = 1,620 panel watts. 1,620

[Audley A]

Sorry but the post is truncating. Will try again tomorrow.

[Mike90250]

As long as you don't pull much out of the batteries at night, you will be able to recharge them OK

as for truncated post's . It's the apostrophe usually, from a phone or a non-standard computer. A browser with standard fonts work's just fine

[Audley A]

Trying again. The idea was just to maintain the batteries with the 40A CC. So 2S3P would be 6 x 270W = 1,620 panel watts. 1,620/ 24 = 67.5A which would seem to be too much using the 40A EpEver but at $0.45 per watt, I may go with the 6, having 3 with easterly and 3 with westerly orientation. Actually 4 x 270 = 1,080W and 1,080W/ 24V = 45A seems to be more than what is useable but system inefficiencies will probably lower that figure. Hope I'm on the right track here.

Eventually I expect to go with a 48V 225Ah set of batteries with 6 or 8 panels but right now since I already have the EpEver, I figure that I may learn a bit experimenting with the 24V system and a small load.

[littleharbor]

Trying again. The idea was just to maintain the batteries with the 40A CC. So 2S3P would be 6 x 270W = 1,620 panel watts. 1,620/ 24 = 67.5A which would seem to be too much using the 40A EpEver but at $0.45 per watt, I may go with the 6, having 3 with easterly and 3 with westerly orientation. Actually 4 x 270 = 1,080W and 1,080W/ 24V = 45A seems to be more than what is useable but system inefficiencies will probably lower that figure. Hope I'm on the right track here.

Eventually I expect to go with a 48V 225Ah set of batteries with 6 or 8 panels but right now since I already have the EpEver, I figure that I may learn a bit experimenting with the 24V system and a small load.

Here's the EP chart showing Maximum allowable wattage input for their controllers. The 40 amp number is the maximum output of their controllers.

EP max panel power chart.jpg

[SunEagle]

Wow the Max PV array wattage for the 40A is 3 times the rated power at either battery voltage. I am presuming they are figuring a low efficiency factor for their CC to work.