Idiot's guide to a self build battery

[Colin Deng]

Hi All

As the holiday season approaches, I would also like to take this opportunity to wish you and your family a very Merry Christmas and a prosperous New Year!
May the season bring joy, health, and success to you and your loved ones.

And hope we can have a good start at the year 2025
Sun will shine on us again

Thanks
Colin

[Joeboy]

Merry Christmas & a Happy New Year to you and your family Colin.

[Colin Deng]

Merry Christmas & a Happy New Year to you and your family Colin.

Thank you Joe for your kindness
The same to you ~

[Fintray]

A merry Christmas to you and your family Colin and all the best for the year of the snake.

[Joeboy]

I noticed over Winter that if the battery stack had taken a beating I couldn't get it back up to 100% soc within the 6hr window. I thought an extra DC charger to piggyback would be a good idea.

With the stacks being 15S I couldn't find a charger to hit the correct voltage. Everything I was seeing was 14S or 16S

I erred on the side of caution and went for a 14S rated to 50.4V. The idea being that the 50.4V charger will work in parralel with the Goodwe up to 50.4V and then cut out leaving the Goodwe to finish the charge.

With luck, the 50.4V unit will have supplied enough juice at the start of the nights charge for the Goodwe to get it up to 100% soc.

Now wondering if there is a risk of damage to the new charger as in the Goodwe charging cycle it will be exposed to 55V as the Goodwe ramps up to the higher soc's. I had been going to wire the DC off the new charger onto the central bus bars and let er rip. I had thought that the 50.4V charger would just stall at or around 50.4V but hadn't given any thought to the extra few Volts it would see. Anyone else done this or similar?

It's a big bit of kit and as luck would have it fits nicely alongside the ASHP garage CU and the cables are perfect for where I'd like to connect to.

I don't think I'd blow the arse out of it with a few extra Volts but not knowing? Would this be a blocking diode moment?

[Joeboy]

I've sent a mail to the nice man in China asking if being backfed 55V would be a problem.

[Marcus]

I suspect the main issue would be if it has an overvoltage protection circuit which kicks in if the output exceeds nominal by a few %. If it just goes into fault mode and needs turning off and on to reset, that may not be a problem: - it's already done it's job by the time it faults out.

A blocking diode would stop it charging the battery 0.6v lower than its 50.4v, but should work. Or use an 'ideal' diode, but that adds an extra circuit to go wrong.

[Joeboy]

I suspect the main issue would be if it has an overvoltage protection circuit which kicks in if the output exceeds nominal by a few %. If it just goes into fault mode and needs turning off and on to reset, that may not be a problem: - it's already done it's job by the time it faults out.

A blocking diode would stop it charging the battery 0.6v lower than its 50.4v, but should work. Or use an 'ideal' diode, but that adds an extra circuit to go wrong.

Good thought Marcus, the beauty is that it will turn on again if power cycled. IE , cycle power and it spools up with no.finger intervention required. This bodes well for the hive plug schedule control. About 2.5kW max draw if I remember correctly. Tbh, I can't remember so will see how it's wired for output later on. 9 months to go before it's really needed!

[Joeboy]

Great answer from the nice man in China "can't".

Had a look about and this looks like it will work. I bought the built unit rather than the diy board.

https://www.aliexpress.com/item/1005008 ... ry_from%3A

Ideal isn't it?

Thanks Marcus. At 100A and with 4 chips to distribute heat it shouldn't trouble the 30A rating of the charger. at 0.2V loss max i'll be down to 50.2V for a cutoff but that's ok as that's about 80% soc going on Nowty's crib sheet.


Anecdote time. Batteries took quite a kicking yesterday and up Into the late evening. So much so that we only got to 94% soc by 05.30hrs this morning. Not a problem as its a glorious day but in Winter that would be the start of a downward trend if I couldn't get a slot.

Also noticed that when the Goodwe Hybrid inverter shows 100% soc in the Pylontechs it continues to charge for another 90 minutes as the Pylontechs feed the LF280's until balanced. This wee golf cart charger should take care of that....Or release magic smoke 1st time out.

[Richard77]

This is starting to sound like a del monte advert!