Idiot's guide to a self build battery

[Stinsy]

Given that a balancer costs £50 I don’t understand why you wouldn’t fit one from the off?

[Jinx]

Thanks Nowty, I did have in mind to not run them too hard, at least until I see how they are responding. I’m thinking of manually balancing on say a monthly basis but will see. I do have a Generex 12v BMS (passive) so could monitor 4 cells at a time and compare across the pack just to keep an eye on any large imbalances.

Stinsy, can you get a balancer to do 6 packs parallel for £50? If so I will consider but if only for single strings that’s £300 for a battery that costs nothing and can potentially be simply replaced. When I looked I saw the Daly/JK etc at over £150, I assume per string and it just doesn’t make sense in my situation.
I think if you’ve paid for expensive high capacity cells it does make sense.

[Caesium]

One improvement I'm making to my packs at the moment is the addition of some carbon conductive grease. In my case "MG Chemicals 846-80G Carbon Conductive Grease", readily available on Amazon. Apparently there's a better one, same company but 847, but it was a bit expensive for my tastes (this one is already expensive enough)

So why? Well given my extensive logging of individual cell voltages I noticed that some were criss-crossing over, that is to say, for example, cell 1 would be the highest when charging under high current (don't laugh, by high I mean 50A or so), but then as the current dropped, cell 2 would rise above it, and cell 1 would drop away. This happened for a few different cells at varying times. These voltages are measured by the BMS via the ring terminals at each battery positive post over the bus bars.

Investigating further, I saw fairly significant differences in voltage between measuring on the top of the screw-post attached to the battery, and my busbars - up to 20mV under high current. Not all of them though, some of them only 3-5mV at the same current. The problem is they're all different and these different resistances are telling the BMS lies; the voltage the BMS (and therefore balancer) is seeing is not correct, so it's making the wrong decisions about when to do cell balancing.

The fix is to improve the connections. The thinnest smear of this grease on the bottom side of the busbar, then placed over the terminal, has reduced these voltage differentials to less than 1mV even under high current. Result. I did a couple to test yesterday and then monitored the voltage difference at various times, and its much better. So this translates to better readings on the BMS, less resistance in the connections, less heat generated, less power wasted!

Going to do the rest of them today. The tinkering never stops

Oh and I bought some second hand panels, I'll maybe start a thread for my ground mount I'll be building later this spring

[nowty]

Thanks Nowty, I did have in mind to not run them too hard, at least until I see how they are responding. I’m thinking of manually balancing on say a monthly basis but will see. I do have a Generex 12v BMS (passive) so could monitor 4 cells at a time and compare across the pack just to keep an eye on any large imbalances.

Stinsy, can you get a balancer to do 6 packs parallel for £50? If so I will consider but if only for single strings that’s £300 for a battery that costs nothing and can potentially be simply replaced. When I looked I saw the Daly/JK etc at over £150, I assume per string and it just doesn’t make sense in my situation.
I think if you’ve paid for expensive high capacity cells it does make sense.

I run a single simple balancer (similar one that most use) on 5 strings by parallel'ing up all the cells.
Some info about it on my battery thread here,
https://camelot-forum.co.uk/phpBB3/view ... =10#p12984

[Stinsy]

Stinsy, can you get a balancer to do 6 packs parallel for £50? If so I will consider but if only for single strings that’s £300 for a battery that costs nothing and can potentially be simply replaced. When I looked I saw the Daly/JK etc at over £150, I assume per string and it just doesn’t make sense in my situation.
I think if you’ve paid for expensive high capacity cells it does make sense.

You just link every cell to its partners in other strings rather than just the end ones. You only need super thin cables to do this because you're only expecting an Amp or two (some people used fused links incase something untoward happens).

You then need a simple 16S balancer like this one: https://www.ebay.co.uk/itm/195421030083.

[Jinx]

That’s useful info gents, I genuinely thought I’d need one per bank

[Jinx]

Made a start today, got a bit of tidying up to do yet and the hardest part of the job to come, the energy meter, but it’s now running a few items over night with manual control…

[Tinbum]

Got a delivery of 16 parcels from DPD this morning.

Thank you Colin.

Only opened one box to have a look;

barcode reads;

Manufacturer:
EVE Power

Product Type:
Battery Cell

Battery Type:
LiFePO4

Nominal Capacity:
280Ah (LF280K)

Nominal Voltage:
3.2V

Production Date:
22/May/2022

Manufacturer Website:
https://www.evebattery.com

[MrPablo]

Looks like our cells were on the same boat Tinbum, DPD should be here within the hour with 17 cells.
I need to get moving and finish up the prep for hooking it all up.

[Colin Deng]

Got a delivery of 16 parcels from DPD this morning.

Thank you Colin.

Only opened one box to have a look;

barcode reads;

Manufacturer:
EVE Power

Product Type:
Battery Cell

Battery Type:
LiFePO4

Nominal Capacity:
280Ah (LF280K)

Nominal Voltage:
3.2V

Production Date:
22/May/2022

Manufacturer Website:
https://www.evebattery.com

Thank you for the kind feedback
Waiting for the finished build!