Second small battery build

[Maxxim]

76 day ago I ordered a batch of LiFePo4 cells from Aliexpress Genuine Battery Store: https//a.aliexpress.com/_mOjK28Ln and yesturday I recieved them finally. They where shipped from China, and about 70 days later they arrived to Poland and showed up on UPS tracking. It took only a few days from there to arrive to Finland.

Have to say that this time the batteries was packed very well(even if it was free shipping). Big box with foam inside and every cell packed in a smaller box with foam. Busbars and bolt was included. The most heavy duty busbars I have seen included with these china cells. Good thing is also that they are flexible. Feels very high quality. Also got five of them so two extra for spare, very good.

The cells itself are stated 120Ah and they are brand new and in perfect condition without any damages. All mesured 3,27V. Will do a capacity test soon...

Total cost including shipping and tax was 210 euros which isn't bad.

 

[Maxxim]

Seems that the link is wrong in the first post.. here is the right one: https://a.aliexpress.com/_mK2LRQ3

The total size of the pack(4x cell) is quite compact, 195x175x180mm, quite a lot smaller than a same Ah size lead acid battery. Doing the top balance atm...

 

[Maxxim]

Made the capacity test last night with 14-15A load. Seems to be very nice batteries. No big drift in voltages and total capacity of the pack was very good 122,47Ah. Not bad at all, very happy.

Was able to test my new Victron 25A charger. Quite nice product. Speeds up the charge quite a lot compared to my old 10A china charger.

 

[Maxxim]

Seems to be a pain to find a proper box for these batteries, that isn't too big. Couldn't find anything at a resonable price. So I decided to DIY. Welded out of 2 and 3mm metal sheet. Will ad a non conductive cover with terminals.

 

[Maxxim]

Sand blasted the box and it did go for powder coating.

 

[Prefersdirt]

Great you could build your own box. I work in a welding shop - but I am not on the floor (I do office stuff). I need to learn those skills!

 

[Maxxim]

Thank you. Well, everything is possible to build, but would need some time and effort. Luckily I'm working in a place that has availability to laser cutting. I'm not so used to welding these days. Twenty years back I was welding type every day. But now only here and then... Mig/Mag welding is quite easy, no need to be a pro.

 

[Maxxim]

Got the box from the powder coating. Luckily the battery cells fitted perfectly. Did't test fit them before I took it to coating. Still need to make threads in the lid holes and a plastic lid with power terminals. Will see how I fit the BMS.. there is a bracket in the box with threaded holes, but maybe I'll just use zip ties, will see.

 

[Maxxim]

This is mybe not so interesting compared to big solar system projects here, but I'll keep on coming with small updates anyway ??

Made the lid out of 6mm styrene-acrylonitrile plastic sheet and machined power posts out of aluminium. Still have to find a very thin seal to seal up the lid.

 

[Maxxim]

The battery is ready for testing. Usage will be in a boat as a battery for a bow mounted trolling motor. Added heating pads underneath the cells, and between 0.5mm stainless plate, but didn't fit the thermostat yet. Will see if I even need heating at all..? Used 8mm foam on the walls and under the cells. Clamped the cells together with a 4mm aluminium plate so they will stick firmly in all conditions.

 

[Substrate]

Looks nice! But just a suggestion about your connections, especially in a marine environment.

Have you considered using a *light* coat of anti-oxidant to the flat surfaces of your connections, like NoAlox or Penetrox (found at home improvement stores)? Flat surfaces, NOT on the screw threads!

Reason being is for 2 things: dis-similar metal connections (copper, stainless, aluminum, steel eyelets). Dis-similar metals start to go high-resistance after awhile. It's the reason you find it in home improvement stores, mostly for older homes with aluminium wiring attaching to modern copper circuits.

Oxidation: oxygen gets into even the most tightly secure connections. A secondary benefit of a LIGHT coat of anti-oxidant on flat surfaces before assembly helps keep that out.

Sure, it will work fine this season without it. But next? And maybe the one after that leaving you stranded on the lake with all the bass laughing.

I brought this topic up before, and it seemed to go off the rails for some reason. Just a suggestion...

 

[Deleted member 23531]

I brought this topic up before, and it seemed to go off the rails for some reason.

There have been some discussions recently where Ox-Gard was discussed / explained / used with more positivity. I used it for my battery. Mine is not in a marine environment but it worked fine and didn't apparently degrade the resistance of the connection at all: I reported just a couple mV of resistance drop on the bus bar, even using a temporary low-contact-area hacked/sawed-up bus bar.

As for @Maxxim : that is a bad ass box! Nice work!

 

[Substrate]

Right on. I won't press the issue here since the usage is up to the user's need and experience.

You kind of explained exactly the reason I still use it - you got a couple mv of resistance drop on the bus bar.

In the long term for major power, not an issue, but it may confuse the cell-balancers. Ie, your cell only has 10 milliohm impedance, but now with the additional 20mv measured drop, to the balancer, it might think the cell has double the internal resistance to 20milliohm.

So not a huge deal. I got the time and the goo, so why not.

 

[Matteo B]

This is super great build, thanks for sharing!

 

[Maxxim]

An update about this battery. I has been in use for a whole fishing season(for the bow mounted electric motor) and I havn't had any issues with it. Have been workong great. It's a very powerfull pack and has plenty of capacity for this use. Can easily use it for 2-3 fishing trips without charging it between... Just doing a new boat restoration project and the battery will be in active use also in the future.

You are welcome to check out my restoration vid on youtube, more episodes will come soon.