Idiot's guide to a self build battery

[Joeboy]

Why don't we organise a group buy with collin, but on the proviso he gets paid only when one of us has quality tested the cells in the UK and they pass.

We can then take the cost of the cells + the import fees + time for the UK testing and divide by the group buy.

That doesn't work as in any transaction the goods need to be paid for. Also better doing it on your own, unless another member lives close by to you and its a split delivery. Otherwise it will grow arms and legs with multiple people. I understand the trepidation, was there myself. I don't think you get much better than this though....

[Oldgreybeard]

Why don't we organise a group buy with collin, but on the proviso he gets paid only when one of us has quality tested the cells in the UK and they pass.

We can then take the cost of the cells + the import fees + time for the UK testing and divide by the group buy.

That doesn't work as in any transaction the goods need to be paid for. Also better doing it on your own, unless another member lives close by to you and its a split delivery. Otherwise it will grow arms and legs with multiple people. I understand the trepidation, was there myself. I don't think you get much better than this though....

I very much agree, years ago a bunch of us into electric bikes organised a group buy of Headway LiFePO4 cells from China. Turned into a complete and utter nightmare, and didn't really save much money, either. The margins on batteries isn't that big, at least for resellers in China.

[Swwils]

If there is no need to safeguard against bad cells then all is well.

I wouldn't mind keeping a UK stock if people are interested.

[Krill]

If there is no need to safeguard against bad cells then all is well.

I wouldn't mind keeping a UK stock if people are interested.

Whilst that could be profitable for you that would be one hell of an outlay...OTOH is the worst case scenario you build a giant battery for yourself.

Actually, what's the largest battery one could put together out of those 280Ah cells?

[Swwils]

Have you thought about adding tempeature monitoring to your DC terminals / busbar?

The pylontechs feature this behind the Amphenol surloks.

[Colin Deng]

If there is no need to safeguard against bad cells then all is well.

I wouldn't mind keeping a UK stock if people are interested.

Whilst that could be profitable for you that would be one hell of an outlay...OTOH is the worst case scenario you build a giant battery for yourself.

Actually, what's the largest battery one could put together out of those 280Ah cells?

It based on the space you have for the battery
You can put 16S2P, Most customer would want it
And i have seen a customer doing the 16s4p for the battery system
It will be large..

[Oldgreybeard]

Have you thought about adding tempeature monitoring to your DC terminals / busbar?

The pylontechs feature this behind the Amphenol surloks.

It's useful to know out of interest, but I don't think it really matters for a relatively large battery, that just isn't going to change in temperature by more than a few degrees. It probably makes sense to do this for a smaller battery, being worked much harder, perhaps.

I've been plotting the temperature of our six Pylontech US3000C's and it barely changes. For example, the plot below is the reported temperature from the packs over the past ten days (ignore the two spikes, they are MQTT glitches):

Battery temperature.jpg (38.63 KiB) Viewed 1226 times

Even in the summer the battery never really got warm, it pretty much follows the ambient air temperature and doesn't change by more than about 1°C when charging or discharging. With the high capacity of these home made packs I doubt that charging or discharging a pack at a few kW is going to have any significant effect, TBH.

My experience with LiFePO4 cells in home made bike batteries was that they only started to get slightly warm when charged or discharged at over about 1.5C. For a single stack of these 280Ah cells running with a 3kW inverter/charger they are only going to charge/discharge at around 0.23C, which is a very low rate. Even with a 5kW inverter/charger they are still only going to be charging or discharging at about 0.37C, which is still very low.

Best bet might be to just check them with an IR thermometer after a sustained period of charging on a hot day, and if they aren't much higher than ambient then I'd be inclined to just not bother with monitoring. Probably a good idea to check the temperature of every high current connection every now and again, in case one comes loose and overheats, but I'm not sure that risk warrants fitting lots of sensors and rigging them up to some sort of warning system.

[Lincs Robert]

To be clear, Colin is shipping these cells using DDP.

DDP it stands for delivery, duty paid. This means that he/they are taking the commercial risk of shipping to your door, with all duties etc paid.

The International Chamber of Commerce has a set of commercial terms & conditions for international trade around the world. These are called INCOTERMS. DDP is one of many. Google and all will be revealed. Welcome to the world of international trade. Many large organisations employ shipping clerks who deal with this stuff day in day out. I’ve dealt with it a bit and believe me, DDP is the one to go for, many others are a world of pain & only worth going for if you are shipping large quantities. What we are doing is the smallest of toes being dipped into a very large body of water.

Rob

[Oldgreybeard]

DDP makes life a great deal easier, IMHO. I've noticed that other overseas suppliers are doing this now, last two orders from Aliexpress have been DDP, much, much easier than having to pay the, often extortionate, customs and duty "handling fee" charged by companies like UPS and DHL.

[Joeboy]

To be clear, Colin is shipping these cells using DDP.

DDP it stands for delivery, duty paid. This means that he/they are taking the commercial risk of shipping to your door, with all duties etc paid.

The International Chamber of Commerce has a set of commercial terms & conditions for international trade around the world. These are called INCOTERMS. DDP is one of many. Google and all will be revealed. Welcome to the world of international trade. Many large organisations employ shipping clerks who deal with this stuff day in day out. I’ve dealt with it a bit and believe me, DDP is the one to go for, many others are a world of pain & only worth going for if you are shipping large quantities. What we are doing is the smallest of toes being dipped into a very large body of water.

Rob

Nicely put and a large part I think of people's trepidation in long distance purchase? Certainly my set arrived with no further duties to be paid.