Idiot's guide to a self build battery

[sw25481]

I have made my way through the whole thread and it has convinced me to do what I should have done before. I gave the nice chap in China on this thread (if you have read the thread you know who I mean) the go ahead on Thursday to order my own 15 (plus a spare) 280k batteries. Turns out someone else on here is ordering at the same time and that even reduced the shipping cost a little.

I have the money, he has the batteries, what could possibly go wrong?

Firstly he sends me the option to transfer the money from my Bank account to a Sterling bank account for his company. I am sure that is 100% above board and you guys have experience dealing with him but I feel uncomfortable not using a Credit card for large purchases, especially from abroad. Section 75 offers great protection if anything goes wrong.

No problem, our friend was happy to offer payment through Alibaba Trade Assurance which is actually extra protection (or perhaps duplicate protection). I buy more than I am happy to admit from Aliexpress and Banggood so that works.

It turns out Alipay uses your Alibaba account not your Aliexpress account (who knew they were different) and mine has been locked for inactivity. Took a fair while to fight through the automated responses in the chat clients (I had to create a new account as you need a working account to talk to them on chat, which if I had I would not need to talk to them). Once I did get through a very nice and polite person (or a computer simulation so impressive I was fooled) said they totally understood, could see exactly what had happened, and would get it fixed but it could take a few days but is often quicker.

After 48 hours, I do not want to delay whoever is on this channel and buying at the same time as me (sorry by the way) so I figure, I have just created a new Alibaba account, lets pay through that. Our friend in China re-issues the request for payment to the new account (even though it is a Sunday) and I go again. Paying by Credit card through Alipay is an extra £50. I guess someone has to pay the bill to the credit card company, but I usually use Paypal and that is only £20 extra due to a promotion. I have to warn anyone that does this that using Paypal actually invalidates your Section 75 rights but I have found Paypal to be just as good at disputes (YMMV, please do not take advice from me on this). I go through the process and Paypal fails (several times over two days) with the message "Things don't appear to be working at the moment." I check the card company and they have not seen or blocked the payment. I used the card just this weekend through Paypal on Banggood to buy the BMS without issue. Paypal has a chat client but it is automated again suggesting you check you card login etc. but you eventually get to log a case and they say it will take them several hours to respond. All the online forums give advice to Web Site owners about what they should do if this error happens nothing for consumers.

Long story short. Monday and still not been able to pay for them. I hope the Universe is just telling me all good things need a little work.

[Caesium]

A bit of an unfortunate sequence of events sw25481

I used the direct credit card payment option myself and just swallowed the £50 charge. It wasn't a lot in the scheme of spending 2 grand on batteries and I wanted the Section 75 reassurance. I've never been a fan of PayPal and use it only begrudgingly when I absolutely have to. Hope you get it sorted out.

A bit of an update on my own battery situation, the second set of LF280s turned up a week ago and I've been making steady progress:



I've gone with hooking up both a JKBMS (the grey box on the front) and an active capacitor-based balancer as I found the JKBMS wasn't particularly strong at balancing; it moves 600mA at a time out from one battery then 600mA into another, so even under ideal circumstances this is only an average of 300mA of current being moved which just isn't enough to make any difference on 280Ah batteries. The capacitor board can do up to 5A (although only at very extreme voltage differences). After watching the BMS try to balance these new cells for about a day (it was doing it, very slowly, I can see individual cell voltages), I got bored and hooked up the balancer as well. Hence two wires now going to each cell.

I'm not entirely happy about the connections to the BMS though. Yes the wires are quite a lot thinner than the 25mm I have coming off the main battery terminals. About 16mm I think. But I don't think I have the means to replace those wires; my wimpy little soldering iron no way has the juice to remove those and solder on even bigger ones. So I'm debating my options at the moment. I could just try it (maybe improve those spade-screwed-to-spade joints with a butt-splice connector or something? But really both wires need to be the same size..) and monitor the wire temps. There's nothing connected to the BMS- side yet as this isn't in service yet.

The entire thing can be covered with another chunky sheet of ply once I'm done, hence the cutout in the end board. Keeps it all nicely protected and I can put stuff on top.

Previous 15S stack can be seen just behind, next job is dismantle that, build another stack identical to this one and parallel everything up.

[Stinsy]

Nice work!

I like the box and the way that you cut the sides short so that the screws can compress the cells! And I agree with the 5A balancer being required for these big cells. With perfectly-matched cells you can get away with a smaller one but the reality is that you want to keep the pack perfectly balanced and you want to deal with any out-of-balance situation as quick as possible.

I assume you're planning on building a lid for the battery box? You need to reduce the chances of any unfortunate sequence of events that ends with a spanner or other metal object falling across the terminals of the cells.

A solution for your BMS interrupting current flow is to have it control a relay. 200A 48V relays are common enough (Eg: https://www.amazon.co.uk/Current-Starte ... B07NY8Z3BP).

[openspaceman]

One thing that strikes me about this self build 28016 is that the connections and BMS-cell balancing seem simpler than paralleling up pylontech 3000s and having one master controlling the rest or am I missing something?

[nowty]

One thing that strikes me about this self build 28016 is that the connections and BMS-cell balancing seem simpler than paralleling up pylontech 3000s and having one master controlling the rest or am I missing something?

The only thing is that you have to set them up on the inverter as Lead Acid like I do as there will be no BMS connection to the inverter.

[openspaceman]

I see, is this a big problem or disadvantage compared with having a data connection to the inverter?

[nowty]

I see, is this a big problem or disadvantage compared with having a data connection to the inverter?

There is a very small chance the inverter malfunctions and wants to do something crazy and the BMS in the pylontechs senses this and shuts it down. Whether it shuts itself down or shuts down the inverter will depend on the brand / model. A malfunction is more likely to be installer error, a bit like most air crashes are pilot error.

Your taking a small risk anyway with having less protections on the new parallel bank. The biggest risk is cell balancing which is dealt with via the active balancer as long as itself does not malfunction.

There is no risk free option as a pylontech BMS "could" also malfunction.

But LFP cells are one of the safest lithium technology. Note the video below is absolute extreme abuse. I have had one mishap which was "pilot error" and the string fuse I installed in case of such error blew as designed, no drama.

[Tinbum]

One thing that strikes me about this self build 28016 is that the connections and BMS-cell balancing seem simpler than paralleling up pylontech 3000s and having one master controlling the rest or am I missing something?

Pylontech really aren't hard at all- it just a lot of people don't read the manual properly. Personally I like BMS and am planning to do mine using Seplos BMS's that i have bought already.

[Oldgreybeard]

Pylontech really aren't hard at all- it just a lot of people don't read the manual properly.

This is very true. I have watched a couple of videos by a chap that consistently condemns Pylontech batteries, and one stand out point is that he just hasn't understood the manual. He's had problems, but all bar one are because he doesn't really know what he's doing. TBH, I have some sympathy, as the manual isn't as clear as it could be, although the same is true of some of the other stuff he's not got right, which seems to be mostly Victron. I'll admit to having had to read the Victron documentation a few times to understand what I'd need for such a system and how I would need to set it up.

Of all the Chinese manufacturers, though, I think that Pylontech have probably done the best job. Their documentation isn't perfect, but it is a lot better than that for, say, the Sofar inverter I have.

The takeaway point from this ramble is that with Pylontech kit you at least have a fairly good manual. With a homebrew battery you most probably won't, and it seems few after market BMS units are that well documented, either.

This wouldn't have bothered me a decade ago, I'd have home brewed something confident that I could set it up, tweak it and fix it. As I've got older I find I now trade cost saving for trying to make sure my wife can look after things if need be. There is a lot of stuff I've replaced in this house since I started building it in 2012, not because it's gone wrong, but because only I knew how it worked, and it would be a liability if I were to suddenly shuffle off this mortal coil. A battery system will most probably last a decade or more, so it is worth thinking ahead, IMHO.

[nowty]

Ironically in the future (decade or more) I suspect I will go back to purely pylontech or equivalent because I won't want to deal with self build stuff anymore, but for the time being I am ok with it.

On the other hand, with a homebrew system there is either very little to go wrong or its obvious to fix. If I get a Pylontech alarming, its probably going down the local recycling centre.