Considering 16S 48V DIY build

[netw0rks]

I have a 2015 Precedent that I need to replace batteries in. I've been looking at the 105Ah EVE cells. My plan is to put 16 of them together for a nice little pack.

If I'm reading everything correctly, I'd have a 1C discharge rate of 105A and a 3C (30 second) discharge of 420A. I think that should be fine for my campground travels and neighborhood joyrides.

I know I need a good BMS. I've read that some don't like to have all the current flowing through their BMS, and some say it's fine. I want whatever is going to last. I've read good and bad things about the Dalys, so I'm not sure what to think about those. Any other recommendations?

Lastly would be the charger. I have an ERIC charger, but according to the Delta-Q site, these shouldn't be used for lithium. I have been considering the EG4 charger from Signature Solar. Any thoughts there?

Thanks for any help you can provide!

[WalterM6]

Things to stay away from. Make sure the screws for the battery connections are at least an M6, preferably a M8. As you already stated stay away from the Daly BMS, you'll never be able to balance your batteries with one. They only have 25ma balance current. 3C=315A 4C=420A. As for a BMS go for one that has a contactor inside to open the circuits not transistors. Also look at the CALB batteries before you buy the one you mentioned.

[Pat911]

Nothing wrong with EVE cells, or CALB for that matter, both are first grade cells.

Any BMS can fail, but to reduce the risk, don’t run the BMS at its limit, give it a 50% margin if possible, whether it’s contactor or FET controlled. (I would only use FET, not contactor though)

Don’t get a Daly BMS, overpriced, underfeatured and underperforming. They do look better and more substantial though. Don’t be fooled.

You’ll learn a lot building your own battery, go for it. You’ll also end up with a better battery, but you won’t necessarily save money.

Cheers
Pat.

[netw0rks]

Thanks for the replies! I have decided I want to do this, it looks like a really fun project. I will do some more research on a quality BMS.

Any reason you'd stay away from the contactor? I watched a video that stated that they are "power hungry" but I didn't really understand how that could be.

If I can find a 300-400 amp BMS that doesn't break the bank, I'd certainly prefer that, for simplicity.

[Pat911]

Your cart already has a very good contactor. You don't need a 300A-400A BMS as you can use the BMS to control the existing contactor. You only need a BMS that is large enough to handle whatever charge current you will be using, plus the margin I mentioned earlier. An 80A BMS is more than sufficient.

[WalterM6]

This example is a very good reason why you would want a contactor type BMS instead of one with Transistors/FET's. That reason is the price. A BMS with a constant 300a would cost 4 or 5 hundred dollars. Another plus is that it has 260ma balance current.

https://fr.aliexpress.com/item/10050...1790a02c30e-10

[Pat911]

True, but if you’re building your own custom battery you don’t need to pass the motor current through the BMS, it can be connected directly to the battery, with the BMS disabling the very low current key switch line to the motor controller to shut it down on a fault condition.

All the drop in solutions available pass all current through the BMS. This is done to ensure an easy, universal drop in battery. This approach is not necessary if you’re building your own and you’ll end up with a much more reliable solution if you don’t pass hundreds of Amps through the BMS, regardless of FET or contactor switching.

[netw0rks]

That makes a lot of sense Pat, thanks. I need to find a schematic of my cart. I'll do some searching.

I'm still looking for a BMS that can provide a decent amount of balance current. From what I'm reading in the solar forums (and others), I may not need a lot of balance current if my cells are top balanced and remain fairly close together under loads. I've seen that some of these "nice" BMS systems like Rec, cost upwards of $500. That's a no go.

[Pat911]

A full schematic isn’t required, just use a relay to break the wire from the key switch. Simple. On a fault, the cart will think someone has turned the key off.

I always use JBD BMS’s now, they are reliable and cheap. Check AliExpress. If you’re concerned about balance current then there’s JKbms, that has an inbuilt active balancer that can do up to 2 amps.

A properly top balanced pack will be able to be kept in check with a balance current of 200mA, but only if balance is active even when not charging. This is not possible with Daly that will only balance whilst charging.

[UncleJerm76]

Can’t go wrong with using Pats suggested components and wiring suggestions. But I can’t say I agree with not even considering a Daly BMS, guess I have a unicorn. Pat I know your Daly experience was less than ideal but my 500a Daly has been very impressive to date. I agree there are other brands with massive balance currents & even less expensive options if your not running high current through them, but I love my Dalys simplicity - and the units look nice too. As Pat mentioned oversizing your BMS is more than just a good idea, should be a requirement for your build.

As far as balance-current issues - they don’t exist for me, the Daly has been enough to keep my pack balanced during charging. I did a long top balance after I first got the cells and the Daly has maintained that without issue. Where I do see someone possibly needing more balance current than a Daly, is on used/missmatched cells that have different internal resistance OR very fast chargers that can fully charge the pack so fast they limit the time a Daly has to balance. If your buying new matched cells they simply don’t drift far enough apart to need high-current balancing. If new balanced cells are drifting that far apart after a top balance then they have internal issues, and/or you got ripped off on the cells. Normal matched cells just won’t do that.

Just my opinions from my experience so far. I would not hesitate to use Daly again on a future build. Maybe later when I’m running a silver wolf AC conversion and drawing big amps I might be singing a different song, but so far I’m incredibly happy with it.


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