Daly BMS question

[mannydantyla]

I have this 100a 20s 72v BMS made by DALY. I bought it on Amazon and it shipped to me with no instructions, no literature, no nothing. Not even any packaging except the cardboard box that Amazon packed it in.

I'm using it for a 20s2p li-ion battery pack that I'm building out of used LG Chem pouch cells from batteryhookup, and the battery pack will power a small motorcycle that I'm converting to electric. So far so good but I have just a few quick questions that I just want cleared up before I start wiring up the battery pack:

1. It has a common wire for both the charger and the discharge. Can I wire the charger and the discharge wires together in parallel? Or do I need to have them seperated by a switch or a diode or something?? The wiring diagram in the Amazon listing shows the charger and discharge wires as seperate plugs that would plug into the battery back but not at the same time. But if I can I would like to have the charger onboard with the battery pack and permanently wired to the bms.
2. It has over-current protection (right?). What happens when this kicks in? Will the BMS throttle down the current a little? Or will the bike just suddenly lose all power? And if so, then what happens next? Does it stay off for a few seconds and then turn back on, or do I need to plug it into a charger or something??

Thanks!!

 

[john61ct]

Someone with experience with these specific models may (hopefully) come along and contradict me.

You are supposed to buy a big enough ampacity so that in normal operation

including unreasonably continuous WOT going up a hill with a heavy load and a headwind

your controller will not ask for more than what the BMS can handle

with a real-life margin (not trusting nameplate ratings from chinese gear, ever)

of say 15-20% for safety, or more for circuit longevity.

The controller does the current limiting itself and with a good one that factor is adjustable.

Most BMS simply burn otherwise, so an appropriately sized & tested fuse to protect it would be a good idea.

I suppose it is possible that expensive BMS have some MCU and shunt to self-monitor the battery current and shut themselves down as OCP, but I haven't worked with any that do that myself.

I have never heard of any that do true "active current limiting"

other than shutting down (latching type, needing a reset)

as in allowing continued operation. That really is the job of the controller, or a "meta" add-on like CAv3.

_______
The charge & discharge circuits / plug (s) are just paralleled on common-port designs, they would not be used concurrently, but if they were, the battery would just get the "leftover" current if any, or help to supply the load if that was pulling more than the charge source supplied.

I would not hard-wire anything, you may want another more powerful charger available, or decide to get a second newer pack before scrapping the old one.

Personally I think the BMS should be easily removed or replaced, often they fail long before the cells wear out, becomes the point of failure don't trust it too much can become a Battery Murder System rather than protection.

You will want to verify its accuracy, check cell balance with a known accurate DMM, maybe use a better balancer when the pack gets worn etc

 

[markz]

Your controller/ESC will ask the battery for whatever the controller is rated for.

If your controller/ESC is 48V 20A the controller will try to pull 20A no matter what your battery is, depending on your throttle position. Obviously at wide open throttle, your controller will be asking for the full 20A from the battery, if half throttle then the controller will ask for between 8-12A. If your battery has a BMS with 15A, your controller will trip off your batteries BMS to reset every time you ask for more then the 15A, depending on your throttle position. Is that healthy for the BMS to trip off countless times, probably not but then again depends on the quality of the bms and who really knows what the quality of a bms is unless you know for a fact its quality because you purchased from a known source and not some random dude off of ebay or alibaba or amazon.

expensive BMS have some MCU

Dont assume that just because its expensive that is a good BMS, or that its of any particular quality unless you know for a fact the BMS is good quality because you purchased from a known entity and not some random dude off of ebay or alibaba or amazon.

I bought it on Amazon and it shipped to me with no instructions, no literature, no nothing. Not even any packaging except the cardboard box that Amazon packed it in.

And your willing to trust your battery to that? no instructions, no literature, no nothing. Sounds completely and utterly sketchy to me.

 

[john61ct]

Your controller/ESC will ask the battery for whatever the controller is rated for.

If your controller/ESC is 48V 20A the controller will try to pull 20A no matter what your battery is, depending on your throttle position

No, it is the throttle + **motor** that pulls current.

The function of the controller is to regulate that demand.

expensive BMS have some MCU

> Dont assume that just because its expensive that is a good BMS

No but what is certain is, a cheap one will not have that particular functionality

I bought it on Amazon and it shipped to me with no instructions, no literature, no nothing. Not even any packaging except the cardboard box that Amazon packed it in.

> And your willing to trust your battery to that? no instructions, no literature, no nothing. Sounds completely and utterly sketchy to me

That is completely normal for cheap chinese units, also for the seller to have no clue, nor access to anyone with decent English.

Decent documentation in English is rare as hen's teeth, and such units must by definition cost a lot more, the companies producing the cheap stuff have no interest in catering to demanding DIY foreigners, we aren't even 0.00001% of their market.

Somehow thousands of forum members manage to adapt just fine, peer to peer assistance is what forums are for.

 

[mannydantyla]

Alright thank you guys very much.

The BMS is rated for 100amps continuous. I have a 4kw QS motor that will be doing ~55 amps continuous (72 volts). My battery pack can do about 60 amps continuous. This is not a monster crotch rocket, this is just a little scooter.

Here's the battery pack that I finished last night. It's going into a metal container that I am building for it. I think I may take your advice and place the BMS on the outside of the "battery tank" rather than the inside. BTW those are not cooling fans on the BMS, they're just imitations added by the maker.

But I would need to extend the ballance wires in that case and that sounds like a hug PITA.

 

[john61ct]

Building up your DIY wiring and connector skillz is a 101-level requirement of the hobby, better to start sooner than later.

 

[atkforever]

I own several daly BMS and I can say they are good. Amp ratings are correct and temp cuttoff works as expected.

I think the problem comes from amazon, mines came with a box and a manual (i've ordered them on Aliexpress though). One BMS has fried after 1 year of strong usage and the seller sent a replacement for free...

Do some researches on youtube, they are many videos of guys reviewing BMS from daly.

 

[mannydantyla]

Building up your DIY wiring and connector skillz is a 101-level requirement of the hobby, better to start sooner than later.

right on though I'm not sure why you said this, there are ring terminals crimped to the ends of the red and black wires, but I thought I would wrap them in tape until their attached to something

 

[mannydantyla]

I own several daly BMS and I can say they are good. Amp ratings are correct and temp cuttoff works as expected.

I think the problem comes from amazon, mines came with a box and a manual (i've ordered them on Aliexpress though). One BMS has fried after 1 year of strong usage and the seller sent a replacement for free...

Do some researches on youtube, they are many videos of guys reviewing BMS from daly.

good to hear! Thanks!