Three wire Bms to two, is it possible?

Lazeyboy

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I have to replace the BMS which has 3 wires, C- P- B- similar to the fist picture. The one I would like to fit is a Daly 3S-24S BMS 3S-24S but has only 2 B- P-, 2nd picture, it has a balance feature which I would like to have. The battery is a silverfish style with a key on top that locks the battery to the bike and turns it on and off. Does anyone know if and how it can be done or should I stick to a 3 wire?
Thanks anyway.
 

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saneagle

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It's easy. You wire the charge negative to the P-. For safety, you should add a 5A fuse to the charge positive wire if you don't already have one because the BMS will allow charging up to 25A.
 
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Lazeyboy

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Great! Thanks so much, forgot to mention that in the housing there is a fuse a charger socket and a type of useless 4 stage led for capacity info.
Thanks again.
 

Woosh

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It's easy. You wire the charge negative to the P-. For safety, you should add a 5A fuse to the charge positive wire if you don't already have one because the BMS will allow charging up to 25A.
could a number of fires have been prevented if there were a fuse inline with the charging wire?
 
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Lazeyboy

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Here’s a couple of photos showing the actual non-description bms.
Full disclosure, I was trying to use a 4amp charger from another bike instead of the 2amp that came with it. I had to change the socket from a dc power type to a XLR so cutting of and re soldering them. Both had a blue and brown wires so took it for granted brown to poss and blue would be neg. Idiot. Should have tested.…. Only after crackle-spark sounds did I then discover then one I was trying to replace blue was poss brown was neg. = BMS is now outputing 33v from a 48v battery. Lesson learned.…..Didn’t blow the fuse though.
 

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saneagle

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could a number of fires have been prevented if there were a fuse inline with the charging wire?
Possibly if someone got the idea to use a high power charger. Many BMSs have a separate MOSFET to control the charging, which would blow if you tried to put too much current through it, but those without a separate charge MOSFET would allow at least four times as much current through. In the case of the BMS above, it'll allow 25A before it shuts off. That much charge current would cook many of our typical ebike batteries that are supposed to be charged at 2A. A fuse at least gives some level of protection against people doing stupid things.
 

saneagle

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Just one more thing, (Columbo, fan,) Is there a particular order to connect the wire to a BMS or doesn’t it matter?
In your case, it doesn't matter, but probably best to leave the multi-pin connector 'til last, and always check its pin voltages before connecting to the BMS, as it's easy to get them out of sequence.
 

Nealh

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The only difference between the two BMS types is the charging .
3 wire has seperate charge port , 2 wire one charges and discharges via the same port .
Those DALY's can be a bit suspect and fail , if one does find it fails then use another BMS brand.
I have had a couple fail on me , one failed and completly killed a 13s 6p battery . Left the SOC at 38.5v and I month later found the battery dead.
The other failure was my current 44v drinks bottle battery , BMS wasn't able to switch to allow charging and found less the 20v on the discharge. I caught this one early and desoldered the BMS. Fitted another BMS brand and all has been well.

Also there is thread or two on ES regarding the failures..
 

Lazeyboy

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The only difference between the two BMS types is the charging .
3 wire has seperate charge port , 2 wire one charges and discharges via the same port .
Those DALY's can be a bit suspect and fail , if one does find it fails then use another BMS brand.
I have had a couple fail on me , one failed and completly killed a 13s 6p battery . Left the SOC at 38.5v and I month later found the battery dead.
The other failure was my current 44v drinks bottle battery , BMS wasn't able to switch to allow charging and found less the 20v on the discharge. I caught this one early and desoldered the BMS. Fitted another BMS brand and all has been well.

Also there is thread or two on ES regarding the failures..
Thank for your reply. By what you’ve said the Daly’s sounds that they could be untrustworthy and a bit problematic. Almost sounds like the balancing feature didn’t stop or something. I thought I’d try a more expensive type as the cheaper ones seem to be nondescript, and I do like the balancing feature. Could you suggest another brand as I really don’t want to lose a battery?
 

Nealh

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Curently for my needs I'm using 'Be Much Safer' brand. They have some with balance and some without, I also prefer switched BMS.
 

Sturmey

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could a number of fires have been prevented if there were a fuse inline with the charging wire?
I have seen in a Phylion battery a 'thermal' fuse on the charging circuit standing up under the BMS circuit board thats pushed down between two cells and embedded with white thermal goo. This fuse blows when the cells reach a certain temperature rather than due to excess current as far as I know. There was also two separate thermistors embedded with white paste in the cells.
 

Lazeyboy

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Curently for my needs I'm using 'Be Much Safer' brand. They have some with balance and some without, I also prefer switched BMS.
Thanks I’ve looked at the BeMuchSafer 13S 35A 30A 48V Battery BMS, just to clarify, does the ‘switch’ operate the balance function?


It’s almost £19 but it maybe more reliable?
Thanks again.
 
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Lazeyboy

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Thanks I’ve looked at the BeMuchSafer 13S 35A 30A 48V Battery BMS, just to clarify, does the ‘switch’ operate the balance function?

Its almost £16 but it maybe more reliable?
Thanks again.
I’ve also seen this that is 2 wire ‘common port’.


Sorry about needing to ask, but is it better to use a 3 wire version? I’m not understanding the need of a 3 wire if, as suggested I can ‘wire the charge negative to the P’?
 

saneagle

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I’ve also seen this that is 2 wire ‘common port’.


Sorry about needing to ask, but is it better to use a 3 wire version? I’m not understanding the need of a 3 wire if, as suggested I can ‘wire the charge negative to the P’?
You need to read the details in the specification:
Balancing function: without.
 

Lazeyboy

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You need to read the details in the specification:
Balancing function: without.
Sorry I thought maybe ‘with switch’ (third one along,) was for turning balance function on or off.
So maybe this one?

2nd one ‘Color: 13S35A with SW’. Ignorance showing, what will the switch do?
 

saneagle

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Sorry I thought maybe ‘with switch’ (third one along,) was for turning balance function on or off.
So maybe this one?

2nd one ‘Color: 13S35A with SW’. Ignorance showing, what will the switch do?
The switch switches the battery output on and off using the output MOSFETs. It's very difficult to get an acceptable solution with an external switch, so it's a very desirable feature, though there are other ways to add a switch to a BMS that doesn't have the pads for one.
 

Nealh

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I’ve also seen this that is 2 wire ‘common port’.


Sorry about needing to ask, but is it better to use a 3 wire version? I’m not understanding the need of a 3 wire if, as suggested I can ‘wire the charge negative to the P’?
Two wire BMS will charge/ discharge thru the same port so utilising the same switching components this can allow for greater current charge though in most cases will be detrimental to battery life.
Three wire charge /discharge via seperate ports so will utilise seperate switching components.
Typically these limit charge current.
 
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Nealh

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As I mentioned someare with balance feature and some without so the full spec needs reading, those without balance still have lvc /hvc BMS control .
As long as one charges fully and not short charging less then full then balance shouldn't be an issue with pucker cells. Over time short charging in the bigger picture of a batteries life isn't going to add much gain in life cycle or usage for an EAPC.
 

Lazeyboy

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As I mentioned someare with balance feature and some without so the full spec needs reading, those without balance still have lvc /hvc BMS control .
As long as one charges fully and not short charging less then full then balance shouldn't be an issue with pucker cells. Over time short charging in the bigger picture of a batteries life isn't going to add much gain in life cycle or usage for an EAPC.
Thanks I think I will go with this one without switch but with balancing.


To tide me over I ordered a daly from Amazon ,


I went to fit it this morning and as I was checking I noticed the polarity for the ribbon connection is reversed so can’t use it. I think the BeMuchSafer shows the correct way round.
Is there a ribbon reversal adapter, and if so what’s the proper name? I have had a search but I only get results for typewriters…..
 

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