Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Can you use a 10s BMS as a 9s BMS
#1
I am converting a 36v drill to 18650

The problem I had was that my battery was producing around 42v and something in the connector area inside drill started smoking!

I considered a step down device from 42v to 36v but the appropriate size would not fit is the space I have available.

So I took out two cells thus giving me 4.2v x 9 = 37.8v, I tested the drill and smoke issue resolved.

[Image: ibdVhAu.jpg]

However, this raises some questions...

Q1. how do I now wire my 10s BMS when I only have 9s now?  Clearly it was expecting the following voltages

If I discard Wire 1 then wire 2 will not be happy with 4.2v as it was expecting 8.4.

But I can't disgard Wire 10 because it is wired internally in the BMS to the Main terminal B+

Q2. So do I just connect wire10 and wire9 to the last positive cell, that way the circuit in the BMS for wire 9 which would be expecting 33.3 to 37.8 would be happy and the circuit for wire 9 which would be expecting 37 to 42 would be happy, EXCEPT when the voltage on wire 10 falls below 37 which is only 0.8v.

Q3. Will having Wire 9 & 10 on the same contact cause any problem?

Q4. Is BMS only used in charging

Q5. Will it affect operation of the drill?

Q5. Will I still be able to use my 42v 3a charger, it does have a 36v on there but the rest is Chinese

I have uploaded image incase anyone can read Chinese!

[Image: SCQ8eQ7.jpg]

It was ordered from ebay

https://www.ebay.co.uk/itm/383114371013
Reply
#2
Most bms devices are not meant to run other than advertised. It takes a little extra circuitry to make it a lower series connection.

However, you "could" try to and see if shorting pins 9 and 10 together if that'd work. So you'd have 2 wires going to cell 9 instead of just 1. But, not all bms' are designed this way. The TI BQ769x0 series ICs require shorting wires in the middle of the series. So on the 7s making it a 6s, you'd short wires 3 and 4, for example. you'd need to look up the datasheet for the IC of your bms
18650 likes this post
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
(this chat is not directly affiliated with SecondLifeStorage; VALID email req'd)
Reply
#3
If you want to read chinese you can use the google translate app with the camera. It will read and translate it live and show you what is on the plate.
Reply
#4
(03-26-2020, 06:31 PM)gpn Wrote: If you want to read chinese you can use the google translate app with the camera. It will read and translate it live and show you what is on the plate.

Thanks but I do not have the tech to make that work, perhaps you could do it for me and post the translation here



Thanks for your reply, I do not think there are 9s versions, I guess I have nothing to lose if it cooks it other than the cost itself.

I opened up the drill to see what was causing the smoking, I could not really determine a cause.  It seemed to be coming from where the battery packs connects to the drill but there was nothing much there. just wiring and a heatsink.  Then it went to the drill motor.

I wonder if it is that the battery which were 2 ryobi 5s2p's in series so 10 amps being too much for the wiring.

Hard to determine the amps of old 1.2v nicd cells


If anyone else can answer

Q4. Is BMS only used in charging

Q5. Will it affect operation of the drill?

Q5. Will I still be able to use my 42v 3a charger, it does have a 36v on there but the rest is Chinese
Reply
#5
(03-26-2020, 08:16 PM)18650 Wrote:
(03-26-2020, 06:31 PM)gpn Wrote: If you want to read chinese you can use the google translate app with the camera. It will read and translate it live and show you what is on the plate.
Thanks but I do not have the tech to make that work, perhaps you could do it for me and post the translation here

Do you not have an Android phone/tablet accessible?? I think it's even available for iOS as well.

(03-26-2020, 08:16 PM)18650 Wrote: If anyone else can answer

Q4. Is BMS only used in charging

Q5. Will it affect operation of the drill?

Q5. Will I still be able to use my 42v 3a charger, it does have a 36v on there but the rest is Chinese

The BMS is between the charge/discharge. It controls over charging and over discharging. Otherwise, the BMS wouldn't be doing it job very well.

The BMS doesn't "directly" effect the drill except in the over-discharge or over-current draw. Tho, with most tools, you would be hard pressed to do over-current draw.

For a fully charged 18650, 4.2 * 9 = 37.8V. 42V is waaaay to high. This would take the cells to 4.6V if the BMS doesn't turn off. Also, LiIon cells really need to have a proper CC/CV charge curve to achieve fully charged status.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
(this chat is not directly affiliated with SecondLifeStorage; VALID email req'd)
Reply
#6
(03-27-2020, 01:28 AM)Korishan Wrote: The BMS is between the charge/discharge. It controls over charging and over discharging. Otherwise, the BMS wouldn't be doing it job very well.

The BMS doesn't "directly" effect the drill except in the over-discharge or over-current draw. Tho, with most tools, you would be hard pressed to do over-current draw.

For a fully charged 18650, 4.2 * 9 = 37.8V.  42V is waaaay to high. This would take the cells to 4.6V if the BMS doesn't turn off. Also, LiIon cells really need to have a proper CC/CV charge curve to achieve fully charged status.

Thanks for your reply and for clarifying the function of the BMS.

So I guess I will have to go buy a 36v charger

Does anything on the ebay listing suggest it may vary, I am still wondering what that 36v is on the box.

Unfortunately I only have work phone and it is locked down to prevent me installing apps.

If anyone can translate what it says I would be grateful, I did try Google Translate online but it does not seem to offer the same functionality mentioned above.
Reply
#7
(03-27-2020, 01:28 AM)Korishan Wrote: For a fully charged 18650, 4.2 * 9 = 37.8V.  42V is waaaay to high. This would take the cells to 4.6V if the BMS doesn't turn off. Also, LiIon cells really need to have a proper CC/CV charge curve to achieve fully charged status.


If I buy a 36v charger I imagine I am losing something, 42v is waaaay to high, so how much could it take, 38v, 39v, 40v (If I can find one).
Reply
#8
(03-28-2020, 11:08 AM)18650 Wrote:
(03-27-2020, 01:28 AM)Korishan Wrote: For a fully charged 18650, 4.2 * 9 = 37.8V.  42V is waaaay to high. This would take the cells to 4.6V if the BMS doesn't turn off. Also, LiIon cells really need to have a proper CC/CV charge curve to achieve fully charged status.


If I buy a 36v charger I imagine I am losing something, 42v is waaaay to high, so how much could it take, 38v, 39v, 40v (If I can find one).


IIRC, the voltage that the charger says is the nominal voltage of the batteries it is designed for. If I understood correctly, you have a 9s battery and that would be, like Korishan said, 37'8V when fully charged or 33'3 nominal. Bit of an oddball config, I think.

I dunno if this would be recommended, but if you don't find a specific charger for what you have, you could use an adjustable boost converter (with a current limiting feature) and charge from a 12v supply.
Reply
#9
(04-08-2020, 07:35 PM)JustACommonHorse Wrote: IIRC, the voltage that the charger says is the nominal voltage of the batteries it is designed for. If I understood correctly, you have a 9s battery and that would be, like Korishan said, 37'8V when fully charged or 33'3 nominal. Bit of an oddball config, I think.

I dunno if this would be recommended, but if you don't find a specific charger for what you have, you could use an adjustable boost converter (with a current limiting feature) and charge from a 12v supply.

If you read the first post you would see why the "oddball config"

"The problem I had was that my battery was producing around 42v and something in the connector area inside drill started smoking!"

To get a boost or buck converter I would need a high amp one, so cheaper to just buy a 36v one, again covered in the thread.

Also covered in the thread is a voltage table where I show the nominal voltages.

So basically you do not bother to read a post, but make a post saying you "do not know if it would be recommended, but"

Can't see why you bother to even reply.

The idea is for someone with some knowledge and authority who might have done before to give credible advice.
Reply


Forum Jump:


Users browsing this thread: 1 Guest(s)