Adding a bms to lipo 10s.

[Nealh]

As AWOL asked about lipo bms I used, I thought I would do a how to though it has been said and done before on here.

20a continuous output bms I used with switch wiring and balance function.
Barring the switch bms is much the same as the 15a version so should handle a 50 - 60a peak/spike output.

https://www.aliexpress.com/store/product/36V-li-ion-battery-BMS-36V-20A-lithium-ion-batteries-BMS-With-balanced-function-and-ON/623665_32830759079.html?spm=2114.12010612.8148356.20.21857abeDNtiCE

Before 6+4s lipo.


After.
Sense wire jst and wires purposely left exposed in case of need to check cells with dvm.


1. Hot melt two cell packs together and measure both voltages.
2. Place bms and hot glue in position.
3. Cut and solder/insulate sense wires one at a time (leave bms sense jst unconnected ), determine cell #1 b- (0v) with dvm should be first black thin wire on pack where thick black comes from , next is #2 (3.7v), #3 (7.4v) until you reach the first thin red. Final thin red on pack should be b10+.

4. When you get to first thin red it has to be connected to the first thin black wire of the next jst (which will be 0v) these two soldered together is the next sense wire connection, once done you should have equal amount of thin sense wires left to connect.​

5. Make series connection. Cut inner /middle thick black wire and inner/middle thick red, bare,solder and insulate joint. dvm probes on two remaining thick wires should add up to measurement in #1
6. Make discharge connection. Cut P- discharge wire from bms to length and solder/insulate to wire connector with short thick black and long red still connected.
7. Cut other thick long black (B-) still in connector and solder/ insulate wire end to BMS B- wire.
8. For charge lead you will carefully need to cut all way a long top of cell pack with thick long red wire and solder your red lead to top or side of the thick red soldered one. Once done cover with Kapton tape and reseal. Solder other end to charge connector + and solder in C- bms wire. I used the green /black simple connector off ebay which is marked + & -. If using a solder type connector central inner end is +, you will need to do a continuation check to find correct + solder pin.
9. For 2 pin switch just connect one on each doesn't matter which way as both are v+.
10. Fit sense jst to bms turn on switch and measure voltage should be same value as you measured in #1 & #4.
11. Connect charger switch battery on and check voltage input.
12. If all is good heat shrink wrap together and then hot glue charge connector and switch to top.
13, Fuse not used as I use inline fuse on bike discharge v- wiring.

 

[anotherkiwi]

Can you charge at 10 Amps (1C)?

The other advantage for me of having vanilla LiPo bricks is charging off grid from a 12v battery. This is the view from the 12v battery in question, the solar panel is just to the right...

 

[Nealh]

Carefully cutting and keeping wires as short as poss allows for a neater finish, though bms needs gluing in place first. I place mine as near to the top as poss to still give the jst a bit of protection but leave a bit of a cut out of the shrink to allow hot air from bms to escape, leaving the sense wires about 20/25mm long I'm just able to get a finger under them allow enough slack to disconnect if needed.
When working it all looks a bit untidy but as soon as you shrink wrap it starts to look much neater.
On top I goop hot glue around the switch and charge plug as well as the thin feed wires to hold them down.

 

[Nealh]

1C with mine would be 8a but other wise no, bms is 5a max capable. I don't need fast charge so happy with 2- 2.3a rate. Full slow charge in approx. 3hrs 40m or 4hrs.

 

[awol]

Thanks for a great write-up, just ordered a couple of those bms's. For some reason I thought you couldn't put Lipo's on a 'normal' BMS but will be giving it a go now. Now need one of those hot glue things from Aldi next time I see them in there.

 

[anotherkiwi]

Thanks for a great write-up, just ordered a couple of those bms's. For some reason I thought you couldn't put Lipo's on a 'normal' BMS but will be giving it a go now. Now need one of those hot glue things from Aldi next time I see them in there.

Cells be cells lad! Many of the older generation Lithium behind the seat post style batteries contain LiPo pouches and a 'normal' BMS. You can take LiPo down to an LVC of 3.3v per cell with no risk other than shorter battery life.

What I like about raw LiPo is the charge times at 1C - under an hour for my 10000 mAh bricks be it Multistar or Graphene (more like 48 minutes). Since I've started commuting again that is greatly appreciated, I can charge during breakfast! I am not taking them much below 37.5v at the moment so the whole 20 Ah battery can be done in just over an hour and a bit. Pretty steep around here so I am seeing 0.9v sag instead of the more usual 0.6v tops.

 

[Nealh]

My new batch of dc charge connetors have arrived so I can convert my other pair of bricks, so will try and remember to include some pics to go with the write up and match the number order of how to.

 

[awol]

determine cell #1 b- (0v) with dvm should be first black thin wire on pack where thick black comes from

Nealh, You've just answered the problem I had when wiring my packs together for my Speedict. I did not kow the packs had to be put in series only one way round and blew a couple of plugs to bits until I realized, however I still did not know why that was the case, but now you've answered that.

 

[Nealh]

#1 & #2.
4S & 6S hot glued together with bms in place ( hot glued as well).
Notice all bms wire ends insulated to prevent mistaken shorting.


#3.
Soldering sense wires using a helping hand, snip jst wires to required length at the same time. Cut only one battery sense wire at a time.


#4.
Soldering the red sense wire (15.2v) of 4s pack to b-/0v wire of 6s pack.

Same pair now soldered to jst lead and shrunk.

All 10 sense wires soldered giving pack reading 10 x 3.84v.


#5.
Making the series connection as with all the other connections don't forget to slide a bot of heat shrink on first to cover joint after.

Series connection made and pack voltage reading.


#9.
Switch soldered on, two red wires have no solder order so just do them.

 

[Nealh]

Only 4 more wires to connect maybe tomorrow or next week.
I will add pics again.

Yellow BMS charge wire goes to dc charge plug negative/v-, the red supply wire prroces as described in post 1/#8 needs soldering on.

Black BMS wire B- needs connecting to the uncut thick black also B-/pack -wire still connected to the XT60, both will need cutting to required length. ​

Blue BMS wire is the discharge wire so needs to be soldered to the already cut thick black wire (XT60) which also has the thick red connected.

Once all this is done ensure the switch is off and connect the bms jst lead, to finish plug charger in and check charging is occurring (not forgetting to turn on battery switch).

 

[Nealh]

#6.
BMS discharge/P- soldered to black tail of XT60.

Solder Joint smoothed out and shrunk.


#7.
BMS B- soldered to pack B- and shrunk.

B- hot glued in place.


#8.
Pack V+ exposed to solder charge plug V+ wire on to.

Charge V+ & BMS C- connected to DC plug.
My chargers use 5.5mm x2.1mm
I used jst sense offcut 22awg/7a capable.


#10.
All connections made BMS connected and voltage checks out, switch is on.

Voltage reading, switch is off.


#12.
Pack heat shrunk following charger connect up and working.


Last job will be a bit of black duck tape to strap over the top wires in case of testing is needed.
Job done I now have a pair of 10s 8ah packs.

 

[awol]

Thanks for taking the time to do such a detailed step by step write up.
The end heatshrink under the jst wires, is that just a strip of heatshrink covering the end held in place by the final wrap or goes all the way around the length of the cells?

 

[Nealh]

The shrink under the jst's is a smaller size shrink wrap for my 3s packs so I cut it and it reaches down about half way, a dab of hot melt keeps it in place until place the final wrap. Then it all get's a good wave over of my heat gun.
If you want to you could place the shrink over the jst's but then you would loose the easier option of any manual monitoring of cells if needed to do so for any reason.
These will sit nicely in my additive bike bag that straddles the top on the ht mtb.

 

[awol]

I'm one step nearer, look what arrived. Just need some Kapton tape and blue heatshrink now.

 

[Nealh]

Show us a pic or two during or when finished Awol, maybe you make neater job of it then I did.

 

[awol]

Are either of these the type of switch needed?
https://www.ebay.co.uk/itm/CD7B-10pcs-Mini-On-Off-Latching-Latch-Push-Button-Switch-Locking-Car-12mm-black/263861218240
https://www.ebay.co.uk/itm/10x-1A-30V-DC-250V-Black-Latching-On-Off-Mini-Torch-Push-Button-Switch/302554785168

 

[Nealh]

The first one is the one I used Awol, It doesn't take any real current to speak of as it wired in to the V+ side from the bms.

 

[Nealh]

Took my 8ah 10s lipos out today for a ride as extra range. I use a PF triangle battery and these in a rear rack top bag.
Only used one lipo to 37.4v and got 25 miles range, didn't need the second so it is on a slow discharge.

Used approx. 6ah down to 37.4v so wh usage was about 8.64wh per mile, I know longer have the leg strength I had back in the day so can only dream of the wh AK manages.

 

[anotherkiwi]

Took my 8ah 10s lipos out today for a ride as extra range. I use a PF triangle battery and these in a rear rack top bag.
Only used one lipo to 37.4v and got 25 miles range, didn't need the second so it is on a slow discharge.

Used approx. 6ah down to 37.4v so wh usage was about 8.64wh per mile, I know longer have the leg strength I had back in the day so can only dream of the wh AK manages.

We didn't grow up on the same farm! The silly thing is around here the slopes have suddenly become the same kind of % gradient that I knew in my youth. That wasn't supposed to be in the plan!

 

[awol]

Another step nearer, got some switches and heatshrink. Did not know what size heat shrink to buy so ordered a few differenty sizes.
Turns out the order was just over £15 gpb which apparently means I get charged import VAT on the whole amount plus a Royal Mail admin charge ontop has nearly doubled the price of my heatshrink. An expensive lesson.