very baffaling battery question

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csjones10d

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Jan 5, 2015
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hi
I need some help with this very baffaling battery question, I will start of by telling you I wanted to boost my battery power by adding another battery to my lifepo4 48v 20ah
so I bought a 24v 20ah lithium battery to give me 72v 20ah of power I was using this combo with a 72v 60ah controller. when I first tried to get it to work I could not till I took off the bms on the lithium battery and for some reason it all then worked ok.

now I have just charged both batterys and both are fully charged both checked with a meter this is where it get bafflaing now when I connect it to my controller even though when iv checked the power coming from the batterys wired together and I am getting 75v when I connect to the controller the reading on my computer is saying I just have 36 volt so I thought it could be iv done something to the controller so iv run my 48volt battery with 2 old 12 volt batterys that I know work together to again give me 72 volt and my computer is reading the 72 volts again and the bike is running ok co conclution is it is a problem with the lithium battery but I don't know what as like I say its reading 23volts with a meter so it should work ok.

please help if you can I am realy stuck and have a battery that I cant use I have now connected just my 48 volt lifepo with a 48 volt controller that I have and all is ok so at least I can use my bike till iv got to the bottem of this broblem.

thanks chris
 
Please post pictures of the setup including how you wired it.
What battery/bms?

This is a typo, right?

...its reading 23volts...
Click to expand...
 
One or both bms's could be shutting off. But with this little info, it's a pure guess.
 
yes ecycler it is a typo iv got 54 volt at the moment on a full charge from my 48v battery also I will wire it all up again later in the week and take some pics for you to show what I have done when iv got both battery wired up
 
If it's a typo, you could help us help you by telling us what it was *supposed* to be.

Also, most people trying to help you could do it better if you didn't have a bunch of separate threads about your stuff but instead kept it all in a single project thread, so they'd have all the info you've posted so far right there, at least. ;)
 
also when I connect the 2 batteries to the controller I don't get a spark when I connect just the lifepo 4 only I do get a spark
 
One of the many possibilities, is the first power up of your new controller fried something defective inside.

No spark when it connects, makes me suspect a bad capacitor.

No offense, but you didn't hook it up reverse polarity at some point?
 
Since he does get a spark with just one battery but not with both in series, it's probably not the controller, directly.



My guess is something is wrong with the second battery; perhaps it's BMS has detected a problem with a cell and shut it off.

Or, the BMS of the first battery has shut off whenever it's connected in series with the other one (would make more sense for the voltage reading).
 
I have taken the bms of the faulty battery and it still wont work so it cant be the bms its got to be faulty in some way but I still don't understand how it can give out a reading using my multimeter but put out no power
 
I might not have been clear, but if it's a BMS thing at all, then it's probably the BMS of the first (original) battery, to get the voltage reading you do. Did you bypass that one, too?
 
Dear amberwolf

I will try to explain from the start what I have done when connecting this new battery please be patient as I don't know to much about batteries.

what I wanted to do is increase the power of my bike so I bought a second battery it is a lithium 24 v 20 ah battery I used this second battery in series
with my first batter that is a 48 v 20ah lifepo4 battery.
when I first connected them together I could not get no power from the 2 batteries joined in series using my multimeter so I removed the bms from the new
battery ie 24v 20ah lithium and for some reason this worked and was ok and ran my bike giving me over 72 volts total power.

the trouble started when I charged both batterys when they wanted charging, I put them back in series after charging and connected them again to my controller
just as before but this time they would not run my bike and the power reading on my computer showed a lower power output than before see photo also to confuse me
more when I tested the two batteries together I expected no volts or a lower reading to come from the two batteries as they now did not work with my controller but I still
got a reading of 72+ volts :? at this point I thought my controller was at fault but I checked this out by connecting my first battery the lifepo4 with a 24 v 6ah battery that I have and again everything worked the controller was ok and it ran my motor so it could not be my controller that's what I think at this time.

so all this leaves me were I am now just running my first battery my lifepo4 batter and a smaller controller that I use with this batter and all is ok again
but I have a lithium 24v 20ah batter that I cant use don't know if its broken and confused that its still giving me a multimeter reading of 24v

can I strip it down and check each cell some how and if some are ok I would buy some more cells to go with them and build a 72 volt battery my self and with a bms run this battery alone on my bike.

hope this makes some sense as I said my knowledge of battery workings is very limited any info you can give me or if someone else out there knows
what could be the trouble please point me in the right direction as this is all doing my head in.

thanks chris
 
don't take my volt reading as fact iv just wrote down a value close to what I can remember what the readings where all I can say is when my 48 v lifepo4 is fully charged it goes to about 53 volts as for the 24v lithieum that was giving me 24v spot on what it should be both batteries where charged to a cut off point decided by the battery so a closer reading if you want one would be a total voltage of 53 ish + 24 total 77 volt ish if you know what I mean.
 
forgot to mention its six cells not 7 I took 1 cell off so not to go over the 80 volts as my controller is a 72 volt controller and I thought rightly or wrongly it could damage the controller.
 
more tech info if it helps

the lifepo4 battery is made up of 123 cells at 20 ah each still has bms attached
the lithium was 7 rows of 7 now its 6 rows of 7 and total ah I was tolled was 20 ah bms removed
 
My best guess at this point is that you are hitting the HVC of your controller when both of the batteries are fully charged. It just happens to be a the perfect voltage. The 6ah battery you subbed in likely has just a slightly lower nominal voltage. When you got that first ride in when they both worked together were the batteries hot off the charger or had they sat for a little while?

1. Try bypassing the BMS on both batteries and if it is still messing up, then you will know it is the controller HVC and not the BMS of the 18650 pack.
2. Discharge both packs to 50% and then try hooking them up to the controller to see if it functions. This could rule out that the BMS on each pack is fine and it was definitely the HVC.

Otherwise, there is something pretty wrong with that 24v 18650 pack it should still power the bike for a while. Have you checked all of the voltages at the sensor wires to make sure it is balanced and nothing is terribly wrong with it?
 
thanks for your replies I will try some of the things you have suggested and get back with the results fingers crossed I can get to the bottem of this issue
 
csjones10d said:
don't take my volt reading as fact iv just wrote down a value close to what I can remember what the readings where
Click to expand...
If you can't give us actual readings, we can't give you accurate help--we're just guessing, and it's just a waste of everyone's time.

I strongly suggest that you get a notebook, and write down every step you do for every test, and every measurement as you make them, and why you are making that measurement.

Part of that will help us help you by getting us accurate information.

Part of that will help you by you then knowing what you already did and what you still need to do.




Next, you really need to check what the voltage reading on the output of *each pack* is, when you have them in series and connected to the controller. And you need to write them down as you do the measurements, so you can post the actual readings.

That will tell you which pack the problem is with.






csjones10d said:
the lifepo4 battery is made up of 123 cells at 20 ah each still has bms attached
Click to expand...
123 (one hundred and twenty three) cells, if they're each 20Ah, does not make a 48V 20Ah battery, because to get only 20Ah that way you'd have to put them all in series.

Since LiFePO4 is about 3.2V per cell nominal, that's almost a 400v (four hundred volt) battery.

I think you need to re-count the cells.


Almost certainly the problem is not with the newer smaller pack, but:

the lithium was 7 rows of 7 now its 6 rows of 7 and total ah I was tolled was 20 ah bms removed
Click to expand...
That would be 2.86Ah per cell (20 / 7). Not impossible, but that's fairly high for 18650 type cells, if tha'ts what they are.


When you removed one row of cells, exactly what did you do to disconnect and reconnect things to restore the series connections?
 
HI

I have striped down the lithium battery down to individual cells as the battery was no good as it was so I could see exactly
what the problem was, and now its striped it is clear to see what was wrong,

bellow is a list of readings from the cells and I could do with some advice as to which cells are ok which cells I can salvage and which are
dead also how can I charge each cell on its own if they can be salvaged can you recommend a charger.

what I am thinking of doing is when iv got all the cells in a good way I could get some more and build a battery from this sort of cell and just use this battery
on its own.
bellow are the reading from the cells

number of cells reading
3 4.2
5 4.1
1 4.0
7 3.9
2 3.7
4 3.5
1 3.4
2 3.3
1 3.1
1 2.8
1 2.6
1 2.1
2 1.4
1 1.2
1 1.1
1 0.9
2 0.8
3 0.6
1 0.3
5 0.1
2 0.0

hope this make all the last posts make sense as I think what I did was when I removed the bms and charged it for the first time because it had no bms on it
the charger just killed the battery.
 
start by throwing away all the batteries below 2.8
 
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