yes i can monitor the voltage thats what i aim to do ,without the bms conected, in the hope that it does not drop below 33v and thus pointing to the bms cutting the power which would be a lot cheaper to repair/replace.
charging new lifepo4
- Thread starter theskip1
- Start date
i found the listing (not the actual listing but the same type and seller ) for my battery.it does not say but it is a v power battery
36V 20AH LiFePO4 Battery Set
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UPDATE
you are quite right it is indeed the battery. put it under test and found it lost volts at an alarming rate, it was soon down below 35v and dropping to below 32v when opening the throttle. this means buying a new cell. i am not going to send it back to china as it will probably cost almost as much as repairing the battery with no garantees of return. so will have to save what i can from my pension, read up on replacing a bad cell, and place myself in the hands of providence.
thanks for all the advice. tony
Replacing lithiun cells is not normally done as it's very important that the correct cell is used, these constantly changing with development. It would be best to try and get a cell from the supplier of your battery to ensure compatibility and minimise risks of accidents.
.
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ok if i can i will. if for reasons that you state i cannot repair it can the battery run ok without the cell by reducing the amph from 20 to say 15 ? thats if it is only one bad cell which i have yet to find out and of course working out the configaration.
just found this over on "endless sphere" wish i had seen it it before buying "vpower" Endless-sphere.com • View topic - ebay LiFePO4 sellers to avoid: ep-battery, volgood
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is there anything positive you can say or is it all doom. (throw me a bone )
i had heard so many positive things about lifepo4 " its the way to go " etc, it all seems to have gone a bit sour. i wish i'd stuck with sla's not so expensive when it all goes t**s up.
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Sorry, I sympathise, but lithium can be a bit inflexible compared with older technologies like SLA, NiCad and NiMh.
I treat LiFePO4 with some reservation since it is so new and e-bike manufacturers who have been trialling it for up to 4 years are mostly still not satisfied that it's ready to replace Li-polymer compound cathode types.
The only ones that seem to have been performing mostly well to date have been supplied by Li Ping who appears to take care with his individual assembly of them and doesn't make extravagant claims.
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I treat LiFePO4 with some reservation since it is so new and e-bike manufacturers who have been trialling it for up to 4 years are mostly still not satisfied that it's ready to replace Li-polymer compound cathode types.
The only ones that seem to have been performing mostly well to date have been supplied by Li Ping who appears to take care with his individual assembly of them and doesn't make extravagant claims.
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ok have now put the battery under a no load test using my old powabyke on full throttle and after a 21/2 to 3 hour wait
it cut out at 36.1v.
i thought this a rather high cut off voltage so contacted Vpower, they said this was normal as their batteries were set to cut at 35-36v ?.
this kind of contradicts what i have heard up to now .are they pulling my leg or is that right ?
after stripping it i found 12rows of 18cells 3 of which were reading .5v lower than the rest (thats 54 cells! ). having been in touch with Vpower previously when they had kindly offered to supply any cells that i might need at the cost of postage only. i somehow think they may change their mind when they find out how many there are !.
any way that's the state of play at the moment . comments and advice always welcome.
tony.
it cut out at 36.1v.
i thought this a rather high cut off voltage so contacted Vpower, they said this was normal as their batteries were set to cut at 35-36v ?.
this kind of contradicts what i have heard up to now .are they pulling my leg or is that right ?
after stripping it i found 12rows of 18cells 3 of which were reading .5v lower than the rest (thats 54 cells! ). having been in touch with Vpower previously when they had kindly offered to supply any cells that i might need at the cost of postage only. i somehow think they may change their mind when they find out how many there are !.
any way that's the state of play at the moment . comments and advice always welcome.
tony.
Attachments
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Each 18 cells group is the paralleled cells giving the capacity, the 12 cells series giving the working voltage.
Since the LiFePO4 cell working voltage range is 3-0 to 3.3 volts, 12 x 3.0 minimum series working voltage is 36 volts, meaning they are correct with the 36 volts cutoff.
From an online data sheet:
Specifications
Since the LiFePO4 cell working voltage range is 3-0 to 3.3 volts, 12 x 3.0 minimum series working voltage is 36 volts, meaning they are correct with the 36 volts cutoff.
From an online data sheet:
Specifications
- Cell voltage: min. discharge voltage = 2.8 V. Working voltage = 3.0 V – 3.3 V. Max. charge voltage = 3.6 V.
I've found a similar problem with a lithium-ion pack I've just contructed.
I've used 3000ma cells, 10 banks of 8 cells in parallel giving a 24ah capacity.
One bank is dropping to cut off voltage long before the rest.
There may only be 1 bad cell in that bank of 8 so I now need to rip it all apart to find the faulty cell/cell's.
how are you conecting the cells up ? do you have the proper spot welder or are you soldering them ? does anybody know a reliable method ?
I'm soldering them which isn't ideal because of heat. I'm using a heavy duty 100watt iron to make the solder process as quick as possible, the heat is only applied momentarily, I also use a large heat sink to track heat away where possible.
The cells I'm using were tabbed but the spot welds were so poor I pulled most of the tabs off with my fingers. I'm not a fan of pin point spot welds and believe soldering gives a much better joint.
I thouhg about trying one of these in my RC days.
Force 4 Cold Soldering Iron - Only £14.95 - Force 4 Chandlery
Not sure how good the joints would be.
Force 4 Cold Soldering Iron - Only £14.95 - Force 4 Chandlery
Not sure how good the joints would be.
I've got one and although they're okay for light duty stuff they are awkward to use. They have a forked tip that depends on the wire your soldering shorting out the tip to produce heat. Absolutely useless for this application.
Glad I never purchased one in the past then.
Solder and good battery bars are better than spot welds and tin (like you said earlier)
Less resistance means better performance and less heat generation when discharging.
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