Help with battery replacement

Electrically assisted bikes, trikes, etc.
Davewm5
Posts: 2
Joined: 10 Oct 2017, 5:26pm

Electric bike battery

Postby Davewm5 » 10 Oct 2017, 5:46pm

Hi I'm a newbie to this site.

I used to do quite a bit of cycling but after a knee operation followed by an operation on my spine I was not able to do this very well anymore.

I tried an electric bike that a friend had and found I was able to manage really well. This bike had been bought new a couple of years before but due to ill health my friend was unable to ride it.

I've bought the bike and have been reasonably pleased with it, however I'm now having some battery problems.

The battery is a 36 volt 16 amp liFe PO 4. After charging this until the green light comes on I checked the output voltage and it's only reading 21.9 volts.

Thanks for sticking with me this far. Does this mean the battery will need to be replaced soon. I've a suspicion that the battery was not being kept charged whilst the bike was not being used.

Any thoughts/comments would be gratefully received.

Kind regards

David

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mjr
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Location: Norfolk or Somerset, mostly
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Re: Electric bike battery

Postby mjr » 11 Oct 2017, 12:31pm

Davewm5 wrote:The battery is a 36 volt 16 amp liFe PO 4. After charging this until the green light comes on I checked the output voltage and it's only reading 21.9 volts.

What's the bike and what's the green light meant to signify? Ready to use or fully charged? Is there any range/power-remaining display on the bike?

If the green light means fully charged, it does sound like the battery is very degraded and may not be useful much longer, but someone more experienced with e-bike batteries may think different.
MJR, mostly pedalling 3-speed roadsters. KL+West Norfolk BUG incl social easy rides http://www.klwnbug.co.uk
All the above is CC-By-SA and no other implied copyright license to Cycle magazine.

Davewm5
Posts: 2
Joined: 10 Oct 2017, 5:26pm

Re: Electric bike battery

Postby Davewm5 » 11 Oct 2017, 10:31pm

Thanks for your reply, MJR.

The green light signifies that the battery is fully charged. There's no range read out on the display.

I'm inclined to agree with you that the battery may be on the way out.

Thanks once again for your answer.

jk49
Posts: 100
Joined: 6 Apr 2013, 7:51pm

Re: Electric bike battery

Postby jk49 » 13 Oct 2017, 2:32pm

Maybe try the pedelecs forum. There are some very knowledgeable (about ebike stuff) contributors over there.

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georgew
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Joined: 27 Jan 2007, 4:23pm

Re: Electric bike battery

Postby georgew » 14 Oct 2017, 2:15pm

jk49 wrote:Maybe try the pedelecs forum. There are some very knowledgeable (about ebike stuff) contributors over there.


+1

There are some very knowledgeable people on that forum and they are very helpful with problems such as the OP poses.

hemo
Posts: 48
Joined: 16 Nov 2017, 5:40pm
Location: West Sussex

Re: Electric bike battery

Postby hemo » 16 Nov 2017, 10:18pm

A month or so old now the only way to know what is really happening with the battery is to check it with a digital volt meter ( dvm) , opening up the battery and taking readings from the Battery management system (bms) sense wires is required. Also a preliminary check of the charger is needed to rule it out of the equation by simply measuring the chargers battery connector to confirm the voltage reading is correct for lifepo4 should be about 43.8v.

Most lithium chemistry has a 3.6v nominal rating so 36 = 10 cells in series or 10s, usable range 3.4v - 4.2v for ebike
Lifepo4 has a nominal voltage of 3.3 so 36 = 12 cells in series or 12s, usable range 2.8 - 3.65v.

21.9v is poor and indicates a knackered battery usually a cell group or two is failing or it could be a simple fault like an internal charge wire has come loose so leaving a cell group low. the only way to really know what's up is to open it up and check as said with a dvm.

Ianmangham
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Joined: 13 Dec 2017, 6:12pm
Location: Doncaster south Yorkshire

Help with battery replacement

Postby Ianmangham » 13 Dec 2017, 6:31pm

Hello anyone, I have a Chinese unrestricted kit 250w front geared hub with 36v 10-15amp controller, came with a 36v "42v cgarged" 8ah battery, anyway the battery is dead after 4 year's of use, I want to know if I can wire 2x6s 30c rating 22v 6000mah rc loop battery's in series, will it run ? If I take it easy because I'm 15amp over the controller limit

hemo
Posts: 48
Joined: 16 Nov 2017, 5:40pm
Location: West Sussex

Re: Help with battery replacement

Postby hemo » 14 Dec 2017, 4:51pm

Ianmangham wrote:Hello anyone, I have a Chinese unrestricted kit 250w front geared hub with 36v 10-15amp controller, came with a 36v "42v cgarged" 8ah battery, anyway the battery is dead after 4 year's of use, I want to know if I can wire 2x6s 30c rating 22v 6000mah rc loop battery's in series, will it run ? If I take it easy because I'm 15amp over the controller limit


Yes you can 12s battery will give you up to 25% more speed and torque. Most 36v controllers ( if it has a main inrush capacitor of 63v) will take the extra voltage in your case 50.4v max, though with lipo's you don't get much extra range or use from going 4.2v per cells so better just to balance out at 4.1v, use lipo alarms and make sure you don't go below 3.6v per cell otherwise they will crash quickly and become very unbalanced.
You don't have to worry about amps draw as the controller will do that, it will only draw amps it can provide. It is better to have a battery with greater amp rated cells then one with less amp rated, cells will be less stressed and give longer life. The most damage you can do is fry the controller, replacement controllers can be had for about 20/25 quid.
You can easily check for the capacitor, if the controller is an oblong ali box one just undo the 4 small screw on the opp end to the wiring and you should see the main inrush cap adj to the U shaped shunt which restricts the amps. You can also modify the shunt to accept more amps draw by shouldering one leg by adding some solder, max amount of solder should not exceed 25/30 % of the total shunt length.
Last edited by hemo on 14 Dec 2017, 5:13pm, edited 1 time in total.

hemo
Posts: 48
Joined: 16 Nov 2017, 5:40pm
Location: West Sussex

Re: Help with battery replacement

Postby hemo » 14 Dec 2017, 5:11pm

I run multiple lipo batteries of various capacities on my bikes you can connect either in Parallel or Series.
When In parallel they need to be quite close in voltage as the amp rush to equalise can be very high and the wiring can get very hot.

Ianmangham
Posts: 4
Joined: 13 Dec 2017, 6:12pm
Location: Doncaster south Yorkshire

Re: Help with battery replacement

Postby Ianmangham » 14 Dec 2017, 10:47pm

Hello,thanks mate,I've had the esc open and it has 50v caps, I'll get lipo voltage alarms for the Flourion 22v 6s 6200mah battery's, they're only £42 for 2 on ebay UK "cheap as chips I thought" only thing is I've only the standard brick charger that came with the kit,so ill have to buy a balance charger ?

Ianmangham
Posts: 4
Joined: 13 Dec 2017, 6:12pm
Location: Doncaster south Yorkshire

Re: Help with battery replacement

Postby Ianmangham » 14 Dec 2017, 10:52pm

Yes I've played with the shunt before,I'd wrap wire around it,I've never used one of those fancy lipo balance chargers before only the standard box type you'd get with rc car's, I can't seem to find one that runs off 240v ,do I have to buy a car battery charger to run one of those lipo balance chargers?

Ianmangham
Posts: 4
Joined: 13 Dec 2017, 6:12pm
Location: Doncaster south Yorkshire

Re: Help with battery replacement

Postby Ianmangham » 14 Dec 2017, 11:57pm

Found one that runs offrom the mains on ebay lolz

hemo
Posts: 48
Joined: 16 Nov 2017, 5:40pm
Location: West Sussex

Re: Help with battery replacement

Postby hemo » 15 Dec 2017, 9:41am

Lipo's are a faff and a bit of a pain in the ar*e if you use multiple's to form an ebike battery. With 50v cap's then 4.1v is the max charge for lipo and then the cap may pop if it sees a spike at all, though if this is the case new controllers (esc in rc talk) are not expensive to replace and then you can get ones with 63v caps.
Lipo's have no BMS for cell/battery charge/discharge management unlike 18650 batteries so you have to act as the BMS and monitor both charge and discharge on an e bike, with RC if it crashes and burns you get away with it a bit different when your sitting on them .

Charging wise I use a 240v PSU wired to a lipo balance charger, DC lipo balance chargers are better then AC one's as you can get more watts for charging. With lipo's you need to be near by and keep an eye on them when charging, when not in use use storage charge of 37 - 38.5v and charge prior to use.
With 6200mah you might only see 10- 12 miles range with lipo.