Suddenly encountering Low Voltage Cutoff on 18-month-old 24V pack. Advice?

[Coadey]

Hi all,

My 18-month-old Cyclamatic has started acting up again and I'd really appreciate any advice. In short the BMS on the battery seems to be shutting down due to Low Voltage Cutoff before its indicator shows a low charge.

The battery pack is a 24V 10A Li-ion. I'm fairly sure it's an LVC problem because it happens anytime the pack reaches 23.7V under load. I believe it's the BMS because even the onboard charge indicator turns off.

The result is my powered range has been reduced to 4 - 6 miles, and towards that point, forces me to stop and turn the pack off and on again constantly.

Some measurements:

At full charge (which I do after every journey) the pack shows 29.3V when idle, and dips a variable amount under load, at most down to 28.2V or so.

After around 4 miles it reaches 27.9V idle, and struggles intermittently to stay above LVC (wind gust or climb = stop and reset). At over 5 miles it shows 27.2V idle and can only handle a few seconds even on level terrain.

What might cause the pack to hit its LVC while the charge indicator is full bars? Wouldn't the BMS work around any failing/under-performing cell(s)?

Is there anything I can do to prevent it from hitting the LVC so that it might continue providing whatever amperage it's capable of (at say 27.5V?) until it's truly at low charge?

Thanks in advance!

 

[flecc]

I think its probably the battery's cells or a cell at end of life Coadey, it's not unusual for low cost lithium-ion batteries to pack up at 18 months, sometimes even earlier. Even the best often only last about two years. When at end of life they will show all LEDs lit when fully charged, with an off load voltage not much different from when new, but dipping sharply under load and causing cut-out. The switch off/on reset always happens then, but of course is of little use since reapplying the load just causes cut-out again.

 

[Coadey]

Thanks flecc, it's too bad these bargain batteries don't last more than 2 years.

I've been reading a lot about batteries on the forum and I keep seeing mentions of a "Ping" battery. Are they easy enough to use as drop-in replacements, or should I just stick with a Cyclamatic replacement? The later is fully assembled in the proper enclosure for £30 more:

24V 10AH V2.5 LiFePO4 Battery Pack
Cyclamatic Foldaway Battery - The Sports HQ

If the Ping batteries are easy enough to use, could I upgrade from 10AH to 15AH?

24V 15AH V2.5 LiFePO4 Battery Pack

Thanks again!

 

[Fordulike]

Thanks flecc, it's too bad these bargain batteries don't last more than 2 years.

I've been reading a lot about batteries on the forum and I keep seeing mentions of a "Ping" battery. Are they easy enough to use as drop-in replacements, or should I just stick with a Cyclamatic replacement? The later is fully assembled in the proper enclosure for £30 more:

24V 10AH V2.5 LiFePO4 Battery Pack
Cyclamatic Foldaway Battery - The Sports HQ

If the Ping batteries are easy enough to use, could I upgrade from 10AH to 15AH?

24V 15AH V2.5 LiFePO4 Battery Pack

Thanks again!

I would stick with buying another Cyclamatic battery.
Two reasons:

1) Keeps the aestetic look of the bike. Otherwise you'll probably have to stick the Ping on a rear rack, then you'll have a gap where the original battery was. It'll look ghastly.
2) I believe that the overall working voltage of LiFePO4 is slightly lower than the one on the Cyclamatic. Therefore it will feel like it is lacking in power, due to the motor running slightly slower.

Note that I said believe, so I could be completely wrong

By the way, as a stab in the dark, try cleaning the contacts on the battery and on the bike where they slot together.
Use a proper contact spray, not WD40!!
Also bend the contacts on the battery slightly inwards to get a better contact on the bike prongs.
I had this problem many months ago, and had similar symptoms to yours.
Worth a try

 

[Coadey]

Thanks for the tip on the contacts, I'll give that a try! As far as aesthetics, I was actually thinking of putting the Ping battery inside the existing Cyclamatic enclosure. I haven't opened it to see if that's doable though, and I'm mostly curious about the 15AH version to make it worthwhile.

 

[Jocelyn]

Use a proper contact spray, not WD40!!

I've never heard of a 'contact spray' and have been worrying about the state of my terminals/contacts. Where would I find one please?

 

[vhfman]

I've never heard of a 'contact spray' and have been worrying about the state of my terminals/contacts. Where would I find one please?

Jocelyn, something like SERVISOL SWITCH AND CONTACT CLEANER Should do the trick. The link is to Ebay but you can probably get it in other places too.

Chris

 

[flecc]

Also your local Maplins store if you have one. It can be called contact cleaner or switch cleaner.

 

[Fordulike]

Thanks for the tip on the contacts, I'll give that a try! As far as aesthetics, I was actually thinking of putting the Ping battery inside the existing Cyclamatic enclosure. I haven't opened it to see if that's doable though, and I'm mostly curious about the 15AH version to make it worthwhile.

Sorry to burst your bubble, but not a chance in hell of fitting that 15Ah Ping in the casing.
Doubt if the 10Ah will fit either.
I've had the case open on numerous occasions and it's incredibly tight in there width and depth ways, although there is some room in the length/height dimension.
I reckon you might be able to fit one of those Ping batteries in the frame slot where the current battery goes, but how you would secure the battery in, is another matter.

P.S. I forgot to mention that another cause of problems with the original battery, is due to the amount of free space above the battery pack inside the casing. Any rough ground causes the pack to jolt up and down violently, hitting both the top of the case and also the bottom.
Unscrewing the top of the case and packing out the free space with foam, rubber etc.., will help prevent damage to the battery pack