Help! its dead pal - whats up with it ?

[beefsteak]

from time to time a bike seems to arrive thats been to every bike shop around and no one can fix it,
i'm not one to give up easily but sometimes i need a little help, here goes, this one is a 2014 wattoo electric bike originated in France so im informed with a silverfish 24 v battery
basically the problem is turn the key, led on bars light up and remain on till you try to pedal, theres a tiny surge forward , then its dead until you re initialise the key start procedure.
initially the bike came in the rear brake lever was solid and could not be operated, it also gave the fault of open circuit at brake sensor switch, replacing the cable fixed this issue, now lever sensors are ranging as they should, next issue was the chainset flopping around, adjusting the bottom bracket resolved this issue for now, the sensor on the bottom bracket appears to be working but the gap is around 3-4 mm with disc /sensor, battery charges and is solid at 29v, at the control unit it looks like its been through some water and signs of damp in back end of box , however, to replace that when that may not be the problem or if there is something fried elsewhere and blows a new control unit, i need some pointers please.

 

[cyclebuddy]

gap is around 3-4 mm with disc /sensor,

It's a sunny afternoon... all the usual e-bike experts that frequent this space will likely be out on their steeds. But that gap is too large - maybe 1-2mm would be more usual. Another oft-mentioned problem is dry joints on the key-switch giving intermittent/poor contact.

If you hang on a while, one of the proper e-bike mechanics will be along shortly...

 

[vfr400]

What do you mean by the battery being solid at 29v. Does it stay like that when the bike goes forward and cuts out, or do you only measure it before or/and after the event?

 

[beefsteak]

What do you mean by the battery being solid at 29v. Does it stay like that when the bike goes forward and cuts out, or do you only measure it before or/and after the event?

good point i'll test that situation.

 

[beefsteak]

What do you mean by the battery being solid at 29v. Does it stay like that when the bike goes forward and cuts out, or do you only measure it before or/and after the event?

hi and thanks for your reply, this afternoon i connected wires directly to the battery + & - terminals at bottom of battery and connected the corresponding ends to the Fluke 179, well i was really suprised initially, went for a ride and everything was working normally, till about 1 mile done, then the led's go off on the bike, i reinitialise at the key and nothing , after waiting for a minute retry sequence again and led's are back on and off we go, every time the voltage shown on fluke remains constant at 27/28 volts and then when the led go out plummets to 1v and after waiting for a minuter its back to 27 v to me sounds very much like an internal fault on battery, your thoughts ?

 

[wheeliepete]

Sounds like the voltage is sagging badly under load and the BMS in the battery pack is cuttin power. When it cuts out the voltage recovers and the BMS turns on again. It all adds up to a knacked battery, or at least one bad string of cells. The BMS monitors all 7 groups of series cells in the pack, so if one is bad, it cuts the power. If the pack is fairly old, this is the most likely cause. If you open the pack you can measure the voltage on each group of cells.

 

[vfr400]

There are two possibilities:
1. The battery is knackered and needs replacing. That will be so if it's an old and well used battery, though I'd expect to see the voltage go down by about 3V as soon as you start to draw power.
2. Connection fault, in particular, the soldering on the back of the key switch. It's fairly common to get dry or broken joints there. It's always worth resoldering them. Allow plenty of time to fully heat up and fuse properly. For a connection fault, the voltage would stay steady up to the point that the connection breaks.

 

[beefsteak]

There are two possibilities:
1. The battery is knackered and needs replacing. That will be so if it's an old and well used battery, though I'd expect to see the voltage go down by about 3V as soon as you start to draw power.
2. Connection fault, in particular, the soldering on the back of the key switch. It's fairly common to get dry or broken joints there. It's always worth resoldering them. Allow plenty of time to fully heat up and fuse properly. For a connection fault, the voltage would stay steady up to the point that the connection breaks.

so this morning i removed covers on battery, and i,m not surprised to find lots of previous repair work in top of battery around switch area, after speaking with customer and telling them my findings, the seller is going to be getting a visit.the cost of a new battery and the condition of bike makes the repair less appealing.
but a big thank you for your very kind help.

 

[wheeliepete]

so this morning i removed covers on battery, and i,m not surprised to find lots of previous repair work in top of battery around switch area, after speaking with customer and telling them my findings, the seller is going to be getting a visit.the cost of a new battery and the condition of bike makes the repair less appealing.
but a big thank you for your very kind help.

You can get a cheap 24v 10ah silvefish battery for around £100 on ebay, not gonna be the best quality, but would get the bike working.

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[vfr400]

Why didn't you repair the switch if it was faulty?