Assist cuts out occasionally

fudoka

Finding my (electric) wheels
Nov 20, 2018
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It's happened several times now, the assist just stops. If I turn the battery off, wait for a minute or so and turn it back on again it comes back on. The controller display shows the battery still full, in fact the display doesn't change at all when it cuts out. Just turning the system off from the controller doesn't seem to reset the system, it has to be switching the battery off and on again
So far it's been after I've climbed a hill but never with maximum assist and, fortunately, within metres of reaching the top or just after.
All the connections appear to be solid but the battery is getting on a bit (but not heavily used).
The bike is a Joe Tern converted with a Bafang rear-wheel driver kit from Woosh which has been pretty good so far.
Does anyone have any idea what could be causing this? I know the battery is getting a bit long in the tooth but it seems to be holding charge pretty well still.
 

Benjahmin

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Nov 10, 2014
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How old is the battery?
The battery may be holding charge but., with age, internal resistance increases. What this does is to increase voltage sag when power is drawn. Despite you not increasing assit level, the amperage called for when climbing hills will increase. This heats up the cells with higher resistance so increasing the resistance more leading to voltage sag. When voltage dips below low volt cutoff the system is shut down.
If you have a volt meter you can measure the battery voltage hot off the charger. It should be 41.7v for a 36v battery. Any less will show potential ageing problems
 

Nealh

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Aug 7, 2014
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If it only occurs on hill climbs then battery voltage sag is the cause, when the voltage sags it hits the battery BM LVC so the power will cut out. A fully charged battery can usually deal with it but once the battery voltage reduces thru use then the likelyhood is and older battery will cut out.
Do you know the battery voltage reading before the power cut outs ?

Voltage sag rebounds once demand(current draw) on it is reduced , climbing a hill puts a demand on the battery for a longer period .
 

thelarkbox

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Aug 23, 2023
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if the display shows no sign of an issue?? does it show any indication if/when brake sensors are tripped?

I would try and replicate the problem with no throttle or brake sensors attached only the psa or torque sensor and if the problem persists exchange the pas sensor.
 

Nealh

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Does anyone have any idea what could be causing this? I know the battery is getting a bit long in the tooth but it seems to be holding charge pretty well still.
A replacement/new battery will solve the issues or choose less hilly routes , it is a simple fact of science that batteries will age, once they age they simply can't deliver the performance as when they are new.

Internal cell resistance and heat are part of the ageing process of a battery and something one can't do much about .
 

saneagle

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Oct 10, 2010
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It's happened several times now, the assist just stops. If I turn the battery off, wait for a minute or so and turn it back on again it comes back on. The controller display shows the battery still full, in fact the display doesn't change at all when it cuts out. Just turning the system off from the controller doesn't seem to reset the system, it has to be switching the battery off and on again
So far it's been after I've climbed a hill but never with maximum assist and, fortunately, within metres of reaching the top or just after.
All the connections appear to be solid but the battery is getting on a bit (but not heavily used).
The bike is a Joe Tern converted with a Bafang rear-wheel driver kit from Woosh which has been pretty good so far.
Does anyone have any idea what could be causing this? I know the battery is getting a bit long in the tooth but it seems to be holding charge pretty well still.
If the battery was knackered, you should see the battery sag down on the LCD before switching off. The LCD would definitely switch itself off, but you say it stays on. I'd say that the first thing to check is the motor connector. make sure that it's pushed together ALL THE WAY TO THE MARKED LINE, not just in tight. Other than that, the software must have detected that something has gone out of range. Do you have a throttle?
 

Nealh

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Aug 7, 2014
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Good point I over looked, yep if the display remains on then the fault is likely elsewhere.
 

Sturmey

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Jan 26, 2018
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I had a similar problem caused by the dirt in the pedal assist sensor causing the magnet disk to seize and slip on the crank.
 
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Woosh

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Does anyone have any idea what could be causing this? I know the battery is getting a bit long in the tooth but it seems to be holding charge pretty well still.
if the LCD stays on when the motor cuts out, it's probably the controller or one of the sensors. Try unplugging the throttle and brake sensors. If the problem does not go away, please get in touch with support@wooshbikes.co.uk - Andy will help you sort it.
 

peterjd

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Sep 18, 2019
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I've had a similar sort of effect with my adapted Swytch setup and (I think) only when using the Yose battery. The display has not gone off and after a couple of hundred yards of harder cycling the assistance has come back on. It's a different sort of connection to the Yose battery so I have put it down to that and/or the battery has not 'warmed up'. I will investigate if it becomes more troublesome.
 

fudoka

Finding my (electric) wheels
Nov 20, 2018
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If the battery was knackered, you should see the battery sag down on the LCD before switching off. The LCD would definitely switch itself off, but you say it stays on. I'd say that the first thing to check is the motor connector. make sure that it's pushed together ALL THE WAY TO THE MARKED LINE, not just in tight. Other than that, the software must have detected that something has gone out of range. Do you have a throttle?
Yes, I have a throttle - that dies at the same time though.I did quickly check all the connectors to see if any could have worked loose but I'll go over them again in more detail just to make sure.
 

fudoka

Finding my (electric) wheels
Nov 20, 2018
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A replacement/new battery will solve the issues or choose less hilly routes , it is a simple fact of science that batteries will age, once they age they simply can't deliver the performance as when they are new.

Internal cell resistance and heat are part of the ageing process of a battery and something one can't do much about .
I'm in East Crete (Skopi village, just outside Sitia) - there are no less hilly routes :). Getting a replacement battery is more of a problem post Brexit but Woosh! (bless them) have offered to send me a replacement and reckon that the courier will handle the shipping documents.
 

fudoka

Finding my (electric) wheels
Nov 20, 2018
21
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73
if the LCD stays on when the motor cuts out, it's probably the controller or one of the sensors. Try unplugging the throttle and brake sensors. If the problem does not go away, please get in touch with support@wooshbikes.co.uk - Andy will help you sort it.
Thanks for the suggestion - will try that but it does sound like an aging battery problem.
I'm in Crete and the original conversion was pre-Brexit so it is getting a bit long in the tooth. It's just that the bike is not heavily used and then only for short (<15Km) journeys so replacing a battery just by age gets a bit expensive on the €/Km basis.
At 73 I need the assist to climb the steep hills in the area. 15% - ha! that counts as a gentle slope round here ;-).
 

Nealh

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How fast do you pedal up hill when the power cuts out ?
 

fudoka

Finding my (electric) wheels
Nov 20, 2018
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How fast do you pedal up hill when the power cuts out ?
As I say, I've been lucky in that the assist cut-out has happened (so far) either just after or just before the top of the hill. Given the hills round here (E. Crete) and me being 73 I can tell you it'll be bl**dy slowly :) - or rather I'm pedalling fairly fast but in the lowest gear available so travelling pretty slowly.
 

saneagle

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Oct 10, 2010
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As I say, I've been lucky in that the assist cut-out has happened (so far) either just after or just before the top of the hill. Given the hills round here (E. Crete) and me being 73 I can tell you it'll be bl**dy slowly :) - or rather I'm pedalling fairly fast but in the lowest gear available so travelling pretty slowly.
In that case It's probable that your controller is over-heating and the thermal cut-out is activating. If you can, have a feel of the controller after cut-out to see how hot it is.

There are three potential solutions to overheating, but do the test first because everything below will be moot if it doesn't get hot. Maybe, exposing it to the air in order for you to test it will be enough to solve the problem.

First is more speed by increasing the power, which can be done at zero cost by soldering the shunt to get more current. That's worth trying before buying buying a new controller because it doesn't cost anything, though there's a chance it can make it worse, depending on the speed you get.

The second is to get more air flowing over the controller. When I tried that, it had minimal affect, but if your controller is in a box, a fan might make a big difference. Anything to get more air will help.

Third is to buy a new bigger controller that can handle heat better. Bigger controllers generally allow more current. If your battery is tired, it might not be able to give much extra, but some controllers allow you to adjust the current in the settings to cover that.
 

Nealh

Esteemed Pedelecer
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Controller thermal cut out of the mosfets was my second thought on reading the #1 again, having previously not read it properly.
Hence asking the climbing speed.
I know when I had thermal cutitng out riding the South Downs, I too was riding too slowly for the steep sections I came across.
Heat sinks I tried first but to no avail , then a pair of small 5v fans helped but I soon tired of remembering to charge the 5v battery packs. In the end I swapped out the 6 fet KT for a 9 fet model and it solved my issues.

Be careful if one attempts to handle the controller following a thermal cut out , they are so hot that they will cause hand scalding.
 
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Benjahmin

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Nov 10, 2014
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I too have suffered thermal cut out. There is one climb in particular that is about 1.5 miles long. It starts gently under trees but, as you emerge from the trees into full sun, it gets gradually steeper, so I get gradually slower. It can cut near the top in warm weather. The controller body is too hot to hold at that point.
 

fudoka

Finding my (electric) wheels
Nov 20, 2018
21
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73
In that case It's probable that your controller is over-heating and the thermal cut-out is activating. If you can, have a feel of the controller after cut-out to see how hot it is.

There are three potential solutions to overheating, but do the test first because everything below will be moot if it doesn't get hot. Maybe, exposing it to the air in order for you to test it will be enough to solve the problem.

First is more speed by increasing the power, which can be done at zero cost by soldering the shunt to get more current. That's worth trying before buying buying a new controller because it doesn't cost anything, though there's a chance it can make it worse, depending on the speed you get.

The second is to get more air flowing over the controller. When I tried that, it had minimal affect, but if your controller is in a box, a fan might make a big difference. Anything to get more air will help.

Third is to buy a new bigger controller that can handle heat better. Bigger controllers generally allow more current. If your battery is tired, it might not be able to give much extra, but some controllers allow you to adjust the current in the settings to cover that.
First I have to work out where the controller is ;). It's a rack-mounted battery and, if I'm right, the controller is built into the battery cradle.
I haven't checked this when it cuts out but, since I turn the battery on/off to reset I'd have thought I'd have noticed if there was a lot of heat in the area - even though the power switch is at the opposite end of the cradle. I'll try and remember to check it next time it happens.
I use a rack-top bag and I cycle in a Cretan summer so, if excess heat is the cause, I'm really going to have to do some thinking ...