Gtech ebike City damaged in fire!

[Mefmotorsport]

I've r-posted this to create its own thread.

Hi all,

I have 2 Gtech city ebikes which were recently subjected to intense heat in a serious garage fire at home. The bikes have fared pretty well, just smoke damaged really but one had its battery fitted which has partially melted and has since failed completely. The bikes both work fine on the other good battery which was in the house. I rang Gtech about buying a replacement V1 battery but they don’t sell them any more so the bike is useless. They don't sell any parts to upgrade it to their V2 battery either.

I was thinking about fitting an aftermarket battery and controller (I am an electronics engineer so I’m not daunted by this task) so I’m interested in anyone’s thoughts on such a conversion.

I see that the motor controller circuitry is enclosed in the battery holder and there is considerable circuitry inside the battery too. As I undrstand it the motor is much like any other, presumably 3 wires like a 3 phase AC motor?

If I don’t sort something out then the bike is scrap which is a shame as it was superb for me and my wife’s requirements, taken to France a couple of times on rear of our Motorhome.

It looks like the Insurance company will probably write them off in which case I will be free to modify them as I like this could be an interesting project. maybe I can improve them at the same time. I've so far taken a battery apart and started to learn about them, I can see that the battery negative is switched by 3 mosfet devices to the output connector. Im not sure what the 2 middle pins do though, presumably some kind of detection or feedback circuit controlling the output current?

Any comments welcome!

 

[Nealh]

Most of the bottle type like you have with the base controller are normally OEM items, they tend to be low power/capacity.
Yes the likes of GTECH use handshaking between components so you are tied in to them.
After market kits, batteries & controllers etc,etc, don't use those components so you can use any battery or controller. With controllers though you do have to use the same brand of LCD as they do use communication protocols between each other.
Battery wise though they just use two power wires for simplicity.

 

[Mefmotorsport]

Thanks for advice, yes, I can easily modify the battery so it just gives a solid 36v output on the 2 pins, that’s no problem, So I will need some kind of controller to drive the motor (3 phase?) and presumably I can use the existing pedal crank sensor , maybe I’ll need a throttle and maybe a brake switch?

I’ll investigate the pedal signal to see what it does, not sure if it’s a magnetic inductive pickup or maybe a Hall effect type with 3 wires.

 

[Nealh]

You don't need to modify after market batteries they are only two pin discharge.
You need to see how many motor wire there are, there will be three DC phase wires but also you need out find out if there are 5 or 6 hall sensor wires as well.
If the motor is sensor less then you need a square wave controller.
If it is sensored you need sinewave sensored controller.
Plenty of options about also if you want Torque sensor over cadence sensor then that is an option as well.

 

[Nealh]

I’ll investigate the pedal signal to see what it does, not sure if it’s a magnetic inductive pickup or maybe a Hall effect type with 3 wires.

With ebikes it is the same thing.
The sensor uses a hall which needs a magnet disc to act as the signal pulse.

 

[Mefmotorsport]

You don't need to modify after market batteries they are only two pin discharge.
You need to see how many motor wire there are, there will be three DC phase wires but also you need out find out if there are 5 or 6 hall sensor wires as well.
If the motor is sensor less then you need a square wave controller.
If it is sensored you need sinewave sensored controller.
Plenty of options about also if you want Torque sensor over cadence sensor then that is an option as well.

I meant the standard Gtech ebike battery, although it doesn't work correctly there's nothing wrong with the battery cells, I can just link out the control circuit so it always gives out 36V. I'll have to cut into the motor wire outer sheath to see how many are inside. The pedal sensor comes from inside the crank bottom bracket, its very thin, it goes up to the motor controller which is the actual battery mount.

 

[wheeliepete]

I can just link out the control circuit so it always gives out 36V.

You may wish to fit a new BMS to keep the battery balanced and will prob. need a new generic charger.

 

[Mefmotorsport]

You may wish to fit a new BMS to keep the battery balanced and will prob. need a new generic charger.

I just pulled the connector apart on the motor cable and was surprised to find that there was 8 pins, 3 thick ones, presumably the 3 motor phase connections then a further 5 thinner pins. Is this a standard motor configuration or specific to Gtech Ebikes?

 

[Nealh]

No quite standard nowadays you have hall sensored/sinewave hub without internal speed sensor, a lot of modern hubs also use a ninth wire for speed sensing.
I did mention it in #4.

If the GTECH doesn't use a display then it has no need for a hub with a speed hall, if you change controller and want an lcd which will have odo reading you simply use a speed sensor with magnet to the rear wheel and wire it to the controller pcb or controller wiring dependant on the type of wiring the controller has. Some use water proof sealed connectors and some use JST Sm connectors.

 

[Mefmotorsport]

No quite standard nowadays you have hall sensored/sinewave hub without internal speed sensor, a lot of modern hubs also use a ninth wire for speed sensing.
I did mention it in #4.

If the GTECH doesn't use a display then it has no need for a hub with a speed hall, if you change controller and want an lcd which will have odo reading you simply use a speed sensor with magnet to the rear wheel and wire it to the controller pcb or controller wiring dependant on the type of wiring the controller has. Some use water proof sealed connectors and some use JST Sm connectors.

So I would just use the 3 phase connector pins and ignore the rest then. The Gtech eBike doesn’t have an lcd display, the only other wire is the sensor in the pedal hub, that plus the 8 pin connector from the motor both connect to the motor controller unit. So I assume I’d use an external motor controller and hopefully utilise the existing pedal sensor? Can you suggest a suitable controller and lcd display, it looks like a minefield! Cheers

 

[Nealh]

No if you want the quietness softer tones of the sensored motor you would connect the sensor wires up to a sensored/sinewave controller.

The best after market set up is KT/Kuenteng make.

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