Fitting different battery to Gtech citybike

[rlawn]

Hi,

we bought a second hand Gtech Citybike two years ago for my wife and she is very happy with it, especially as lockdown eases off. But the already small (5.6Ah) battery has faded, and several of her friends have recently bought more powerful ones which means once they can cycle together again she will be dropping off half way!

It seems impossible to buy spare Gtech batteries (? unless someone can help - this is the old type with circular button, but I would be happy to adapt it to use the square button type).

Which means fitting a different battery, I guess a 10Ah one would do. As the controller is in the battery holder base on the Citybike this will involve some moving around of bits, but I am concerned about the electrical side. The Gtech controller has 4 wires running to the battery, see attached pic, the obvious red and black for power but the yellow and green ones for what? Clearly it will not be complicated for me to wire up the red and black from a non-Gtech 36V 10Ah battery, but I am asking for help with what will happen if yellow and green are not connected? Are they just wired to the switch on the battery (if so it is presumably solid state, so can it be replaced with a simple switch)? Or do they do something else?

Any assistance on either finding a (new) spare battery or on the wiring will be gratefully received

Richard

 

[Nealh]

Yellow and Green are two way comm's Tx/Rx between the controller and batteries BMS, without these the system will not work.
Replacing the battery with non GTECH one will need a new controller/ led or lcd and then then connect the motor up to it, depending on the motor connector type.

OR.

Two options easy one get Jimmy at BGA/Ebikebatteries .co.uk to recell the original with better cells and more capacity, if 24v it can be increased to 6.8ah or 36v to 10.4ah.

Second option is buy a generic battery of 5ah - 8ah & wire it up in parallel directly to the GTECH battery via a fly lead with an XT30/60 connector, this will then read as one larger battery capacity and use the gtech's batteries Tx/Rx comm's as the connection to the controllers comms wiring. You would need to exit the fly lead via the gtech battery case with a wire grommet and mount the new battery on a rear rack.

You should be able to wire the new battery in parallel via the controller base power supply and exit the fly lead directly out of the base, connect/switch on the old battery first so comm's are established then switch on the second battery to parallel them as one. The non generic battery would always have to be switched on last to connect and switched off first when disconnecting.

For charging both batteries would need disconnecting and charged separately.

A 24v 8.8ah battery < £150 or 36v one < £180 on ebay.

 

[Nealh]

My batteries don't use comm's between controller and BMS so I can parallel at the controller base, my comm's Tx/Rx only occurs between lcd & controller.

 

[rlawn]

Yellow and Green are two way comm's Tx/Rx between the controller and batteries BMS, without these the system will not work.
Replacing the battery with non GTECH one will need a new controller/ led or lcd and then then connect the motor up to it, depending on the motor connector type.

OR.

Two options easy one get Jimmy at BGA/Ebikebatteries .co.uk to recell the original with better cells and more capacity, if 24v it can be increased to 6.8ah or 36v to 10.4ah.

Second option is buy a generic battery of 5ah - 8ah & wire it up in parallel directly to the GTECH battery via a fly lead with an XT30/60 connector, this will then read as one larger battery capacity and use the gtech's batteries Tx/Rx comm's as the connection to the controllers comms wiring. You would need to exit the fly lead via the gtech battery case with a wire grommet and mount the new battery on a rear rack.

You should be able to wire the new battery in parallel via the controller base power supply and exit the fly lead directly out of the base, connect/switch on the old battery first so comm's are established then switch on the second battery to parallel them as one. The non generic battery would always have to be switched on last to connect and switched off first when disconnecting.

For charging both batteries would need disconnecting and charged separately.

A 24v 8.8ah battery < £150 or 36v one < £180 on ebay.

Thanks, that is very helpful, except for the bad news about Tx/Rx bit, which I must admit I had half expected I had thought about your parallel option and there is room for the new wire feed in the controller I think. My concern would be that if the existing 5.6Ah seems to be considerably reduced (it does a bit less than 10 miles now, versus 20 or more before) then adding in say 6 or 8 Ah might be a bit unbalanced?

So I will start with Jimmy, though approaches to other recell people have not worked (they don't do Gtech).

Thanks again

Richard

 

[Nealh]

Mention to Jimmy the comm's wiring as he will make sure the BMS is kept powered in case it shuts down if disconnected.

 

[rlawn]

Mention to Jimmy the comm's wiring as he will make sure the BMS is kept powered in case it shuts down if disconnected.

We have spoken, he knew about the comms, has taken a few apart. Have agreed for him to recell it, so thanks for the tip

Richard

 

[Atlav4]

Hi spare battery's do on occasion appear for sale on eBay but sadly command high prices Weighing 1.5kg not to bad for carrying to double your range

 

[Nealh]

Hi spare battery's do on occasion appear for sale on eBay but sadly command high prices Weighing 1.5kg not to bad for carrying to double your range

Over £300 for a silly 5.6ah battery is a joke, probably essential if you break the battery case but for a recell I expect about £140 - £200.

I had a softpack 15.6ah pack made up by Jimmy for £250 using the Boston 5200mah/13a cell.

If one has a case and good working BMS then a re- cell is a good cheaper option then buying new again as long as you aren't wanting more current from the new cells then the BMS can handle. In most instances capacity for the same amount of cells can be increased by about 25 -30%.

 

[rlawn]

Hi spare battery's do on occasion appear for sale on eBay but sadly command high prices Weighing 1.5kg not to bad for carrying to double your range

Thanks, we were looking... but the concern is they will also be a few years old, and so may have faded too..

 

[rlawn]

Over £300 for a silly 5.6ah battery is a joke, probably essential I you break the battery case but for a recell I expect about £140 - £200.

I had a softpack 15.6ah pack made up by Jimmy for £250 using the Boston 5200mah/13a cell.

If one has a case and good working BMS then a re- cell is a good cheaper option then buying new again as long as you aren't wanting more current from the new cells then the BMS can handle. In most instances capacity for the same amount of cells can be increased by about 25 -30%.

Thanks, yes that is what Jimmy is predicting, up to about 7Ah, hopefully all done in about a week's time Thanks again for the link.

 

[Nealh]

Looking at the GTECH case 20 cells looks like the max that can fit in so 3400/3500mah ones to replace the 2600mah ones, not quite the 10ah your wife's friends have but useful 33% capacity increase. To extend range try and get the wife to ride with no power on level ground, with the wind at her back or down hill, then she can save power for the inclines/hills and later on in the ride when energy levels are a little less.

 

[rlawn]

Looking at the GTECH case 20 cells looks like the max that can fit in so 3400/3500mah ones to replace the 2600mah ones, not quite the 10ah your wife's friends have but useful 33% capacity increase. To extend range try and get the wife to ride with no power on level ground, with the wind at her back or down hill, then she can save power for the inclines/hills and later on in the ride when energy levels are a little less.

to be honest I think the friends' bikes are bigger even than 10Ah, but if she goes from a faded 5.6 (probably more like 3-4) now to 7 I think we will be good. The friends' bikes are also big tyres etc and they do rough tracks, so if my wife really wants to start joining in we may need up with two bikes anyway but the citybike is great for shorter trips around town and road rides, and as it looks like a normal bike it feels much safer to leave locked to railings etc... I shall stick to sailing round the Irish Sea, once Wales lets me get back to the boat

 

[stevelo333]

I've used a non-Gtech battery on my esport..
1\ I put the Gtech battery in place, and made sure it was switched to full power, then switched it off and removed it.
2\ Then simply attached a different battery to the larger pair of terminals on the controller (having checked which was which by looking at the base of the Gtech battery which has + and minus symbols) with female spade connectors.

The bike runs exactly as it is meant to run. Absolutely no difference. So I think the two smaller terminals merely tell the controller which setting to use - full or eco. The upshot - use any 36v battery and it will be fine.

Incidentally, I used three 12v power tool batteries wired in series to make my own 36v 2Ah battery, as a back up to the Gtech battery, the range of which had dropped from 20 miles at full power (on a flat trail on a non-windy day) to about 12 miles (from pathetic to even more pathetic). A 2Ah battery is small and light, so not a bother to carry or fix to the bike alongside the original. But I'm considering better, permanent solutions.

 

[rlawn]

I've used a non-Gtech battery on my esport..
1\ I put the Gtech battery in place, and made sure it was switched to full power, then switched it off and removed it.
2\ Then simply attached a different battery to the larger pair of terminals on the controller (having checked which was which by looking at the base of the Gtech battery which has + and minus symbols) with female spade connectors.

The bike runs exactly as it is meant to run. Absolutely no difference. So I think the two smaller terminals merely tell the controller which setting to use - full or eco. The upshot - use any 36v battery and it will be fine.

Incidentally, I used three 12v power tool batteries wired in series to make my own 36v 2Ah battery, as a back up to the Gtech battery, the range of which had dropped from 20 miles at full power (on a flat trail on a non-windy day) to about 12 miles (from pathetic to even more pathetic). A 2Ah battery is small and light, so not a bother to carry or fix to the bike alongside the original. But I'm considering better, permanent solutions.

Thanks for atht info. We have actually had the existing battery recelled by Jimmy as mentioned above, it is working much better.

 

[Atlav4]

Sounds like a great solution to the small capacity Gtech battery. Having had the Escent I can vouch that range anxiety is prevalent, but left in max level permanently will lower the range of the substitute 36v battery quite significantly. Especially if travelling below 15.5mph for whatever reason (traffic stop starts or just bimbbling along) A 17ah battery weighs about 4kg adding significant weight to the bike and if you don’t pedal often over assist level then range would be 40-45 miles. Improvement yes but aesthetics are spoiled and carrying 2 stock batteries equates to 1kg less weight for little detriment in overall range.

 

[vfr400]

Yellow and Green are two way comm's Tx/Rx between the controller and batteries BMS, without these the system will not work.
Replacing the battery with non GTECH one will need a new controller/ led or lcd and then then connect the motor up to it, depending on the motor connector type.

OR.

Two options easy one get Jimmy at BGA/Ebikebatteries .co.uk to recell the original with better cells and more capacity, if 24v it can be increased to 6.8ah or 36v to 10.4ah.

Second option is buy a generic battery of 5ah - 8ah & wire it up in parallel directly to the GTECH battery via a fly lead with an XT30/60 connector, this will then read as one larger battery capacity and use the gtech's batteries Tx/Rx comm's as the connection to the controllers comms wiring. You would need to exit the fly lead via the gtech battery case with a wire grommet and mount the new battery on a rear rack.

You should be able to wire the new battery in parallel via the controller base power supply and exit the fly lead directly out of the base, connect/switch on the old battery first so comm's are established then switch on the second battery to parallel them as one. The non generic battery would always have to be switched on last to connect and switched off first when disconnecting.

For charging both batteries would need disconnecting and charged separately.

A 24v 8.8ah battery < £150 or 36v one < £180 on ebay.

I think Jimmy would have problems doing a Gtech battery because everything is glued in. You can always ask him. I'd chuck the entire electrical system except the motor, and fit a normal controller, then you can use any battery you want and go up to 48v to get a lot more power and speed, plus a much better control system. The whole lot would be cheaper than a replacement Gtech battery and a re-cell. A really nice controller, LCD and other stuff is about £70 and batteries go from £150 to £350 depending on voltage, size and quality.

BMSBattery are now selling these lightweight 7Ah batteries with a KT controller, LCD and the rest of the stuff included for about £260 inc shipping and tax

36V5Ah/7Ah HaiTu Bottle Battery Pack With USB Output Inner Controller With Cells / Capacity SAMSUNG 3.5AH / 7AH

HaiTu Bottle ebike battery pack 36V included a XT8 charger, It is also With USB Output.

bmsbattery.com

Or if you want more power and range, this one for about £380:

48V10Ah/11.6Ah/14Ah Bottle-09 E-Bike Battery & Charger Color White Inner Controller With Cells / Capacity 2.9AH / 11.6AH

New design bottle-09 e-bike battery pack 36V10Ah included a S180 charger.

bmsbattery.com

 

[stevelo333]

"I'd chuck the entire electrical system except the motor, and fit a normal controller.."

This is exactly what I plan to do - 48v as suggested, new controller, etc. I think this will make an OK bike into a real good 'un

 

[lharper]

Evening,
I brought my father a Gtech Sport a couple of years ago and he loves it. But the same as other the battery now has low range and £300 for a new one seems a but over the top. I have a Giant Trance with a 500wh batter and i have brought an 36v extender that take it up to 750wh. So I was thinking of just buying a 36v battery and adding that to the Gtech. So what controller and display combo would be people suggest ? I would say I have some basic understanding of what is needed. Just need to be pointed int he right direction if I am going to change to a new controller and display.

any advice welcome
Lee

 

[vfr400]

Evening,
I brought my father a Gtech Sport a couple of years ago and he loves it. But the same as other the battery now has low range and £300 for a new one seems a but over the top. I have a Giant Trance with a 500wh batter and i have brought an 36v extender that take it up to 750wh. So I was thinking of just buying a 36v battery and adding that to the Gtech. So what controller and display combo would be people suggest ? I would say I have some basic understanding of what is needed. Just need to be pointed int he right direction if I am going to change to a new controller and display.

You can use any 36v battery you want. I'd recommend a downtube one of some sort. There are a lot of options for controllers and the other stuff too. without gears, you're going to need around 18 to 20 amps. KT controllers give a good riding experience. You can get batteries with integrated KT controllers from BMSbattery and Topbikekit. The integrated controllers have the moulded waterproof connectors, which are nice and neat and easy to install, but I prefer the aluminium box type controllers with block connectors because they're easier to test when you get problems, but that means a separate box or bag to mount the controller in.

 

[Nealh]

KT are the most widely available 3rd party electronics, lots of places sell them and KT have cornered the kit market (good business sense) by making them freely available.