36V Bosch tool battery for e-bike use

[peterjd]

Well it looks like summer is over, so it's back to sorting my 'cave' and as a first step, doing something with the (good) 18650 cells I recovered some time back from a prematurely dead Swytch Mk 1 battery pack. They still look good(?) after sitting some months as single cells at about 3.4V (ie after discharge test).

Now that I am regularly using 36V Bosch lawnmower/tool batteries for local trips on my converted touring bike - I have acquired a total of 4 genuine + 1 look-alike batteries - I am wondering could I safely piggy-back a selected set of the spare 18650s onto a genuine Bosch battery for use (and charging with a genuine Bosch charger)?

Has the missing BMS on the Bosch batteries been solved? Is it a matter of hand balancing cell sets?

 

[StuartsProjects]

On the older lower capacity packs, there is no BMS, but there is a temperature monitor.

I seem to recall seeing a picture of the battery controller board for the more modern 6AHr battery and that appeared to have wires to each cell group, which the lower capacity batteries do not have. However it seems unlikley that the 6Ahr battery does do balancing, although it possible it detects balance errors and reports through the central battery connector.

I have seen people using these batteries with just the power connectors but that implies that any error the battery controller board detects is not picked up. Presumably if the battery detects an error it signals that error so that the power tool can stop powering the motor.

For eBike use I would suggest that you need to implement some form of switch off of the eBike motor, say via a brake switch sensor input, if the battery reports a fault. To do that you need to work out the signal protocol that the battery uses.

I guess it depends how lucky you feel.

 

[benjaminkelenyi]

Hello guys. Thanks a lot for sharing all the information; it is very useful.

I bought a mower (easy-rotak 36-550) but without a battery. I created a custom battery for the machine, but the problem is that it doesn't start. I figured out that the main issue is that I do not have the middle pin connected to the machine.

With an original Bosch battery, the mower works as expected.

Do you know how it is possible to bypass the middle pin (BUS)? Is there a workaround?

Thanks a lot!

 

[StuartsProjects]

Do you know how it is possible to bypass the middle pin (BUS)? Is there a workaround?

You would need to replicate the control unit inside a Boch battery that the mower expects to see.

Sounds like a question for a lawnmower or power tool forum.

 

[WheezyRider]

You would need to replicate the control unit inside a Boch battery that the mower expects to see.

Sounds like a question for a lawnmower or power tool forum.

I wonder if you just took a control board from a dead Bosch battery and connected it in parallel to the DIY pack whether it would provide the centre pin signal? All it seems to do is monitor temperature and if that's at room temperature, it wouldn't report an error.

 

[Woosh]

Do you know how it is possible to bypass the middle pin (BUS)? Is there a workaround?

I wouldn't do that. Your mower needs to know that the battery is working in its safe zone. If you gives it false information, something bad may happen.
Yesterday on BBC Breakfast, there was a call for mandatory third party testing of batteries and making compulsory that the battery talks to the charger before accepting charge to reduce risk of overcharging.

 

[StuartsProjects]

All it seems to do is monitor temperature and if that's at room temperature, it wouldn't report an error.

Problem there of course is that if the battery starts to overheat whatever its powering wont cut out.

 

[benjaminkelenyi]

I wonder if you just took a control board from a dead Bosch battery and connected it in parallel to the DIY pack whether it would provide the centre pin signal? All it seems to do is monitor temperature and if that's at room temperature, it wouldn't report an error.

Not at the moment.

My battery pack includes a BMS equipped with a thermistor, which means that the BMS will handle the temperature monitoring.

 

[benjaminkelenyi]

I wouldn't do that. Your mower needs to know that the battery is working in its safe zone. If you gives it false information, something bad may happen.
Yesterday on BBC Breakfast, there was a call for mandatory third party testing of batteries and making compulsory that the battery talks to the charger before accepting charge to reduce risk of overcharging.

I agree with you, but my battery pack has a BMS with a temperature sensor, so I assume it's safe because the BMS will monitor and handle any overheating.

 

[benjaminkelenyi]

You would need to replicate the control unit inside a Boch battery that the mower expects to see.

Sounds like a question for a lawnmower or power tool forum.

Yes, this is a good idea. I had considered replicating the BUS signal using an Arduino Nano, but I'm not certain about the signal's specifics. It would be ideal to capture the signal using a logic analyzer before attempting to replicate it, but unfortunately, I don't have a working Bosch battery to monitor the signal.

 

[WheezyRider]

Problem there of course is that if the battery starts to overheat whatever its powering wont cut out.

I agree. I am assuming that the OP knows what they are doing, has built the battery to a suitable standard, to be able to supply enough current, is properly fused and has its own BMS with thermal cut out etc etc.

 

[WheezyRider]

Yes, this is a good idea. I had considered replicating the BUS signal using an Arduino Nano, but I'm not certain about the signal's specifics. It would be ideal to capture the signal using a logic analyzer before attempting to replicate it, but unfortunately, I don't have a working Bosch battery to monitor the signal.

You can buy the Bosch battery style board for about £20, or you can pick up a dead battery quite cheaply and obtain a genuine board from that.

 

[Woosh]

I watched a yt video last night about tool batteries. The main theme is there are 2 signals, one to start the battery and one to stop it. Those batteries can supply insane currents, much higher than those we see on E-bikes. The guy pumps 75A from his tool battery. So if you want to use your battery on tools, watch the current, otherwise you'll kill your cells in no time.

 

[WheezyRider]

I watched a yt video last night about tool batteries. The main theme is there are 2 signals, one to start the battery and one to stop it. Those batteries can supply insane currents, much higher than those we see on E-bikes. The guy pumps 75A from his tool battery. So if you want to use your battery on tools, watch the current, otherwise you'll kill your cells in no time.

There is a fuse on the Bosch battery, which I forget the rating (I think it has been mentioned in this thread) although it is a lot less than 75A. But yes, the OP does need to be sure that the batteries they have chosen for their DIY pack can handle the kind of currents to be expected from the mower.

 

[Woosh]

it's still worth considering using a tool battery for e-bikes.
You can build a good and cheap e-bike using my BBTS kit (£100), a motorwheel and a tool battery.

 

[WheezyRider]

it's still worth considering using a tool battery for e-bikes.
You can build a good and cheap e-bike using my BBTS kit (£100), a motorwheel and a tool battery.

The concerns I have with this are that with some of the Bosch batteries (it seems particularly the older versions) have only a very primitive monitoring system that only looks at temperature, with no balance, no undervoltage protection (maybe in the COMs protocol to the tool, or the tool just senses undervoltage? But certainly no individual cell undervoltage protection), no short circuit protection (other than a high rating fuse)...and without the COMs set up in some way with the e-bike controller, there is no way to monitor temperature etc. The other thing is that the packs are not at all waterproof. They are full of vents for cooling. I've seen some people selling a waterproof sock for them, but this then covers up the cooling vents!

 

[Woosh]

the risk of damaging the tool battery when used to power ebikes is much less than the other way round, using your bike battery to power a lawnmower for example. The LVC is set in the controller, usually 31.5V. The overcurrent is usually non existent, controllers are usually set for 15A max. The remaining risk is water and temperature. Temperature risk is usually non existent if ventilation is adequate, like mounting it to my Brompton luggage block or downtube.

 

[WheezyRider]

the risk of damaging the tool battery when used to power ebikes is much less than the other way round, using your bike battery to power a lawnmower for example. The LVC is set in the controller, usually 31.5V. The overcurrent is usually non existent, controllers are usually set for 15A max. The remaining risk is water and temperature. Temperature risk is usually non existent if ventilation is adequate, like mounting it to my Brompton luggage block or downtube.

Over current is usually not an issue unless someone tried to run a 20 A plus controller on a tool battery not designed for that kind of draw...or a MOSFET goes down in the controller - I've had that happen before.

I do worry about the lack of individual cell monitoring. If one cell is weak, the others gang up on it, dumping lots of heat into that one cell until it fails with rupture/fire. This has almost happened to me when back in the early days, I ran a small pack without a BMS to power a bike. I pulled the plug when the shrink wrap started melting on some cells and caught it just in time. If there is no balancing, it is more likely that some cells may end up weaker than the rest.

The later Bosch packs do seem to have individual cell monitoring, so the recommendation may be to get a later one, rather than an older one.

Still need to solve the issue of water proofing/resistance though....

 

[Woosh]

it may be still worth considering for infrequent use compared to the cost of a full kit.

 

[WheezyRider]

it may be still worth considering for infrequent use compared to the cost of a full kit.

Agreed, but maybe the way to go is the Einhell route rather than Bosch. Einhell have everything contained in the tool battery and you are not reliant on tool/battery COMs. However, the Einhell set up only uses 18 V packs, so you have to use 2 in series.