Bosch GRA53 36V Lawnmower - no motor

[DanielCoffey]

Re: Bosch GRA53 36V Lawnmower - no motor

Nice idea, thanks. Easy and cheap too.

[stj]

Re: Bosch GRA53 36V Lawnmower - no motor

maybe a big o-ring over the shaft and greased would help

[DanielCoffey]

Re: Bosch GRA53 36V Lawnmower - no motor

That's a good idea... the shaft is 25mm and there is a good 10mm of clearance (5mm each side). If I could find some 25mm ID thick walled hose I could cut enough that the blade would keep it in place but not long enough to jam it tight up against the seal. That would help keep the water out a bit better.

EDIT : it would interfere with the indent on the shaft for a 22mm spanner to assist with blade removal but it is a starting point to think about.

[sam_sam_sam]

Re: Bosch GRA53 36V Lawnmower - no motor

UPDATE : I wrote to Bosch asking whether I needed just a replacement motor or a control board as well. They advised given the symptoms that the control board appeared to be working as expected and to try just a new motor first.

I was mistaken when I quoted the motor power in an earlier post. I had assumed it was 1800W because that is the power of the one in my smaller Honda but the Bosch was only fitted with a 1440W motor.

One day I may try making a Frankenmower by combining the Honda 1800W motor and control board in the Bosch chassis but until then I have ordered and received a new 1440W Bosch 36V motor assembly.

It turns out that Bosch were correct - the control board does behave as expected and spins the new motor. It only does so briefly because I assume that without a blade it goes overspeed and shuts off. Once I have cleaned the chassis I will fit the motor and test it with the blade attached.

I do have one question though... the shaft seal. Bosch still only use an impact seal to prevent the lower motor bearing from being damaged by stones. It does not keep dirt or water out of the motor and even has a fairly wide gap between the seal and the shaft.

Given that the motor does not contain any oil or grease, is there a better type of seal that would keep the water and dust out of the motor? The dimensions without the Bosch impact seal are 37mm OD, 25mm ID and up to 6mm height. I also hav no idea of the correct way/tool for removing the existing impact seal which is pressed into place to cover the lower bearing and circlip.

I would not recommend that you try to remove the seal unless you plan on taking the motor apart here what I would do and recommend if have place where they make caskets for machines and equipment see if can get a rubber seal made at least 1/4” inch thick that will fit tight on the motor shaft and will cover the whole seal and over hang it at least a few mm this will help keep most of dirt and rocks from damaging the seal now you might have to use a hose clamp or glue the rubber to hold it up on the shaft

[DanielCoffey]

Re: Bosch GRA53 36V Lawnmower - no motor

UPDATE : I wrote to Bosch asking whether I needed just a replacement motor or a control board as well. They advised given the symptoms that the control board appeared to be working as expected and to try just a new motor first.

I was mistaken when I quoted the motor power in an earlier post. I had assumed it was 1800W because that is the power of the one in my smaller Honda but the Bosch was only fitted with a 1440W motor.

One day I may try making a Frankenmower by combining the Honda 1800W motor and control board in the Bosch chassis but until then I have ordered and received a new 1440W Bosch 36V motor assembly.

It turns out that Bosch were correct - the control board does behave as expected and spins the new motor. It only does so briefly because I assume that without a blade it goes overspeed and shuts off. Once I have cleaned the chassis I will fit the motor and test it with the blade attached.

I do have one question though... the shaft seal. Bosch still only use an impact seal to prevent the lower motor bearing from being damaged by stones. It does not keep dirt or water out of the motor and even has a fairly wide gap between the seal and the shaft.

Given that the motor does not contain any oil or grease, is there a better type of seal that would keep the water and dust out of the motor? The dimensions without the Bosch impact seal are 37mm OD, 25mm ID and up to 6mm height. I also hav no idea of the correct way/tool for removing the existing impact seal which is pressed into place to cover the lower bearing and circlip.

[DanielCoffey]

Re: Bosch GRA53 36V Lawnmower - no motor

Here we go - this is what is on the board inside the motor. Three Hall Effect W32 transistors by the looks of it?

EDIT : If you were asking about the power circuit driving the motor, that is under the black resin in the lower module on the chassis. No way of knowing what the heck is under that lot!

[DanielCoffey]

Re: Bosch GRA53 36V Lawnmower - no motor

There is a PCB, yes, but the components on it are tiny. Let me get some pictures of it in case it is useful. I thought it was the Hall effect rotation sensor but I am probably incorrect.

[petehall347]

Re: Bosch GRA53 36V Lawnmower - no motor

is there a pcb inside the motor with fets etc ?

[DanielCoffey]

Re: Bosch GRA53 36V Lawnmower - no motor

Did the magnet pull the rotor to contact the field magnets?

I have no idea but something is heating the supply cable so I am not going to try again. There does not seem to be excessive play in the old bearings - they are just very rough.

[eccerr0r]

Re: Bosch GRA53 36V Lawnmower - no motor

Did the magnet pull the rotor to contact the field magnets?

I'd think watt is watt, but don't know about what power your mower uses, probably a lot more than mine. Mine's only 1/3 HP I think, hence the smaller cutting blade.

[stj]

Re: Bosch GRA53 36V Lawnmower - no motor

hmmm.
but maybe it makes less than it consumes?
i'm not an expert on motor/generator power

[DanielCoffey]

Re: Bosch GRA53 36V Lawnmower - no motor

Funny you should suggest that but I have actually seen a fair few brushless motor cores on there, mainly for homemade wind turbines. Sadly they either have inflated claims of their rating or, if honest, are too low for this use case. One which was the correct dimension offered 650-750W but, according to Bosch and Honda I need one which is 1800W.

[stj]

Re: Bosch GRA53 36V Lawnmower - no motor

probably a longshot - look on aliexpress

[DanielCoffey]

Re: Bosch GRA53 36V Lawnmower - no motor

Update : the whine and three clicks are coming from the motor itself. I could feel the slight "clunk" in the motor housing when it happened but no rotation. In addition one of the motor leads (yellow out of black/yellow/green) was getting hot.

Given that I now know power is being supplied to the motor I think it might be useful to investigate the cost of a motor rebuild.

[DanielCoffey]

Re: Bosch GRA53 36V Lawnmower - no motor

The wheel drive works perfectly, yes. That control board is working as intended and listenes to the handlebar speed control and drive bar.

All four batteries are fine and can be tested in both other Bosch equipment and a multimeter.

The motor spindle doesn't even twitch. I have temporarily ziptied the "child-proof" switch into the run position since it is awkward to hold when the case is off. I connect a battery, press the handlebar side switch and then hold the bar to the run position. Instantly I see a red LED on both control boards, the motor board makes a high pitched whine then there are three slow (1s interval) clicks then everything shuts down. There is no twitch from the spindle and there is no feeling of drag or movement if I try to rotate it in either direction during any stage of this process.

[eccerr0r]

Re: Bosch GRA53 36V Lawnmower - no motor

What are the "wheel" connections? Does that still work? Sure your batteries are still good? Not a twitch in the motor spindle at all?

Anyway weird that the controller would kill itself with a seized motor when there's also a tachometer sensor...

[petehall347]

Re: Bosch GRA53 36V Lawnmower - no motor

i tried that with a brushless motor and same result .. only result i got was spinning it with a drill and measuring voltages across windings which were all exactly the same . bit if a pain it was removing the internal board inside the motor .. i never got that one working as new parts were costing more than a new tool .

[DanielCoffey]

Re: Bosch GRA53 36V Lawnmower - no motor

The motor makes no movement at all - nothing.

All I get is the whine then three clicks. Is there a common list of clicks or beep codes for these type of boards?

EDIT : I just watched a video on brushless motor testing and it suggested disconnecting the motor and jumping one pin on the main motor lead to another and checking for effort required to rotate the motor compared to no connection then repeating this on each leg. In my motor there is no change in the effort required to spin the motor when any pairs are joined.

[petehall347]

Re: Bosch GRA53 36V Lawnmower - no motor

one thing if the motor twitches or spins and then stops it can be the control board ..last mower i looked at did just that .it beeped 3 times as well .not that i take much notice of the bleeps .

[DanielCoffey]

Re: Bosch GRA53 36V Lawnmower - no motor

I don't have that function on my multimeter, sorry. It is an ANENG AN8009