Re: Bosch GRA53 36V Lawnmower - no motor
Nice idea, thanks. Easy and cheap too.
DanielCoffey
Senior Member
Last Activity: 09-02-2024, 04:17 AM
Joined: 12-31-2019
Location: South Ayrshire
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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.Last edited by DanielCoffey; 09-05-2023, 04:27 AM.Leave a comment:
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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...Leave a comment:
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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!...Last edited by DanielCoffey; 08-11-2023, 01:00 PM.Leave a comment:
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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.Leave a comment:
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Re: Bosch GRA53 36V Lawnmower - no motor
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....Leave a comment:
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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.Leave a comment:
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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.Leave a comment:
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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...Leave a comment:
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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...Last edited by DanielCoffey; 08-10-2023, 01:11 PM.Leave a comment:
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Re: Bosch GRA53 36V Lawnmower - no motor
I don't have that function on my multimeter, sorry. It is an ANENG AN8009Leave a comment:
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Re: Bosch GRA53 36V Lawnmower - no motor
Here is an update for the curious...
I managed to get the lower circlip out that held the lower bearing in place (in 2021 I fitted an SKF 25x47x12 Metal Shielded High Speed). There was a load of rust and the bearing had actually rusted solid. I deformed and levered the metal shields off and the contents were jammed with dirt and rust. After a soak in WD40 and a scrub with a brush I managed to rock the bearing free and flush it again.
Of course the mower did not function without the motor fitted. The LEDs on the...Leave a comment:
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Re: Bosch GRA53 36V Lawnmower - no motor
Unfortunately the cracked stator was preventing the blade from turning. Considerable force was needed to even get it to move. There was also signs of carbon on the inside of the motor and end cap. The Hall sensor board for monitoring rotation speed was covered in carbon too.
There is a slim chance that the Honda HRX 476 XB will use the same motor as it is based on the Bosch GRA46 (the smaller brother of what I have been using). Both mowers use the same battery format as Honda bought the rights from Bosch. There...Leave a comment:
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Re: Bosch GRA53 36V Lawnmower - no motor
Thank you but I disagree. Battery powered motors can handle fairly large areas now and are quieter and cheaper to run than petrol. Some of the higher powered ones can tackle anything that the larger single cylinder petrols were used for. There are some good all-electric riding mowers too that are based on Lithium.Leave a comment:
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Re: Bosch GRA53 36V Lawnmower - no motor
Well to be fair that rust was inside of the motor. The rest of the machine is fine. The body is powdercoated alloy and the fittings are stainless or coated.
I think most of the water leaked in past the cheap shaft seal and once inside started rusting the body of the motor. I suspect the cores in this type of brushless motors are simple iron or steel anyway.
While I could get the motor rebuilt and a new shaft seal fitted I don't want to spend that kind of money to find the electronics might not work. This is the unfortunate...Leave a comment:
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Re: Bosch GRA53 36V Lawnmower - no motor
Well folks - it is moot... the motor itself has failed due to corrosion and has a crack right across the stator.
It looks like there has been considerable water ingress over quite some time through the "shaft seal" (which is really only for impact protection). The lower bearing is rusted almost solid and is reluctant to turn. The top bearing under the end cap is in good condition but wet.
The permanent magnet rotor is wet, surface rusted but intact. A scotchbrite pad would have cleaned it up fine....Leave a comment:
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Re: Bosch GRA53 36V Lawnmower - no motor
This is the Shaft Seal that was covering the most exposed bearing. I was wondering if it was incomplete but I suspect it is just cheap.
When the mower was originally about two years old I noticed steam coming out from under the mower when cutting long and damp grass. The blade was turning roughly and this was the exact shaft seal that was in place at the time. There did not appear to be any rubber around the seal and there was about a 1mm gap between the seal and the shaft itself. Dirt and water had got into the original bearings...Leave a comment:
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Re: Bosch GRA53 36V Lawnmower - no motor
Well, as they would say in The South... I guess I owe y'all an apology!
The motor DID spin freely when I first examined the mower a month ago when it stopped working but since then it has totally siezed and will not turn now unless heaved.
I suspect a bearing has gone bad, rusted, triggered the fault due to the speed not matching the current supplied and shut down. Over the past month the mower has sat unused, the bearing has dried out and has rusted solid.
Fortunately I do know...Leave a comment:
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Re: Bosch GRA53 36V Lawnmower - no motor
I have not checked the motor supply or behaviour this morning yet but I have managed to identify through Google what the mystery two square modules are for that I asked about in the first post.
According to the Parts Diagram it is "91 - Diode Module" so presumably I can check if they are working correctly somehow? My multimeter does have a Diode setting. Does it have to be done in circuit or out?
Oh, and the potted modules are simply listed as either 887 or 888 - Electronics Moldule and come with a big...Leave a comment:
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Re: Bosch GRA53 36V Lawnmower - no motor
I will check the mower tomorrow as it is late here. I appreciate the advice on not applying battery voltage direct to the motor.Leave a comment:
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