Bosch GRA53 36V Lawnmower - no motor

[stj]

Re: Bosch GRA53 36V Lawnmower - no motor

but they cost 3-5x as much

[petehall347]

Re: Bosch GRA53 36V Lawnmower - no motor

most of the broken ones i look at are not viable to repair . the control boards cost a lot or are not available .
the 80v stuff i dont have to look at too much . with them its batteries and chargers .

[eccerr0r]

Re: Bosch GRA53 36V Lawnmower - no motor

I'd imagine it should still work somewhat with the crack there? might run funny but should rotate.

I still use a lead acid mower that has a permanent magnet brushed motor. It's cheaper than the gasoline mower because I got it for the repair cost (was given to me nonfunctional with working battery). Was able to repair it and it's way cheaper than gas, minus the fact it takes longer to mow since it's a smaller mower...

I imagine the lithium ion mowers have enough specific power/capacity to run a wider cutting blade, but it's great not to have to change oil, fight with a clogged carburetor, deal with a cord, or buy gasoline...

[DanielCoffey]

Re: Bosch GRA53 36V Lawnmower - no motor

I'd imagine it should still work somewhat with the crack there? might run funny but should rotate.

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 are no parts diagrams of the Honda yet as it is too new but I can see the motor has the same housing as the Bosch one.

One major difference that is likely to be a showstopper is that the Bosch has a short shaft with the blade bolted directly to the end and moves via an independant rear axle electric motor. The Honda has a longer shaft with a belt drive pulley to the rear wheels. They are going to be incompatible I suspect.

I am using the Honda HRX 476 XB at the moment but there are several important differences. The cut is 46cm vs 53cm and I do have a large garden. The Honda uses the same batteries but takes only a single one at a time. While it is a matter of seconds to swap the battery (I have 4x 9Ah) the fact it draws from only one battery means it gets hot quickly. The Bosch used a pair in parallel so they ran cooler which was better for the batteries. Finally the narrow wheelbase of the Honda makes it jerkier over rough ground which is more effort to steer.

The reason I picked the Honda over other electric mowers is that I am invested in the batteries and two of them were very new with only a few charge cycles on them. The Honda does come with a 7 year non-commercial warranty which means I can use it until these batteries are worn out then consider changing to something completely different at that time.

[eccerr0r]

Re: Bosch GRA53 36V Lawnmower - no motor

oh well, since it appears to be more or less a total loss I'd still just grind it down so that it will at least turn and detect, even if it's not perfect, alas it's up to you. Not sure how long my motor will last, at least I try not to mow when wet.

[CapLeaker]

Re: Bosch GRA53 36V Lawnmower - no motor

oh well, since it appears to be more or less a total loss I'd still just grind it down so that it will at least turn and detect, even if it's not perfect, alas it's up to you. Not sure how long my motor will last, at least I try not to mow when wet.

Hahaha! I mowed 2 times this year dry. All the other times it wa soaking wet to the tune the rear finishing mower deck sunk in on a 4wd tractor. The zero turn would have totally got stuck down there. Our weather is the shits. Never seen anything like it here.

[DanielCoffey]

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 two control boards gave three fast flashes and shut down. Adding the cap with the Hall sensors did nothing new. Adding the motor body without the rotor did nothing. There is definitely a feedback from the Hall sensors that is required for power to be supplied to the motor.

Since all I wanted to verify was the control boards I reassembled the motor with the rusted bearing dry. Even a twitch or attempt to turn would show it was being controlled. The upper bearing was free and dry. The thrust spring and end cap went back on fine. The motor was free to turn although it was very rough.

Connecting the motor and sensor leads back to the mower gave exactly the same result as when the mower was siezed. Not a twitch out of the motor even though it is now free to turn followed by a whine, clicks and shutdown.

I connect the battery, press the master button and the red lights on the control boards turn on. Depressing the drive bar while lifting the rear allows the rear drive to engage and be controlled so that control board still works. The fault of a high-pitched whine for a few seconds and three clicks before shutdown is still present.

I removed the motor and checked continuity between the three legs. All three are low resistance (under 1 ohm). None of the legs make any connection to the case of the motor so there is no low voltage short.

I won't be able to find any information as to what the test or programming pins on the controller are for or what the clicks mean.

So, other than "the motor control board is knackered" are there any other ideas before scrapping it all?

[stj]

Re: Bosch GRA53 36V Lawnmower - no motor

can you meter inductance?
taking a Q reading from each winding would be good.

[DanielCoffey]

Re: Bosch GRA53 36V Lawnmower - no motor

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

[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

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

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 .

[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...

[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.

[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.

[stj]

Re: Bosch GRA53 36V Lawnmower - no motor

probably a longshot - look on aliexpress

[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

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

[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.

[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.