Hi folks. I have a Bosch GRA53 36V lawnmower that has developed a fault and will not spin the blade.
I should say for the purposes of guiding what how you can explain things to me that that I have only modest knowledge of electronics, own a basic multimeter and soldering iron.
The mower is four years old, out of warranty, discontinued and the brand has been sold to Honda who have iterated on the design a couple of times and now sell their own 36V mower. My mower was effectively a prototype when Bosch tried the 36V Bosch Professional range of garden equipment which all used their proprietary 36V 4.5Ah, 6Ah and 9Ah batteries. It never sold well and was discontinued very shortly after I bought it along with two of the 9Ah batteries.
New the mower cost around £1600 and the 9Ah batteries were £400 each. The mower uses two of the 36V 9Ah batteries in parallel for 36V and 18Ah capacity.
Last year I began to notice a deterioration in the battery capacity. I discovered the range was discontinued but found it had been sold to Honda who were producing their own tools using the exact same battery format. I bought two more 9Ah batteries for £300 each and resumed using the mower.
About a month ago the mower cut out during use but resumed correctly. I finished the cutting, washed under the deck and put it away.
The next time I went to use it, the mower would not start.
The "child proof safety key" is in place. This interrupts the main battery positive.
The blade spins freely and does not feel unusual.
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FAULT DESCRIPTION
When holding the "start" button on the handlebars and holding the bar against the handle no power is sent to the motor. There is just a high pitched whine for a couple of seconds, a pair of faint clicks one second apart then nothing. The fault is consistent with either both batteries or just one battery in either slot.
===
Having opened the top case of the mower I can see all wiring connectors appear normal. Nothing appears out of place or burned. I can understand what most of the cables are for and have identified a few of the components. While there are red indicator LEDs on the two boards, all components are buried under black potting compound (of course). There are some test or programming pins protruding from the compound.
I have been following how the mower has been designed and can see the pair of parallel battery positives go to each side of the child-proof switch. Each side then goes to a pair of square components which I do not understand. I have not removed them to see if there are any markings on the other side. If they are fuses then I am confused as to why there are two of them running in series.
Because there are a pair of wires running from each battery direct to each potted board, the boards sense the batteries and power up, showing a steady red LED as soon as the safeties of child lock, side button and handle bar are set.
So, first question, does anyone recognise the symptoms and what are the two square modules I have highlighted in the second image please?
I should say for the purposes of guiding what how you can explain things to me that that I have only modest knowledge of electronics, own a basic multimeter and soldering iron.
The mower is four years old, out of warranty, discontinued and the brand has been sold to Honda who have iterated on the design a couple of times and now sell their own 36V mower. My mower was effectively a prototype when Bosch tried the 36V Bosch Professional range of garden equipment which all used their proprietary 36V 4.5Ah, 6Ah and 9Ah batteries. It never sold well and was discontinued very shortly after I bought it along with two of the 9Ah batteries.
New the mower cost around £1600 and the 9Ah batteries were £400 each. The mower uses two of the 36V 9Ah batteries in parallel for 36V and 18Ah capacity.
Last year I began to notice a deterioration in the battery capacity. I discovered the range was discontinued but found it had been sold to Honda who were producing their own tools using the exact same battery format. I bought two more 9Ah batteries for £300 each and resumed using the mower.
About a month ago the mower cut out during use but resumed correctly. I finished the cutting, washed under the deck and put it away.
The next time I went to use it, the mower would not start.
The "child proof safety key" is in place. This interrupts the main battery positive.
The blade spins freely and does not feel unusual.
===
FAULT DESCRIPTION
When holding the "start" button on the handlebars and holding the bar against the handle no power is sent to the motor. There is just a high pitched whine for a couple of seconds, a pair of faint clicks one second apart then nothing. The fault is consistent with either both batteries or just one battery in either slot.
===
Having opened the top case of the mower I can see all wiring connectors appear normal. Nothing appears out of place or burned. I can understand what most of the cables are for and have identified a few of the components. While there are red indicator LEDs on the two boards, all components are buried under black potting compound (of course). There are some test or programming pins protruding from the compound.
I have been following how the mower has been designed and can see the pair of parallel battery positives go to each side of the child-proof switch. Each side then goes to a pair of square components which I do not understand. I have not removed them to see if there are any markings on the other side. If they are fuses then I am confused as to why there are two of them running in series.
Because there are a pair of wires running from each battery direct to each potted board, the boards sense the batteries and power up, showing a steady red LED as soon as the safeties of child lock, side button and handle bar are set.
So, first question, does anyone recognise the symptoms and what are the two square modules I have highlighted in the second image please?
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