Davey D
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| posted on 15/7/08 at 09:05 AM |
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Electric Reverse
Ive come to the last bit of wiring now which is my electric Reverse using a modified starter motor.
The plan is to wire it via a relay which is triggered by the Gearbox Neutral light ( so that i can only reverse when the car is in neutral  )
What im wondering is what size fuse, and relay should i get that will handle the current draw from the motor?
Looking in the Durite Catalogue:
Standard relays take about 30A, Heavy duty around 70A, and Extra Heavy Duty take 100A
What should my choice be? Extra heavy duty relay, with a fuse around 60A ?
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Paul TigerB6
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| posted on 15/7/08 at 09:17 AM |
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Someone may correct me but i am sure you need a standard heavy duty battery cable for the main feed to the starter motor and then a switched feed to
the solenoid, so it wont be that high an ampage running through the relay - same as you would have through the ignition switch when turning the key.
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Mr Whippy
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| posted on 15/7/08 at 09:21 AM |
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Why not use an unmodified starter motor as they tend to come with the solenoid already attached
Fame is when your old car is plastered all over the internet
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BenB
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| posted on 15/7/08 at 09:21 AM |
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Starter motors consume huge amounts of electricty, especially during the first microseconds when they have to build up their magnetic field. If
you're pulsing the reverse button it'll continuously be doing this- big current!!
you have two options: go super high duty so it'll never go wrong or use a moderately high rated fuse, cable, relay etc etc and be prepared to
replace them with higher rated items as / when they burn out until you find the right combination 
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Howlor
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| posted on 15/7/08 at 09:23 AM |
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quote:
Originally posted by BenB
Starter motors consume huge amounts of electricty, especially during the first microseconds when they have to build up their magnetic field. If
you're pulsing the reverse button it'll continuously be doing this- big current!!
you have two options: go super high duty so it'll never go wrong or use a moderately high rated fuse, cable, relay etc etc and be prepared to
replace them with higher rated items as / when they burn out until you find the right combination
A selection of tea spoons in your pocket may be useful to put across the terminals!
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Mr Whippy
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| posted on 15/7/08 at 09:47 AM |
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quote:
Originally posted by Howlor
quote:
Originally posted by BenB
Starter motors consume huge amounts of electricty, especially during the first microseconds when they have to build up their magnetic field. If
you're pulsing the reverse button it'll continuously be doing this- big current!!
you have two options: go super high duty so it'll never go wrong or use a moderately high rated fuse, cable, relay etc etc and be prepared to
replace them with higher rated items as / when they burn out until you find the right combination
A selection of tea spoons in your pocket may be useful to put across the terminals!
I use to drive an old double decker that had to be started by sticking my house key across the starter motor terminals due to the starter switch not
working and the engine constantly stalling when cold, I’d get right funny looks from passengers
Fame is when your old car is plastered all over the internet
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Howlor
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| posted on 15/7/08 at 09:47 AM |
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nitram38
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| posted on 15/7/08 at 10:41 AM |
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You have two wires to your starter?
One is the main current from the battery and a smaller wire from your ignition key (start postion).
You either have a solenoid starter where the smaller wire goes or a seperate solenoid for the main current lead.
If you got it off a car, then go have a look at another one to find out!
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Davey D
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| posted on 15/7/08 at 11:07 AM |
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It is just the motor in a custom casing with a sliding gear that engages with a gear between the prop, and diff. It is From MNR.
It has just 1 terminal where you connect the +ve, and then it grounds through the casing where it bolts to the chassis.
I think ill just get some heavy gauge cable and the highest current rated relay i can get hold of, then a range of fuses to test, and stick with
lowest power one that doesnt go pop
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Howlor
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| posted on 15/7/08 at 12:31 PM |
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How about something like this?
Linky
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Davey D
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| posted on 15/7/08 at 01:07 PM |
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All i was basically asking was how much current will it draw when im reversing... not how to wire it up
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Fatgadget
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| posted on 15/7/08 at 01:25 PM |
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quote:
Originally posted by Howlor
How about something like this?
Linky
LOL. Cant get better than tried and tested old not to mention simple solutions to seemingly complicated problems.!
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Fatgadget
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| posted on 15/7/08 at 01:29 PM |
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quote:
Originally posted by Davey D
All i was basically asking was how much current will it draw when im reversing... not how to wire it up
How about asking MNR? Surely they must of tested it and compiled some relevant data before putting the product on the market ??
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Howlor
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| posted on 15/7/08 at 01:40 PM |
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Doing some quick research would suggest that you could draw 150A on initial start up dependent on what rating it is and the load upon it. This would
burn out the contacts on the 100A relay fairly quickly I would have thought.
Steve
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rf900rush
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| posted on 15/7/08 at 04:51 PM |
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Hi
The motor could pull 250amps + if loaded.
ie up a kerb/steep incline.
The Pre-engage soleniod will not change from no load to stalled.
If you are using your switch/relay to turn on the starter motor's pre-engage solenoid then a 30amp relay should be ok but 70amp will be
better.
Bigger = better, and 70amp car relays are not that much bigger.
If switching the motor directly then expect 250amp + for a car starter motor.
[Edited on 15/7/08 by rf900rush]
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