Starter motor wiring modification

[kentishvanman]

Hi,
Does anyone know where (on here) the diagram for the starter motor wiring mod is?
I think it shows a 30amp relay but can't remember wiring size/route etc.
Don

[CovKid]

I just had a hunt too and unless its in the WIKI now, its probably vanished in the last forum shrink.

Lets see if we can work backwards and recreate it for you. Is your battery up front or in the rear and why did you need a relay?

I've actually got a Bosch starter in front of me right now as I'm soldering in a new set of brushes.

[bigherb]

There you go Don


I usually mount them hear so you can pull the red/black wire through

[ghost123uk]

I take it this is to take the load off the ignition key switch.

[bigherb]

Yes it takes 32A to pull in the solenoid and 11A to hold in, importantly it stops the back EMF arcing across the key contacts when the key is released.

[ghost123uk]

Actually I knew that I wrote what I did to assist anyone else reading the post Mind you, I did not know the figures = 32A and 11A plus the back emf (xxxxV) on release, from the solenoid coil Flip, so a relay is a good idea then.

[CovKid]

Yep. I'm about to rewire my complete alternator/battery/starter cable network. Much of it is badly corroded now matter how far I chop it back and crappy terminals throughout. Seems prudent time (now weather is improving) to rethink it all and reduce any voltage drops.

I'm assuming then, that the relay pictured is at least 45amps. The only slight downside I suppose is it means more contacts to corrode and play up, but its definately an improvement otherwise. Not so sure about reducing that down to a small spade terminal - I think I'd be looking for a more industrial relay with much bigger terminals than that. Eyelets ideally - if only for longevity.

Something like http://www.ebay.co.uk/itm/Relay-100A-12 ... 3cd8cd1a8c" onclick="window.open(this.href);return false; - probably overkill though considering its not carrying THAT much current but terminals look better.

[bigherb]

I just use a standard 40A relay, no need to go OTT it is only intermittent use.

Just spray the connectors with silicone grease to protect them I like the Servisol one it is a nice consistency.

http://www.ebay.co.uk/itm/SERVISOL-200m ... 2c838698e7" onclick="window.open(this.href);return false;

[clinning]

Sounds very technical all this, can some some explain this as if I was a 5 year old? Benefits/worth doing?

[CovKid]

Yes, good stuff that. I also use an automotive black sealing putty as its very mouldable and totally waterproof. As long as it keeps the air and water from furring up connections it'll do the job. Keeping it in the engine bay is best place for it - beats having it underneath thats for sure.

Benefits? Less strain on your ignition contacts (at steering wheel) as its only supplies a very tiny current instead, the relay taking all the brunt.

[clinning]

All this strain on the contacts then, this mean that will break or what? Is this mod something that you would say should be done?

[bigherb]

Sounds very technical all this, can some some explain this as if I was a 5 year old? Benefits/worth doing?

These vans where built for a nominal 10 year life the youngest ones are now approaching 22 years old. In that time the wiring and connections start to oxidise causing voltage drop. One of the symptoms is the hot start problem where the starter will not operate when the engine is hot.
When the key is turned the current flow goes through the ignition switch down the signal cable to the starter solenoid it passes through the solenoid to the starter motor brushes to turn the starter motor slowly to mesh the gears then to earth. Any dirt on the starter brushes/commutator causes resistance (the hotter it is the more resistance) impeding the flow back to earth. With voltage drop down the signal wire the voltage is not able to punch through the high resistance in the starter motor, the relay eliminates the voltage drop by bypassing a large chunk of the wiring for the heavy part of the current flow and gives full battery voltage to punch through the high resistance.
The other problem is when you switch off an electro magnet it induces a high voltage back up the signal cable and tries to jump across the gap as the key is released, slowly eroding the contacts causing the switch having to be turned further to energise the starter until it only works when the key hits the stop, then finally not working at all. Modern cars have to be protected if the vehicle ECU's need a cranking signal from the high voltage and are fitted with a relay or in F0rds case a cheaper blocking diode.

[clinning]

Epic reply cheers mate

[CovKid]

That explanation sends mixed messages though. After all, that relay circuit only energises the solenoid on the starter (yet another relay) so its one relay switching another relay (for simple explanation). Its the big thick red cable that does all the work when it comes to cranking.

My main starter cable is very corroded now and bits of wire gradually breaking away from the terminals. Another forum member gave me 4 metres of cable today to replace it with, plus terminals. Its my job for tomorrow.

For most people the solenoid works fine on the existing wiring (look how long Beetles have been going with that setup) and in all likelihood they'll get years of trouble-free service other than the usual starter motor breakdowns. To really make a difference, the condition of all the heavy cables underneath need to be taken into account too since in the end, its all only as good as the weakest link.

Modern cars have relays for almost everything, which is why the looms are so complicated. Sometimes simple works best, it all depends on what floats your boat. Put it this way, I'd put condition of existing cables ahead of fitting a relay. The relay is a nice touch but its essential to have good solid connections between alternator, starter and battery to start with. Sadly, most that I've seen in recent years have very poor cables - they just get forgotten about. I've lost coulnt of how many I've seen with bare wire twisted around posts, squeezed between two washers and a nut slapped on top.

[bigherb]

After all, that relay circuit only energises the solenoid on the starter (yet another relay) so its one relay switching another relay (for simple explanation).

No the starter has to rotate slowly first to mesh to teeth before the main solenoid contacts close and turn the engine over, otherwise if two teeth are aligned they would just hit each other and not engage.

For most people the solenoid works fine on the existing wiring (look how long Beetles have been going with that setup) shock:

It was an authorised VW modification for Beetles particularly 6V ones.