Using a 24V starter on a 12V system.

[Arnot]

OK, I spent this afternoon playing with my boat for a change and thinking about how best to use the original 24V starter on the 12V system I intend to install. Yes I know that a 24V system would make more sense but I want to be able to demonstrate 12V equipment to customers...

 

There is a reliable solution by using a Bosch relay made for just this purpose and fitted to Mercedes light commercials. The downside is that they are expensive and require quite complex heavy wiring which I wanted to avoid if possible.

 

So... It occured to me that a 24V series wound motor (a Bosch - CAV BS524 in this case) should deliver enough mechanical power to turn a three cylinder vintage diesel even on 12V as long as the solenoid was changed. In an attempt to prove this, I removed the back cover of the starter and with it connected to 12V, operated the solenoid contacts manually. The upshot was that the starter worked albeit a bit more slowly and the engine started with no problems.

 

What I can't decide or even find out is if this is a fluke based on my engine or if the older 24V CAV axial starters found on a lot of vintage engines will always behave this way. It's not a problem that comes up often but I have been asked about this sort of problem in the past and not been sure.

 

Anyone with any input here? Nibble? Tim?

 

Regards

 

Arnot

[soldthehouse]

I tried it on my Petter B4 and it didnt work! Maybe I didnt try hard enough but I didnt think 12v would turn a 24v starter. I just tried the wrong voltage before findng out I had a 24v starter, othewise I wouldnt even have assumed that 12v would do. I am heading for the same dilema soon so have an interest in the replies you get

[Sir Nibble]

Make your ming up, is this a bosch or cav? I am surprised the auxiliary coils worked at all! I've never done this nor heard of it done, why not get it lock torque tested on 12V and compare the results with the minimum spec for the engine.

[Arnot]

Make your ming up, is this a bosch or cav? I am surprised the auxiliary coils worked at all! I've never done this nor heard of it done, why not get it lock torque tested on 12V and compare the results with the minimum spec for the engine.

It's actually a genuine pre war Bosch CAV version on a pre war engine. I didn't know they existed until I bought it either... The fuel pump is also Bosch CAV. From the dreaded Wiki - In 1926 CAV was bought by Lucas. In 1931, CAV in partnership with Robert Bosch Ltd., became CAV-Bosch Ltd and began making fuel injection pumps for the diesel industry and later fuel systems for aircraft. Lucas bought Bosch's interest out in 1937 and it became CAV Ltd in 1939. The engine was made in 1937 so it must have been one of the last of these.

 

I was surprised the aux coils had enough waft as well but it managed about ten starts on the trot without a failure! Unfortunately the engine specs are now non existant (if for that matter they existed in the first place) so I can't go that route. As for torque testing I suspect it would be fairly crap but since the engine can be started by hand fairly easily it doesn't seem to need much.

 

The solenoid is a different mounting from the normal BS5 or Bosch version, the contacts seem to be the same as the early CAV ones but the mounting is by a single 6mm stud rather than the usual two machine screws. Since this version doesn't seem to be available anyway I am probably on a fools errand but I will have another look at the starter today and see if the modern version would fit without butchering the comm end bracket.

 

Regards

 

Arnot

[Sir Nibble]

I know the solenoid mounting you mean, same as a Simms SG. Given the history of the thing I would be inclined to sell the starter on, vintage, much sought after etc etc and buy a 12V starter. I can't think of anything that can be done to improve the 12V performance, that's a compound motor as you know and any jiggery pokery like reconnecting the series fields in shunt would be tantamount to sticking an iron bar across the battery terminals as well as screwing the performance characteristic. I would not rely upon a 24V starter on 12V. Apart from anything else, have you tried it on a cold frozen winter morning?

[Arnot]

I know the solenoid mounting you mean, same as a Simms SG. Given the history of the thing I would be inclined to sell the starter on, vintage, much sought after etc etc and buy a 12V starter. I can't think of anything that can be done to improve the 12V performance, that's a compound motor as you know and any jiggery pokery like reconnecting the series fields in shunt would be tantamount to sticking an iron bar across the battery terminals as well as screwing the performance characteristic. I would not rely upon a 24V starter on 12V. Apart from anything else, have you tried it on a cold frozen winter morning?

I think that the winter morning thing is the achilles heel of the scheme but can't be bothered to wait six months to try it . I did toy with tinkering with the windings just out of interest but it would probably be futile.

 

It seems a shame to ditch this starter; it's a bit of history in perfect condition and original to the engine. Anyway I will keep it in reserve for the moment and fit a BS5/12 I have lying about - keep it simple.

 

Thanks for your thoughts, I needed a bit of common sense to curb my enquiring mind!

 

Regards

 

Arnot

[Timleech]

Talking of tinkering with windings.......

I've been asked whether there could be any realistic mileage in converting two 110 Volt S7 starters to 24 Volt. These are anticlock starters, fairly rare and expensive beasts and there is some sort of a market for them in 24V but not in 110V. Allegedly.

I should think it unlikely unless you have a handy source of spare rotors, but what do I know? I'm not familiar with the inside of an S7, I expect the rotors are handed. Are they?

 

Tim

[frangar]

My JP has 24v starting but the rest of the boat is 12v.....I fitted 2x 85ah 12v starter batts which are charged from the 12v A127 alt via an Adverc Osca P 12v to 24v 10A Battery charger.....works really well.....when Im not replacing head gaskets!!...When I had the CAV starter rebuilt I did ask the guys that did it if it could be converted to 12v but the general consensus was that 24v would be much better on an engine the size of a JP...

 

Edited to add that mine is a BS5 as well. These guys:

 

http://www.broadwayelectrical.co.uk/classi...ar_repairs.html

 

did an ace job of reconditioning it...were very knowledgeable about old CAV starters and had spares etc....might be worth a call

 

 

 

HTH

 

Gareth

Edited July 18, 2010 by frangar

[Sir Nibble]

Talking of tinkering with windings.......

I've been asked whether there could be any realistic mileage in converting two 110 Volt S7 starters to 24 Volt. These are anticlock starters, fairly rare and expensive beasts and there is some sort of a market for them in 24V but not in 110V. Allegedly.

I should think it unlikely unless you have a handy source of spare rotors, but what do I know? I'm not familiar with the inside of an S7, I expect the rotors are handed. Are they?

 

Tim

Never heard of a 110V starter. Never heard of an S7 either. These are starter motors aren't they, rather than motor starters?

[Timleech]

Never heard of a 110V starter. Never heard of an S7 either. These are starter motors aren't they, rather than motor starters?

 

CAV starter the next size up from a BS6, they (at least the ones I've seen) have an external solenoid box with solenoids looking very much like those on the end of a BS5/6.

 

Tim

Edited July 18, 2010 by Timleech

[Arnot]

CAV starter the next size up from a BS6, they (at least the ones I've seen) have an external solenoid box with solenoids looking very much like those on the end of a BS5/6.

 

Tim

Our local scrappy just bought about 200 scrap tank engines from the MOD and when I was last there had a load of the starter hanging about. I doubt they could be used as they were but they may well harvest useful spare parts such as armatures, solenoids and field windings. I can go and see if he still has them and what they are if this helps.

 

Regards

 

Arnot

 

CAV starter the next size up from a BS6, they (at least the ones I've seen) have an external solenoid box with solenoids looking very much like those on the end of a BS5/6.

 

Tim

I am intigued here, what size of narrow boat are these fitted to? I seem to remember working on one from a big Paxman but thought it was an SP7, it had to be nearly 40 years ago though...

 

Regards

 

Arnot

[Timleech]

Our local scrappy just bought about 200 scrap tank engines from the MOD and when I was last there had a load of the starter hanging about. I doubt they could be used as they were but they may well harvest useful spare parts such as armatures, solenoids and field windings. I can go and see if he still has them and what they are if this helps.

 

Regards

 

Arnot

 

 

I am intigued here, what size of narrow boat are these fitted to? I seem to remember working on one from a big Paxman but thought it was an SP7, it had to be nearly 40 years ago though...

 

Regards

 

Arnot

 

No connection with narrow boats, sorry.

Used on Paxmans and Mirrlees Blackstones, among other engines.

 

Tim

 

 

Our local scrappy just bought about 200 scrap tank engines from the MOD and when I was last there had a load of the starter hanging about. I doubt they could be used as they were but they may well harvest useful spare parts such as armatures, solenoids and field windings. I can go and see if he still has them and what they are if this helps.

 

Regards

 

Arnot

 

 

Thankyou, it would be appreciated.

 

Tim

[pearley]

Got nothing to do with this thread but I once had a Daf 33 pickup with a 6V system and regularly slaved started it with a 12V battery.

 

Pete

[WotEver]

Got nothing to do with this thread but I once had a Daf 33 pickup with a 6V system and regularly slaved started it with a 12V battery.

 

Pete

That'd put a nice charge into the 6V batts then

 

Tony

[Arnot]

No connection with narrow boats, sorry.

Used on Paxmans and Mirrlees Blackstones, among other engines.

 

Thankyou, it would be appreciated.

 

Tim

I went and had a look but they are marked K60 although this might be the engine type since they were from APC's originally. They seemed to be a rather longer than normal version of the CAV Axial starter and were about 6" in diameter but I couldn't get close enough to measure them. They also had a very sophisticated silver plated connection system and probably cost the MOD abut £50k originally.

 

Regards

 

Arnot

[Timleech]

I went and had a look but they are marked K60 although this might be the engine type since they were from APC's originally. They seemed to be a rather longer than normal version of the CAV Axial starter and were about 6" in diameter but I couldn't get close enough to measure them. They also had a very sophisticated silver plated connection system and probably cost the MOD abut £50k originally.

 

Regards

 

Arnot

 

 

Thanks for that. I'm not sure that the S7 is actually 7" in diameter, may be nearer to 6" but don't quote me as I haven't handled one for a while, and it doesn't have the contactor housing like the BS 5 & 6.

 

Tim

[Sir Nibble]

I went and had a look but they are marked K60 although this might be the engine type since they were from APC's originally. They seemed to be a rather longer than normal version of the CAV Axial starter and were about 6" in diameter but I couldn't get close enough to measure them. They also had a very sophisticated silver plated connection system and probably cost the MOD abut £50k originally.

 

Regards

 

Arnot

I don't remember the designation of the machine but if this is the slightly longer but-otherwise-identical to a BS6/U6, then they were fitted to the chieftain MBT. Those connections are called Southdown connectors, snazzy huh. The chieftain engine was the L60 maybe you're misreading that?

[Arnot]

I don't remember the designation of the machine but if this is the slightly longer but-otherwise-identical to a BS6/U6, then they were fitted to the chieftain MBT. Those connections are called Southdown connectors, snazzy huh. The chieftain engine was the L60 maybe you're misreading that?

Possibly but possibly not, the APC (FV432) had the K60 engine fitted, it was a baby version of the Chieftain's L60 and even more unreliable... I really remember the FV434 which was the REME version with the jib and platform at the back. The jib was intended for the removal of power packs but doubled as an apple harvester when fitted with a bit of camo netting.

 

Anyway there seem to be about ten of them lying about in various states of damage. If you know anyone who could use them at more or less scrap value, let me know quickly, they are going to be melted down shortly.

 

Thinking about it it did seem reminiscent of the U6.

 

Regards

 

Arnot

[Mark Tee]

This is a very late reply to a very old post - but if someone was reading through for information in the future, this may be of use:-

A starter motor designed for 24V will (off-load) run fairly happily BUT as others have pointed out, UNDER load is where the real difference happens and the main sticking point is that a starter motor will (roughly) reduce in power by FOUR times if the supply voltage is halved. This is because as the voltage decreases, less current can flow (I = V/R) so if (for example) you have a 24V starter motor which is rated at 2KW when powered from 24V, it will only have (at best) 500W and NOT 1KW when powered from 12V

If the engine is quite small (and ideally petrol and not mid winter), then a 24V starter might be able to crank with enough power to start on 12V but it may also cause the motor to "stall" not having enough power to crank the engine - but pulling enough power to start overheating in a stalled condition. Really bad for the motor.

I'm afraid, unless you have a VERY powerful starter motor on a fairly small engine, reducing the voltage to 12v is likely to end up with unreliability and potentially damage due to the motor's stator from high "stall current".

I do appreciate the OP managed to make this work (impressive), but this is really not a system I would want to recommend to ANYONE - far less potential customer or people that need a RELIABLE starting system. If you can "get someone going" in an emergency like this - awesome - but as for a reliable option, I'm afraid it isn't.