CAV BS5 starter motor - current draw

[agg221]

Having now established that the issue with our starter motor was that it is a 24V starter rather than 12V, I now need to make some changes.

 

The options appear to be to fit a second starter battery or to fit a 12V starter motor. My preference is for the latter as I would rather avoid the complexity on the electrical side, and I have a very restricted space for starter batteries and would rather not try to find a model which fits two in.

 

I do have a 12V CAV BS5 starter motor which is untested but either should work or could be reconditioned.

 

The question is therefore over the wiring. In theory, this starter motor can draw 930A, and I have a 900CCA battery. However, looking at the cable dimensions required this seems extreme. In reality I don't think the engine is capable of taking anything like that current to turn it (that equates to 15hp, which is nearly as much as the engine!) so I need some practical experience from people with similar sized engines about starter cable cross-section. The same starter motor is used on the Lister JP2, the Kelvin J and K and various Gardners to my knowledge, so it would be useful to know what size cable others have fitted.

 

Thanks

 

Alec

[nicknorman]

No direct experience but to be clear, you don’t need cable rated at 930A. Cable rating is for continuous operation and related to heat build up. The rest of the setup (starter motor and battery) is not rated for continuous operation. Probably the start motor is rated for 15seconds continuous or maybe 30 seconds. Also the current drawn is inversely proportional to the rpm so the 930A will only happen with the motor stalled and still being fed by 12v, which is not going to happen!

 

More important is voltage drop so the cable x-section relates in part to the distance from the battery to the motor (and not forgetting the negative return of course!). Top of my head I’d say 70mm^2 would be more than adequate, 50mm^2 would be adequate if the distances are not too long. But there is no exact right answer because it depends on how much voltage drop you and the starter are prepared to tolerate.

[agg221]

5 minutes ago, nicknorman said:

No direct experience but to be clear, you don’t need cable rated at 930A. Cable rating is for continuous operation and related to heat build up. The rest of the setup (starter motor and battery) is not rated for continuous operation. Probably the start motor is rated for 15seconds continuous or maybe 30 seconds. Also the current drawn is inversely proportional to the rpm so the 930A will only happen with the motor stalled and still being fed by 12v, which is not going to happen!

 

More important is voltage drop so the cable x-section relates in part to the distance from the battery to the motor (and not forgetting the negative return of course!). Top of my head I’d say 70mm^2 would be more than adequate, 50mm^2 would be adequate if the distances are not too long. But there is no exact right answer because it depends on how much voltage drop you and the starter are prepared to tolerate.

Thanks - 50-70mm is where I have been guessing. Cable run is about 1.5m by the time is has fed through the relay. If the engine is sufficiently seized that I am feeding full current into the motor then I have bigger problems!

 

Alec

[David Mack]

I too will soon be wiring up a similar starter motor. And my related question is what size cable do I need for the starter solenoid?

[john.k]

The Gardner 4LW in my crane only had one 12v battery of the size commonly used in 4x4s,and started easily at any time .....although it doesnt get below about 8deg C here............the BS5 is a very efficient starter .

[BEngo]

5 hours ago, David Mack said:

I too will soon be wiring up a similar starter motor. And my related question is what size cable do I need for the starter solenoid?

My BS 5 is operating quite happily on a solenoid operating cable of 2.5 sq mm and Nyvin  00  ( about 50 sq mm)  power cables.   The solenoid run is about 2m and the power run about 1.5 m total.

 

N

 

[agg221]

57 minutes ago, BEngo said:

My BS 5 is operating quite happily on a solenoid operating cable of 2.5 sq mm and Nyvin  00  ( about 50 sq mm)  power cables.   The solenoid run is about 2m and the power run about 1.5 m total.

 

N

 

Thanks - that's exactly the information I needed. It also ties in with previous thoughts above.

 

Alec

[john.k]

One thing to keep in mind is if your starter has a steel pinion ,it s for  a hardened ring gear ......bronze pinion is for a soft ring gear,which is what most old motors will have.

[agg221]

17 hours ago, john.k said:

One thing to keep in mind is if your starter has a steel pinion ,it s for  a hardened ring gear ......bronze pinion is for a soft ring gear,which is what most old motors will have.

I'm OK in that regard. I have a couple of spare bronze pinions, one NOS from a company in Manchester and the other advertised on Facebook for a Gardner U6 starter motor but conveniently they are the same part. I haven't worked out how to take it apart and change the pinion yet though, that joy is yet to come...

 

Alec

[BEngo]

Remove the split  pin and the castellated nut and it comes off.

 

Replacement is the reverse of removal.  You do need to check he clearance from pinion to flywheel  remains correct if you have changed the pinion with the motor still on the engine.

 

I have a BS5  workshop manual somewhere.

 

N

[agg221]

12 hours ago, BEngo said:

Remove the split  pin and the castellated nut and it comes off.

 

Replacement is the reverse of removal.  You do need to check he clearance from pinion to flywheel  remains correct if you have changed the pinion with the motor still on the engine.

 

I have a BS5  workshop manual somewhere.

 

N

Thanks - that sounds a lot easier than I had feared. I was anticipating springs buried in there...

 

It will be a replacement starter motor anyway, changing from 24V to 12V, so I will have to set up the clearance regardless. To be honest, when I re-fitted the motor which is currently on I eyeballed it and it has worked fine. I could take a more structured approach and use a drill bit this time.

 

Alec

[Split Pin]

 

A picture makes it easier to explain. Best to stand the starter upright so that the clutch plates remain in position. 

The pinion should be 1/8 inch away from the ring gear when set correctly

Edited October 31, 2023 by Split Pin

[agg221]

6 hours ago, Split Pin said:

 

A picture makes it easier to explain. Best to stand the starter upright so that the clutch plates remain in position. 

The pinion should be 1/8 inch away from the ring gear when set correctly

Thanks for that - the picture certainly helps, and it doesn't have any problematic springs to go flying across the workshop! Just to clarify on the first picture, is there any relevance to parts 54 and 55 being shown? E.g. do they need to be removed prior to starting to remove the split pin and nut?

 

Thanks

 

Alec

[jonesthenuke]

This is from the Gardner LW engine manual and gives cable sizes (in imperial units). I have measured the starting current of our 3LW with 12 V starter. IIRC it was 300-400 A

 

ELECTRICAL EQUIPMENT
Voltage.-24 volt (min.) equipment is recommended for all vertical and horizontal LW Type engines.
 Battery.--The size of battery wil usually be determined by lamp load, but for engine starting only the recommended capacity is 100 ampere-hours at 10-hour rate.
 Cable Sizes. The minimum sizes of cable should be not less than thefollowing:-
Battery to Starter 61/044in. 10ft.(3,048mm.)max.

Alternator to Control Board 226/-012in.5ft. (4,572mm.)max.

Field Switch to starter. 14/-012in.
Control Board to Battery 266/-012 in.
 

[john.k]

I think these starters have two leads to the starter ,so they can be used on insulated return systems that many old trucks had ............anyway ,two leads solves a lot of the problems people have with poor earthing affecting starter performance.

[jonesthenuke]

2 hours ago, john.k said:

I think these starters have two leads to the starter ,so they can be used on insulated return systems that many old trucks had ............anyway ,two leads solves a lot of the problems people have with poor earthing affecting starter performance.

Yes they do.

 

[Split Pin]

2 hours ago, john.k said:

I think these starters have two leads to the starter ,so they can be used on insulated return systems that many old trucks had ............anyway ,two leads solves a lot of the problems people have with poor earthing affecting starter performance.

They are manufactured with both insulated return and case return, and they both have the two terminals.

10 hours ago, agg221 said:

Thanks for that - the picture certainly helps, and it doesn't have any problematic springs to go flying across the workshop! Just to clarify on the first picture, is there any relevance to parts 54 and 55 being shown? E.g. do they need to be removed prior to starting to remove the split pin and nut?

 

Thanks

 

Alec

i have dismantled a number of these units an have never encountered those items, but if they are there then I would suggest that they need to be removed before removing the pinion. The illustration is from a book published in the early 1950's so may be applicable to units manufactured in the 1940's. Another couple of pictures that may help

[BEngo]

To me, item 55 in Split Pin's previous post looks like the oiler screw.  Item 55 is the felt pad and stuff that holds the oil.  

Last time I had a pinion off there was no need to remove them, but it does seem like a good idea.

 

N

[Split Pin]

1 hour ago, BEngo said:

To me, item 55 in Split Pin's previous post looks like the oiler screw.  Item 55 is the felt pad and stuff that holds the oil.  

Last time I had a pinion off there was no need to remove them, but it does seem like a good idea.

 

N

I would agree that it looks like a spring and oil pad but there is an oil cup shown behind it. Non of the ones that I have dismantled have had a spring just a short screw to allow oil to added, so it can possibly be ignored. I have dug out the book from which the picture was taken and there is no mention of the need to remove the items. Text from the book.

 

Edited November 1, 2023 by Split Pin

[jonesthenuke]

From CAV manual 2571/2

 

[agg221]

Thanks everyone!

 

Replacing the pinion is a job for the weekend (assuming the floodwaters aren’t blocking the path to the shed). I will let you know how it goes.

 

 The main reason this information is so useful is to confirm that there is nothing lurking in there like a compression spring or retaining grub screw which can cause no end of problems if you don’t know about it in advance.

 

Alec

[agg221]

I found an online copy of the starter motor installation specification for Kelvins. It isn't part of the normal manual - it is part of the specific electrical equipment manual. It includes wire dimensions - not quite sure how to interpret the numbers but if the second part is a cross-section in square inches and the two options are for 24V and 12V then it would make sense that the larger dimension is for a 12V system. If so, 0.064 square inches is 41mm2, which seems reasonable.

 

Alec

 

 

[David Mack]

26 minutes ago, agg221 said:

If so, 0.064 square inches is 41mm2, which seems reasonable.

I think 19/0.064" refers to a wire with 19 strands each of 0.064" diameter, which comes to near enough 50 mm squared.

61/0.036" equates to 51 mm squared.

 

[agg221]

11 minutes ago, David Mack said:

I think 19/0.064" refers to a wire with 19 strands each of 0.064" diameter, which comes to near enough 50 mm squared.

61/0.036" equates to 51 mm squared.

 

That would make sense - it also gives the correct specification for wiring up your solenoid!

 

Alec

[BEngo]

2 hours ago, agg221 said:

I found an online copy of the starter motor installation specification for Kelvins. It isn't part of the normal manual - it is part of the specific electrical equipment manual. It includes wire dimensions - not quite sure how to interpret the numbers but if the second part is a cross-section in square inches and the two options are for 24V and 12V then it would make sense that the larger dimension is for a 12V system. If so, 0.064 square inches is 41mm2, which seems reasonable.

 

Alec

 

 

 

Could I have a link to the electrical equipment manual please?  Google does not find it for me.

 

N