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BMC 1.5 Starter motor wiring


colinnorth

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I have just had an issue with my starter motor failing (as deduced by RCR).

Having replaced the starter motor I am not sure that was the issue.

Normally when starting the voltage as indicated on my panel (analogue meters) drops to about 10.5V whilst cranking. With the issue (for which I called RCR) I noticed that the cranking volts seemed to drop lower - about 8-9v. This meant the starter motor failed to turn the engine over correctly and made an 'orrible noise. RCR checked my batteries with a drop tester and deemed them OK.

Whilst re-connecting the new starter motor I traced the wiring back and found that the main 12V feed to starter motor came from the rotor of the OFF/1/BOTH/2 switch. This made me wonder if a higher resistance in the OFF/1/BOTH/2 switch was causing the problem.

I have now wired the starter motor directly back to the starter battery (as it would have been on a car).

Question - is that now correctly wired? It does mean that I have to remove the starter battery + lead to isolate the engine for working (as one would with a car)?

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1 hour ago, colinnorth said:

I have just had an issue with my starter motor failing (as deduced by RCR).

Having replaced the starter motor I am not sure that was the issue.

Normally when starting the voltage as indicated on my panel (analogue meters) drops to about 10.5V whilst cranking. With the issue (for which I called RCR) I noticed that the cranking volts seemed to drop lower - about 8-9v. This meant the starter motor failed to turn the engine over correctly and made an 'orrible noise. RCR checked my batteries with a drop tester and deemed them OK.

Whilst re-connecting the new starter motor I traced the wiring back and found that the main 12V feed to starter motor came from the rotor of the OFF/1/BOTH/2 switch. This made me wonder if a higher resistance in the OFF/1/BOTH/2 switch was causing the problem.

I have now wired the starter motor directly back to the starter battery (as it would have been on a car).

Question - is that now correctly wired? It does mean that I have to remove the starter battery + lead to isolate the engine for working (as one would with a car)?

The BSS requires ALL electrical circuits bar a very few special cases to be isolated by a master switch so if your 1,2 both, off switch is also the master switch then as far as the BSS is concerned it was correct and now you risk a failure. Having had a couple apart  I  fail to understand how those switches can hope to cope with starter current or large inverter currents come to that. I suspect the wipers and tracks in your switch are in a very sorry way. My advice is before your next BSS change the whole thing to  ordinary good quality master switches and a VSR to split the charge. Its not too difficult and its important to  taker the main alternator feed to the DOMESTIC bank.

 

 

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1 hour ago, colinnorth said:

Tony,

Thank you for your prompt reply. I will attend to this matter as soon as I can rather than wait for the next BSS. I will hunt down a good Master Switch

That will be OK if you put it in the main starter lead but other services draw electricity thorough your big switch that seems to be failing. If you want to do away with the big switch you will need two master switches for best practice (one engine and one domestic) plus something to split the charge which is what a VSR will do.

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On 28/11/2019 at 17:25, colinnorth said:

Tony,

Thank you for your prompt reply. I will attend to this matter as soon as I can rather than wait for the next BSS. I will hunt down a good Master Switch

Look at Blue Sea switch’s. Not the cheapest but probably the best you can get....steer clear of the Chinese stuff on eBay. 

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