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Low voltage on leisure batteries while running alternator?


Tasemu

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Just now, Mike the Boilerman said:

 

No, that IS the light we are all asking about! What happens to it when you start the engine? Exactly?

 

Cheers mike! When i put the key in the light goes red, when i start the engine the light stays red. When i switch the key to the off position the light will go out, however the engine will still run normally.

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9 minutes ago, Tasemu said:

I got a clamp meter coming tomorrow from amazon and a spare starter battery in the boat which i'll try tonight. What voltage should my spare starter battery be at while the engine is running if I were to switch them out. Should it jump to 14v right away?

 

You have a spare starter battery in addition to the one wired in?

 

Is it new or obviously old and used? What voltage is it at now, not connected?

 

The alternator will normally be putting out 14.4v into reasonably well charged batteries. If a battery is heavily discharged it will drag the alternator output votage down to typically 12-13v or so while it sucks in a high charge current, this is why a clamp meter is essential - to measure the charge current.

 

3 minutes ago, Tasemu said:

Cheers mike! When i put the key in the light goes red, when i start the engine the light stays red. When i switch the key to the off position the light will go out, however the engine will still run normally.

 

Ah right. It should go out. Does it stay ON even if you rev the nuts off the engine? (Technical term.)

 

 

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18 minutes ago, Tasemu said:

Cheers mike! When i put the key in the light goes red, when i start the engine the light stays red. When i switch the key to the off position the light will go out, however the engine will still run normally

It's not a good idea to run the engine with the "ignition" turned off. This can kill the alternator. How often have you done this?

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4 minutes ago, philjw said:

It's not a good idea to run the engine with the "ignition" turned off. This can kill the alternator. How often have you done this?

 

I don't think there is any risk in doing this. It is only the 'excite' current being disconnected. It is disconnection of the main alternator output whilst running that busts them. 

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24 minutes ago, Mike the Boilerman said:

 

You have a spare starter battery in addition to the one wired in?

 

Is it new or obviously old and used? What voltage is it at now, not connected?

 

The alternator will normally be putting out 14.4v into reasonably well charged batteries. If a battery is heavily discharged it will drag the alternator output votage down to typically 12-13v or so while it sucks in a high charge current, this is why a clamp meter is essential - to measure the charge current.

 

 

Ah right. It should go out. Does it stay ON even if you rev the nuts off the engine? (Technical term.)

 

 

- Yep i have a spare starter in addition to the one wired in currently. It looks in good condition, i will measure the voltage when I get home from work and report back.

- Could my current starter battery be discharged, and i just need to wait for the alternator to to finish the high-current charge?

- The light has always been on when the key in turned to the on position from what I have seen, i will have a go at revving the nuts off it when I get home (before swapping out for the new starter battery) and report back with details.

7 minutes ago, philjw said:

It's not a good idea to run the engine with the "ignition" turned off. This can kill the alternator. How often have you done this?

Only once.

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Just now, Tasemu said:

- Could my current starter battery be discharged, and i just need to wait for the alternator to to finish the high-current charge?

 

 

Almost certainly not. The red light staying ON tells us either the alternator is not charging or there is a wiring error. The latter is highly unlikely as presumably it all used to work correctly. 

 

 

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Just now, Mike the Boilerman said:

 

Almost certainly not. The red light staying ON tells us either the alternator is not charging or there is a wiring error. The latter is highly unlikely as presumably it all used to work correctly. 

 

 

It is possible, as the voltage sensitive split charge relay was only installed right before I moved onto the boat.

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43 minutes ago, Tasemu said:

I got a clamp meter coming tomorrow from amazon and a spare starter battery in the boat which i'll try tonight. What voltage should my spare starter battery be at while the engine is running if I were to switch them out. Should it jump to 14v right away?

You did check to see that the meter can measure DC amps I hope?  Quite a few models just do AC I believe. 

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28 minutes ago, philjw said:

It's not a good idea to run the engine with the "ignition" turned off. This can kill the alternator. How often have you done this?

No it can't, even if the alternator self energises.

 

This is a very common misconception I think based on a partial understanding of the fact that when the LOAD is disconnected from a  running alternator there is a fair chance the resultant voltage surge may be high enough to damage components.

 

Running an alternator with the ignition turned off will result in one of the following:

 

The alternator self energising but as the   load is till connected there is no problem.

The alternator not energising because there is no warning lamp current to allow it so still safe.

Turning the ignition off while running - the current from the field diodes will keep the alternator energised so still safe. Even if the rotor field did collapse there would still be a load connected to absorb the results pulse but such an outcome is not very likely.

 

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21 minutes ago, Tasemu said:

It is possible, as the voltage sensitive split charge relay was only installed right before I moved onto the boat.

 

Forget that for now, the  fact the warning lamp stays on implicates the alternator.

 

Turn on the ignition but do not start the engine

Locate the D+ (warning lamp terminal) on the alternator.

Disconnect the D+ wire and the lamp should go out, if it stays on there is a wiring fault, possibly a short to metal between the bulb and alternator OR it is not a charge warning lamp, possibly oil pressure, glow plug warning (miswired) or overheat.

If the bulb goes out then touch the connection on the end of the cable to some clean metal, the bulb should come on. I am confident it will.

Refit the D+ cable.

 

If that tests out OK then the alternator should excite, perhaps with a bit of a rev. If it does not it implies an alternator fault so the easiest way to prove it is to take it off and get it tested.

 

Until you get that warning lamp going off when you   start and rev the engine there is every possibility there is no charge for the VSR to deal with. The VSR will need between 13.4 and 13.8 volts to operate, usually around 13.6V

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20 minutes ago, Tasemu said:

Just noticed it is only AC current measure... Managed to cancel the order. ?

 

DC clamp meters are hard to find. AC clamp meter descriptions often mislead you into expecting DC current by stating clearly how they measure DC voltage. The only DC current clamp on the market at a sensible price that I know of is the UNI-T UT210E. Google it. Usually about £40.

 

 

Strongly recommend buying one, you'll find endless uses for it. 

 

 

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15 minutes ago, Mike the Boilerman said:

 

DC clamp meters are hard to find. AC clamp meter descriptions often mislead you into expecting DC current by stating clearly how they measure DC voltage. The only DC current clamp on the market at a sensible price that I know of is the UNI-T UT210E. Google it. Usually about £40.

 

 

Strongly recommend buying one, you'll find endless uses for it. 

 

 

https://www.amazon.co.uk/UT210E-Current-Meters-Capacitance-Tester/dp/B00O1Q2HOQ/ref=sr_1_1_sspa?keywords=UNI-T+UT210E&qid=1559215298&s=gateway&sr=8-1-spons&psc=1

 

This one? I'll definitely pick it up if so. :)

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27 minutes ago, Tony Brooks said:

 

Forget that for now, the  fact the warning lamp stays on implicates the alternator.

 

Turn on the ignition but do not start the engine

Locate the D+ (warning lamp terminal) on the alternator.

Disconnect the D+ wire and the lamp should go out, if it stays on there is a wiring fault, possibly a short to metal between the bulb and alternator OR it is not a charge warning lamp, possibly oil pressure, glow plug warning (miswired) or overheat.

If the bulb goes out then touch the connection on the end of the cable to some clean metal, the bulb should come on. I am confident it will.

Refit the D+ cable.

 

If that tests out OK then the alternator should excite, perhaps with a bit of a rev. If it does not it implies an alternator fault so the easiest way to prove it is to take it off and get it tested.

 

Until you get that warning lamp going off when you   start and rev the engine there is every possibility there is no charge for the VSR to deal with. The VSR will need between 13.4 and 13.8 volts to operate, usually around 13.6V

Will do, cheers!

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3 hours ago, Mike the Boilerman said:

 

DC clamp meters are hard to find. AC clamp meter descriptions often mislead you into expecting DC current by stating clearly how they measure DC voltage. The only DC current clamp on the market at a sensible price that I know of is the UNI-T UT210E. Google it. Usually about £40.

 

 

Strongly recommend buying one, you'll find endless uses for it. 

 

 

There is certainly also a Unitrend UT203 model that does DC amps. (I know this as I have just been using mine in that mode).

Probably a similar price, but it could be worth comparing capabilities of each, and prices, before you order.

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23 minutes ago, alan_fincher said:

There is certainly also a Unitrend UT203 model that does DC amps. (I know this as I have just been using mine in that mode).

Probably a similar price, but it could be worth comparing capabilities of each, and prices, before you order.

 

Ah good to see that back on the market. A much better instrument I thought it was superseded by the 210E.

 

When I bought my three 210Es(!) I couldn't find a 203 for love nor money, only 210Es. Now there are loads on ebay at about £33.

 

 

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Finally back, i'm going to run the alternator tonight and make sure that the light is on, then run these tests you have all recommended. Had to go away for the weekend.

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7 hours ago, Tasemu said:

Finally back, i'm going to run the alternator tonight and make sure that the light is on, then run these tests you have all recommended. Had to go away for the weekend.

Yup. Just follow post #37 carefully and methodically. Then report back :)

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