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Helping someone out with a new alternator. The engine is a Lister of some sort. The alternator is not charging. No change in battery voltage and the alternator warning light is not going out. The back of the alternator is shown below. The blue wire goes to the warning light, then to ignition switched Aux position +ve. There is no tacho on this boat, so W is unconnected. The alternator to battery connection goes to B+. Beside the B+ stud there is another blade connection, partly recessed, that is also at battery voltage. What is this? Is it for a battery sense wire? Should this connect to the battery? Will this solve the problem?

Jennyalt-lp.jpg.86b71e52b82355ffb6222492c8d58207.jpg

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Thanks @MoominPapa that is useful to know. Will see if the owner complains about not being able to listen to the radio. It has turned out I wasn't giving the engine enough beans to start it charging. A bit more throttle and the warning lamp went out. Oh well.

Jenny

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26 minutes ago, Jen-in-Wellies said:

It has turned out I wasn't giving the engine enough beans to start it charging. A bit more throttle and the warning lamp went out. Oh well.

Warning lamp is the wrong size, a resistor in parallel with the lamp will cure this problem.

Or of course the correct size lamp but often the resistor is easier to fit😉

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1 minute ago, Loddon said:

Warning lamp is the wrong size, a resistor in parallel with the lamp will cure this problem.

Or of course the correct size lamp but often the resistor is easier to fit😉

May have a suitable high power low resistance ceramic resistor in the bits box somewhere. Will give it a try if it is there. The lamp is a standard old fashioned car warning light.

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14 minutes ago, Jen-in-Wellies said:

May have a suitable high power low resistance ceramic resistor in the bits box somewhere. Will give it a try if it is there. The lamp is a standard old fashioned car warning light.

from memory 47ohm 10watts is what's required 😱

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3 hours ago, Loddon said:

from memory 47ohm 10watts is what's required 😱

Just measured the bulb resistance cold and it is 33 ohms. Should be OK to flow enough current to the alternator. All new wires and connectors between. The engine doesn't turn very fast, but there is quite a high ratio between the crank and alternator pulleys.

Jen

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41 minutes ago, Jen-in-Wellies said:

Just measured the bulb resistance cold and it is 33 ohms. Should be OK to flow enough current to the alternator. All new wires and connectors between. The engine doesn't turn very fast, but there is quite a high ratio between the crank and alternator pulleys.

Jen

 

But the resistance will be far more when it's hot because incandescent bulbs have a positive temperature coefficient, plus about 3 to 4 ohms of rotor resistance in series with it.  I suspect that may be a 2.2 watt MES bulb and they are normally fine to energise alternators, I suspect it's just a low idle speed so easy to solve with a little rev as it starts. I am not sure that you can easily get a higher wattage MES bulb with a typical small glass, the more powerful ones, when you can find them, have a bigger globe so may not fit the warning lamp.

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21 minutes ago, Tony Brooks said:

Let's have a photo of the bulb, it might be a 1.5 watt and that will need a resistor.

No can do I'm afraid. It is a sealed unit. See https://www.ebay.co.uk/itm/271254193428

It looks identical to the ones in my Beta panel that are used for alternator warning.

Except it is blue, rather than red. Perhaps that is it! 😀

 

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Thank Jen, it is almost certainly and LED or grain of wheat (dolls house) bulb and in most cases they will not energise a typical alternator. These stand a better chance of energising it https://www.vehiclewiringproducts.co.uk/c-63-warning-lights/p-760-warning-light-with-replaceable-bulb but at 1.5W it can be marginal. It should be a push in replacement. Otherwise, it's fit a resistor. A fitting for a 2.2W or 6W bulb will probably need the hole enlarging.

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Posted (edited)
48 minutes ago, Tony Brooks said:

Thank Jen, it is almost certainly and LED or grain of wheat (dolls house) bulb and in most cases they will not energise a typical alternator. These stand a better chance of energising it https://www.vehiclewiringproducts.co.uk/c-63-warning-lights/p-760-warning-light-with-replaceable-bulb but at 1.5W it can be marginal. It should be a push in replacement. Otherwise, it's fit a resistor. A fitting for a 2.2W or 6W bulb will probably need the hole enlarging.

Cheers Tony,

Definitely not an LED, so teeny incandescent bulb is most likely. I'll dig up a suitable power resistor to parallel with it.

 

Edited to add: The bits box has offered up a 15 ohm 10W resistor. Will this do? IsquaredR says power is on the limit.

Edited by Jen-in-Wellies
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18 minutes ago, Jen-in-Wellies said:

Cheers Tony,

Definitely not an LED, so teeny incandescent bulb is most likely. I'll dig up a suitable power resistor to parallel with it.

 

Edited to add: The bits box has offered up a 15 ohm 10W resistor. Will this do? IsquaredR says power is on the limit.

I would suggest suck it and see, but make sure it's not touching anything that would be damaged if it burned/got red-hot. I think it will be OK because you have that rotor resistance in series, so it's at least 18 or 19 ohms.

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5 minutes ago, Tony Brooks said:

I would suggest suck it and see, but make sure it's not touching anything that would be damaged if it burned/got red-hot. I think it will be OK because you have that rotor resistance in series, so it's at least 18 or 19 ohms.

 

Turn it on. See if it blows up. Proper science!

Frankenstein-James-Whale-1931.png.eb0721391e19d7d5723495915f883a7a.png

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42 minutes ago, Jen-in-Wellies said:

 

Turn it on. See if it blows up. Proper science!

 

Get someone else to turn it on.  See if it blows up.  Take notes.

 

Reproducible experiments are the best sort of science ...

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Posted (edited)
8 hours ago, TheBiscuits said:

 

Get someone else to turn it on.  See if it blows up.  Take notes.

 

Reproducible experiments are the best sort of science ...

You need the right sort of person to do the turning on. Seventy plus years of the NHS means that severely hunch backed lab assistants are hard to find. Fortunately, its stealth privatisation will ensure that future generations of mad scientists have the proper assistance their profession demands.

Edited by Jen-in-Wellies
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11 hours ago, Tony Brooks said:

I would suggest suck it and see, but make sure it's not touching anything that would be damaged if it burned/got red-hot. I think it will be OK because you have that rotor resistance in series, so it's at least 18 or 19 ohms.

It should be (just about) OK - but in normal use it shouldn't be dissipating very long, unless you are in the practice of leaving the ignition on and the engine not running for long periods...

 

(if it's getting hot there is current flowing - if current is flowing and the engine is spinning the alternator will excite, if the alternator excites it will provide its own current and resister will no longer get hot...)

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Seems to have worked. The resistor gets hot, but still touchable with the switch on and engine stopped. There is 8 to 10W being consumed inside, so to be expected. It is well clear of anything else behind the panel. Alternator excites straight away now.

Jen

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12 hours ago, Jen-in-Wellies said:

 

Turn it on. See if it blows up. Proper science!

Frankenstein-James-Whale-1931.png.eb0721391e19d7d5723495915f883a7a.png

 

When I first started work, one building had a switchboard like that.

 

Didn't have the patient though! I always regretted not improvising, using my then boss. 🤣

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57 minutes ago, Jen-in-Wellies said:

Seems to have worked. The resistor gets hot, but still touchable with the switch on and engine stopped. There is 8 to 10W being consumed inside, so to be expected. It is well clear of anything else behind the panel. Alternator excites straight away now.

Jen

 

Good, but it seems a lot of trouble for the sake of a £3 lamp that will be very likely to work.

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35 minutes ago, Tony Brooks said:

 

Good, but it seems a lot of trouble for the sake of a £3 lamp that will be very likely to work.

Back when I had this problem I tried several lamps some of which worked better than others, none worked properly. Fitted the resistor and it all worked as it should with charging starting  on tickover. 😎

Edited by Loddon
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As long as it energises with  a few revs I don't see it as a problem, more a feature to be expected. Yes, you can force it energise the at tickover, but it seems a bit pointless to add complications. I know that nowadays some marinisers fit a resistor as standard, but that is often because for cost, aesthetic, or reliability issues they fit a lamp with a grain of wheat bulb or an LED.

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40 minutes ago, Tony Brooks said:

As long as it energises with  a few revs I don't see it as a problem, more a feature to be expected. Yes, you can force it energise the at tickover, but it seems a bit pointless to add complications. I know that nowadays some marinisers fit a resistor as standard, but that is often because for cost, aesthetic, or reliability issues they fit a lamp with a grain of wheat bulb or an LED.

When all filament bulb are finally banned, they will all be LED with a resistor.  Beta have done that for many a year.  The resistors in their panels do burn out.

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