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Old 17-07-2020, 12:34   #1
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How to take the alternator out of charging if all power is needed to run engine???

In another thread I had it came up that a switch can be used to remove the alternator from charging up if for some reason all engine power outputs were needed to get boat away from some hazardous situation

How can I devise this solution for my boat engine is Yanmar 2ym15 with a 80 amp ReMar 80 Amp alternator

Not sure if this question is electronic or engine issue solution ??

Thanks
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Old 17-07-2020, 13:55   #2
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How to take the alternator out of charging if all power is needed to run engine???

Put a simple on off switch in the field wire
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Old 17-07-2020, 17:02   #3
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How to take the alternator out of charging if all power is needed to run engine???

As Ecos posts, you need a switch to interrupt the field circuit however be aware that on some (many?) stock alternators, once the the alternator is up to speed, the field circuit is controlled internally. In these alternators, you need to modify them to access the field circuit.
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Old 17-07-2020, 17:16   #4
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Re: How to take the alternator out of charging if all poet is needed to run engine???

Turn off the key field power is supplied by the key switch. If a regular thing, put a swirch in the circuit.

Matt
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Old 17-07-2020, 18:10   #5
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How to take the alternator out of charging if all power is needed to run engine???

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Originally Posted by mlydon View Post
Turn off the key field power is supplied by the key switch. If a regular thing, put a swirch in the circuit.

Matt
The key switch only provides the initial field excitation on some (many?) stock alternators. Once the alternator reaches it's "rise speed", it becomes self exciting and the key switch has no effect on the output of the alternator.

Turning the key switch OFF before starting will ensure these alternators will remain OFF but of course, this requires a start switch that is independent of the key switch.
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Old 17-07-2020, 19:53   #6
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How to take the alternator out of charging if all power is needed to run engine???

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Turning the key switch OFF before starting will ensure these alternators will remain OFF but of course, this requires a start switch that is independent of the key switch.
And, at least for us, it is convenient to have.
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Old 18-07-2020, 00:55   #7
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Re: How to take the alternator out of charging if all power is needed to run engine??

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Originally Posted by JPA Cate View Post
And, at least for us, it is convenient to have.


Yep, I have a start button down in the engine box, handy if you need to crank the engine to bleed an injector or electrical problems with the key switch.
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Old 18-07-2020, 02:50   #8
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Re: How to take the alternator out of charging if all power is needed to run engine??

@ eco
How do I find the feild wire on alternaor as there is positive negative and then box inputs in block and no earth .



I was of the opinion from other sources if I turn off the key after engine starts that this will burn out the diodes in the alternator.

My alternator is ReMar 80 amp basically a more powerful Yanmar clone type to replace the OEM Yanmar 35 and 55 amp alternator

The engine is a Yanmar 2YM15 and the dash board is pre 1990 older type simplex with RPM and key turn kill engine button and four idiot light s one for oil pressure alarm one for engine temp alarm and other two idiot lights unknown.

I suspect I will change to low power ~ 9 HP type Yanmar engine where alternator power demands might be too much

There exist the risk a depleted battery such as start battery 80 amp might demand too many amps and drag too much power from the engine so to remove alternator from drive train will allow engine to give maximum power to the propeller

@ wotname

I must look that idea of start button in engine region that by passes the key start any online diagrams I can follow

Then engine can be started by the engine start button or hand crank ( not available on my engine ) means alternator doesnt switch on is what I think you and others are saying

Thanks for info so far
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Old 18-07-2020, 04:22   #9
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Re: How to take the alternator out of charging if all power is needed to run engine??

If you really wish to remove the mechanical load of the alternator, (which is approx 1 HP) from the engine output, the only practical way is to take off the drive belt. But, what sort of emergency does the OP envisage that requires every single microwatt of power delivered to the prop? And, by the solution he's proposing, it will compromise his electrics, because, by definition, he's not charging his batteries.
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Old 18-07-2020, 04:40   #10
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Re: How to take the alternator out of charging if all power is needed to run engine??

Without the initial excitation provided by the current through the warning lamp the alternator will not start charging at all and consequently there will be no internal power provided to the regulator.

You could install a switch in the circuit for the warning light to stop the alternator from starting to charge and it would still allow you to use the key to start the engine. However you would have to ensure the switch was used to break the circuit before you started the engine.
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Old 18-07-2020, 09:25   #11
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Re: How to take the alternator out of charging if all power is needed to run engine??

I'm with Parkstone Bay. Why would you ever need to do this?
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Old 18-07-2020, 09:40   #12
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Re: How to take the alternator out of charging if all power is needed to run engine??

It is a common misconception that turning off the alternator field will damage it. The damage only occurs if you disconnect the alternator output.

Not familiar with Yanmar but on most engines the alternator belt also turns the fresh water circulating pump. Very bad idea to remove the belt. You would cook the engine.

Since most internally regulated alternators only produce full output for a very short time just don't worry about the power loss. Keep in mind that mechanical load on an alternator is directly related to alternator output current. If you have an external regulator just switch off the input power to it. Don't mess with the field wire. Switching off the field wire of an external regulator means that it will still be trying to control the alternator. Most will have protections for an open field, some may not.
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Old 18-07-2020, 10:57   #13
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Re: How to take the alternator out of charging if all power is needed to run engine??

The real question is why an 80 amp alternator on a 16hp motor. You'd need huge battery amperage, 400 amp plus or exotic batteries to be able to use 80 amp output and then only for a short period before the regulator cuts back alternator output. Think you'd be better off with smaller alternator with an external multi-stage regulator. The external regulator would give you the ability to cut the field current. Assume you have a Hitachi internal regulator alternator which makes cutting the field impossible once it takes over.
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Old 18-07-2020, 11:57   #14
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Re: How to take the alternator out of charging if all power is needed to run engine??

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Think you'd be better off with smaller alternator with an external multi-stage regulator. The external regulator would give you the ability to cut the field current.
I'm with roverhi on this one. If you think you need more control of your system, this is a better way to do it.
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Old 18-07-2020, 13:11   #15
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Re: How to take the alternator out of charging if all power is needed to run engine??

Two 9 hp yanmars in my cat. The sb engine could not cope with the charging right from starting, so I switched off the contact for a minute.
Being warmed up a bit I turned the key again and there was no problem anymore. With higher revs, far more power than the alternator required, so that 1hp did not make much difference. It easily reached max revs.
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