How to shutdown the alternator ?

[rom]

Hi everyone,

I am looking for a simple way to disconnect/reconnect the alternator. The reason is I have lots of solar and I only need the alt very few days a year.

Is it something an external regulator can do ? I do not need 3 stage or anything "smart" though.

cheers

[smac999]

why? if the batteries are full, nothing much will come out of it anyways. so it won't make any difference if it's on or not.

otherwise most likely you'd want an external reg so you can shut that off.

if you have a non self exciting alt. you can probably cut the ignition input. but would have to do that before engine started. I think if it did it during it wouldn't shut off.

if you disconnected the pos alt cable before starting the engine. it would also work. but if you disconnected durring running, you'll blow it up.


do your solar charge your engine battery? if you running the engine with no alt, and only charging the house will solar. that's not going to work anyways.

[sailormed]

KISS solution: remove belt

[double u]

whoa! cooling water pump!!!

[rom]

Originally Posted by smac999

why? if the batteries are full, nothing much will come out of it anyways. so it won't make any difference if it's on or not.

otherwise most likely you'd want an external reg so you can shut that off.

if you have a non self exciting alt. you can probably cut the ignition input. but would have to do that before engine started. I think if it did it during it wouldn't shut off.

if you disconnected the pos alt cable before starting the engine. it would also work. but if you disconnected durring running, you'll blow it up.


do your solar charge your engine battery? if you running the engine with no alt, and only charging the house will solar. that's not going to work anyways.

It would be a waste of energy to have the alternators feeding the batteries while motoring in the morning when I know for sure that the solar panels alone would charge them 100% by midday.

FYI, I am removing the starter batteries so that everything runs on the house batts. I will have a safety batt connected to the system with a 1/2/both/off switch. Also there is only one cable (well 2, pos & neg) going to the alt/starter so I can not switch it off before or after starting the engines.

[Pete7]

Originally Posted by smac999

why? if the batteries are full, nothing much will come out of it anyways. so it won't make any difference if it's on or not.

Hmm, my thoughts too, why complicate something when you know it will fail at sea just at the worst possible moment.

Pete

[Maine Sail]

Originally Posted by rom

It would be a waste of energy to have the alternators feeding the batteries while motoring in the morning when I know for sure that the solar panels alone would charge them 100% by midday.

Considering the physical time it takes to get a lead acid battery to 100% SOC, due to slow acceptance rates at high SOC's, there are very few scenarios where solar could get a deep cycled house bank back to 100% SOC by mid day.

If you believe your solar is capable of this, though it would be extremely rare, then the alt does not need to be turned off anyway because it won't be doing much of anything and solar can easily turn it off, if the set point is set properly for what you desire... If the solar can't get voltage above the alts voltage limit, and shut it down, then you essentially needed the alt anyway and the PV was inadequate to do the job..

Even high acceptance rate AGM batteries charged at .4C, or 40% of Ah capacity (40A for a 100Ah battery or 180A for a 450Ah bank), still take about 5.5 hours to attain 100% SOC from a 50% DOD starting point. Other types of lead acid batteries take considerably longer, especially when the controller drops to float prematurely, as many solar controllers do.

Some high current bulk charging in the morning is the optimal way to blend solar and dino juice. Bulk charging in the AM then allows solar to slowly feed the rest of the energy into the bank throughout the day. In many cases there are not enough solar hours in a day to get lead acid batteries back to 100% SOC.

In order to safely turn off an alternator the field needs to be interrupted (open circuit the brush). If you already have an external regulator simply put a switch in the ignition feed to the regulator and this will shut down the alt....

[CatNewBee]

Well electricity basics:

- a current only flows if there is a voltage difference between source and destination.

The alternator produces 14.2...14.4V (regulator output)
The solar controller probably delivers 14.7..14.8V with AGM battery settings - otherwise 14.3..14.4V

so no current is expected from alternator to battery.

If there is no sun (motoring during the night) the batteries will be charged by the alternator - and that is OK anyway.

Why solve a problem, that does not exists in the real world?

[fallingeggs]

Originally Posted by Pete7

Hmm, my thoughts too, why complicate something when you know it will fail at sea just at the worst possible moment.

Pete

Same. Why complicate when there is zero benefit (and possibly a negative effect if a solar controller fails) to doing so?

[Dockhead]

Yes, much truth to all of this, but no one has answered the OP's actual question.

The answer is most alternators can indeed be "turned off" electrically. My school bus alternator will not produce power without 24 volts on the exciter terminal. Switch off the power, and it stops charging. Some alternators are "self exciting" -- I can't say what to do with them, but an alternator like mine can most definitely be just switched off.

The Balmar external regulator I believe will also do this -- there is a switch you can use when you need maximum power from the main engine for propulsion, if I am correctly informed.


I do agree though that there is little point in doing this. It's almost free power unless you have a very small main. But the OP was not asking for advice about WHETHER to do it; he wanted to know HOW.

[rom]

Originally Posted by Maine Sail

Considering the physical time it takes to get a lead acid battery to 100% SOC, due to slow acceptance rates at high SOC's, there are very few scenarios where solar could get a deep cycled house bank back to 100% SOC by mid day.

If you believe your solar is capable of this, though it would be extremely rare, then the alt does not need to be turned off anyway because it won't be doing much of anything and solar can easily turn it off, if the set point is set properly for what you desire... If the solar can't get voltage above the alts voltage limit, and shut it down, then you essentially needed the alt anyway and the PV was inadequate to do the job..

Even high acceptance rate AGM batteries charged at .4C, or 40% of Ah capacity (40A for a 100Ah battery or 180A for a 450Ah bank), still take about 5.5 hours to attain 100% SOC from a 50% DOD starting point. Other types of lead acid batteries take considerably longer, especially when the controller drops to float prematurely, as many solar controllers do.

Some high current bulk charging in the morning is the optimal way to blend solar and dino juice. Bulk charging in the AM then allows solar to slowly feed the rest of the energy into the bank throughout the day. In many cases there are not enough solar hours in a day to get lead acid batteries back to 100% SOC.

Thank you for the taking the time to answer. I do not think my solar will get me to 100%, I know.

Why ? Because I have spent the last 400 days disconnecting my alternors from my house batterie and I have reached 100% SOC almost every day, except those rare occasions where solar was not enough, really not. Yes I know how to know when 100% is reached.

How did I do that ? I have still not finished my electical system modification and thanks to the old system I can simply disconnect the alts from the house while they are still connected to the starter batteries.

Why am I asking this now ? Because I will soon finish the system and get rid of the starter batteries in favor of a safety batterie. Everything will be directly connected to the house bank. (partly based on your excellent suggestion of 1/2/both/Off system BTW).

Side note: I have 1000Ah@12V gel, 1320W solar.

Originally Posted by Maine Sail

In order to safely turn off an alternator the field needs to be interrupted (open circuit the brush). If you already have an external regulator simply put a switch in the ignition feed to the regulator and this will shut down the alt....

Good ! as I said I don't need anything smart, what would be cheapest reg that does the job ?

[rom]

Originally Posted by Dockhead

Yes, much truth to all of this, but no one has answered the OP's actual question.

The answer is most alternators can indeed be "turned off" electrically. My school bus alternator will not produce power without 24 volts on the exciter terminal. Switch off the power, and it stops charging. Some alternators are "self exciting" -- I can't say what to do with them, but an alternator like mine can most definitely be just switched off.

The Balmar external regulator I believe will also do this -- there is a switch you can use when you need maximum power from the main engine for propulsion, if I am correctly informed.


I do agree though that there is little point in doing this. It's almost free power unless you have a very small main. But the OP was not asking for advice about WHETHER to do it; he wanted to know HOW.

Thank you Dockhead for taking the time to answer. I will probably need to do some modifications to my original hitachi alts as they are indeed "self exciting". Engines are yanmar 4JH4.

Let me however respectfully disagree with you about "almost free power" from the alt. Increased full consumption, wear on the belt, dust, wear on the alt, increased heat in engine room. Plus incorrect (too high) floating voltage when batts are already at 100% SOC. I may be wrong on that last one though.

[CatNewBee]

Just put a relais / solenoid / switch in the + wire of the alternator - if this is your concern.

When there is no current, the alternator runs in "no-load" mode - there will be almost no resistance on the belt if no power is drawn.

Otherwise you can mis-use an electro-mechanic coupling instead of the original V-belt disk (e.g. from a car air-conditioner compressor) to de-coupe the alternator shaft from the v-belt, so the alternator will not turn any more while the alternator disk / V-belt / water pump keeps turning.

[Dockhead]

Originally Posted by CatNewBee

Just put a relais / solenoid / switch in the + wire of the alternator - if this is your concern.

When there is no current, the alternator runs in "no-load" mode - there will be almost no resistance on the belt if no power is drawn.

Otherwise you can mis-use an electro-mechanic coupling instead of the original V-belt disk (e.g. from a car air-conditioner compressor) to de-coupe the alternator shaft from the v-belt, so the alternator will not turn any more while the alternator disk / V-belt / water pump keeps turning.

What do you mean by "+ wire of the alternator"? If you're talking about the main connection to the batteries, then do NOT please do this -- you will blow the diodes.

[Dockhead]

Originally Posted by rom

Thank you Dockhead for taking the time to answer. I will probably need to do some modifications to my original hitachi alts as they are indeed "self exciting". Engines are yanmar 4JH4.

Let me however respectfully disagree with you about "almost free power" from the alt. Increased full consumption, wear on the belt, dust, wear on the alt, increased heat in engine room. Plus incorrect (too high) floating voltage when batts are already at 100% SOC. I may be wrong on that last one though.

OK, it's your boat. You don't need to justify your plans.

I hope we answered your question. Please let us know how it turns out.