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Old 19-11-2018, 17:50   #1
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Yanmar SB12 Alternator Upgrade?

Any fellow SB12 owners who have upgraded their alternator care to share your thoughts? Pros/cons, which you chose, how it's worked out, etc. Thanks!
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Old 20-11-2018, 21:30   #2
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Re: Yanmar SB12 Alternator Upgrade?

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Any fellow SB12 owners who have upgraded their alternator care to share your thoughts? Pros/cons, which you chose, how it's worked out, etc. Thanks!
*crickets*
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Old 21-11-2018, 02:53   #3
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Re: Yanmar SB12 Alternator Upgrade?

"upgraded their alternator"


Can you elaborate as to what you mean? Do you mean a later model, increased amps? (maybe more efficient?)



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Old 21-11-2018, 04:47   #4
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Re: Yanmar SB12 Alternator Upgrade?

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"upgraded their alternator"


Can you elaborate as to what you mean? Do you mean a later model, increased amps? (maybe more efficient?)



Clive
Clive, that's exactly what I mean. The stock alternator is 35 amp. Wondering if anyone has installed a later model alternator with higher amperage output on their SB12, which model, and how it has worked out (fuel use, power, temperature, etc). Thanks!
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Old 21-11-2018, 15:57   #5
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Re: Yanmar SB12 Alternator Upgrade?

Depending how far you go but you might have to go from a single groove pulley to two groove which can complicate matters. (Anything over 70A and you will have to think about going to two groove pulleys) This article will help explain the problems.

https://www.westmarine.com/WestAdvis...-an-Alternator

I'm currently replacing my Perkins 4-108 12V 35A(?) alternator with a 24V 60A alternator which is not easy. Many people have upgraded using an after market alternator and serpentine belt pulleys but the cost is well over $US1000.


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Old 21-11-2018, 16:55   #6
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Re: Yanmar SB12 Alternator Upgrade?

Just remember you don't have a lot horsepower available with the SB12.
A very rough rule of thumb is you will use 1 hp to get 50 amps out of a 12V alternator.
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Old 21-11-2018, 18:02   #7
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Re: Yanmar SB12 Alternator Upgrade?

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Just remember you don't have a lot horsepower available with the SB12.
A very rough rule of thumb is you will use 1 hp to get 50 amps out of a 12V alternator.
Good to know. I installed a switch so I can d/c the alternator lead if I don't want it to draw....but on the flip side I would like to be able to charge slightly more rapidly if necessary. I can't see a situation where I would need both rapid charging and max HP concurrently.
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Old 21-11-2018, 18:12   #8
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Re: Yanmar SB12 Alternator Upgrade?

The rule of thump is 24 amps at 12V will take 1 HP.
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Old 21-11-2018, 18:47   #9
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Re: Yanmar SB12 Alternator Upgrade?

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The rule of thump is 24 amps at 12V will take 1 HP.
Thanks for that. That is something I'll commit to memory.
Apparently the reasoning goes something like.

QUORA
Tony Christian Ratcliffe, studied Electronics at St Albans, Hertfordshire (1986)
Answered Jun 6
I am assuming that you are talking about a car alternator so here goes.
80 x 14.5 = 1160 watts ( despite the 12V battery the alternator output is nearer 14.5v)
1160 watts = 1.55 Hp if 100% efficient. An alternator is nearer 55%.
You therefore lose approximately 2.75 Hp driving the alternator if it is under load.


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Old 21-11-2018, 19:39   #10
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Re: Yanmar SB12 Alternator Upgrade?

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Originally Posted by coopec43 View Post
Thanks for that. That is something I'll commit to memory.
Apparently the reasoning goes something like.

QUORA
Tony Christian Ratcliffe, studied Electronics at St Albans, Hertfordshire (1986)
Answered Jun 6
I am assuming that you are talking about a car alternator so here goes.
80 x 14.5 = 1160 watts ( despite the 12V battery the alternator output is nearer 14.5v)
1160 watts = 1.55 Hp if 100% efficient. An alternator is nearer 55%.
You therefore lose approximately 2.75 Hp driving the alternator if it is under load.


Clive
That comes out to 29 amps per HP. He didn't take into account the belt loses and only considered the alternator efficiency. Either way it gives you a ballpark figure to look at.
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Old 21-11-2018, 20:50   #11
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Re: Yanmar SB12 Alternator Upgrade?

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Any fellow SB12 owners who have upgraded their alternator care to share your thoughts? Pros/cons, which you chose, how it's worked out, etc. Thanks!
We have a 55amp Bosch alternator on our Ysm8 .Didnt get enuff out of the 35amp Hitachi, it had a thermal cutout that kept cutting it out when we tried to charge our battery bank. The 55 amp is driven by a single belt & we have a switch in the field wire in the instrument panel so we can cut it out as it draws a noticeable amount of power out of our 7hp continuous rated engine.
Used it a lot until we had a solar upgrade with no trouble. Will be even better for you with your more powerful engine as we are a little under-powered for powering the boat along. I removed the Hitachi but I'm considering re-installing so I can run both if using the engine solely for charging at anchor if we get a few low solar days in a row. I think it will mean we can run at lower revs using 2 at once which will be nice for the noise factor alone.
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Old 02-12-2018, 16:44   #12
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Re: Yanmar SB12 Alternator Upgrade?

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We have a 55amp Bosch alternator on our Ysm8 .Didnt get enuff out of the 35amp Hitachi, it had a thermal cutout that kept cutting it out when we tried to charge our battery bank. The 55 amp is driven by a single belt & we have a switch in the field wire in the instrument panel so we can cut it out as it draws a noticeable amount of power out of our 7hp continuous rated engine.
Used it a lot until we had a solar upgrade with no trouble. Will be even better for you with your more powerful engine as we are a little under-powered for powering the boat along. I removed the Hitachi but I'm considering re-installing so I can run both if using the engine solely for charging at anchor if we get a few low solar days in a row. I think it will mean we can run at lower revs using 2 at once which will be nice for the noise factor alone.
Well, sure enough, I went ahead and started thinking about the alternator.....a week later and it seems that my 40 y/o unit has died. I'll take it apart and do what I can to revive it. But...

Mind sharing the model number on that Bosch? Seems like it might be an appropriate upgrade.

Thanks!
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Old 02-12-2018, 17:11   #13
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Re: Yanmar SB12 Alternator Upgrade?

Sure I'll give it to you but it wont be for a couple of weeks as going to sea & wont be able to get online till I get back. It's an oldie tho so don't know if they still made. Any 50 amp older style alternator will do as long as you know how to wire it up. I'm no electrical expert but followed advice on the alternator bible ( available for free online )
It looks like this roughly :020403625 - BOSCH ALTERNATOR 12V DEUTZ 55 AMP [020403625] - R0.00 : FAE Online parts catalogue
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Old 03-12-2018, 05:21   #14
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Re: Yanmar SB12 Alternator Upgrade?

Well in researching further I'm beginning to think that with my new battery bank an old style alternator might just not be up to the task. I'm thinking the CMI-80-ER - 80A from Marine How To is probably the best option for my setup. Thoughts?

Edit: I have a Yanmar SB12 engine with stock 35a alternator leading to Blue Sea Systems off/on/combine switch. Starting battery is 65ah FLA, through Blue Sea Systems ACR to the house bank which is 3 group 27 AGMs (90ah/ea) for 270 ah house bank total.

Additionally I have 260 watts of solar feeding the batteries through a dual battery PWM charge controller.

My major power draw is the new fridge, but also have cell phone charger, all the regular boat stuff (lights, vhf, chartplotter, etc) and a 1000w inverter that I use rarely to charge the laptop or run a dremel.
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Old 03-12-2018, 06:18   #15
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Re: Yanmar SB12 Alternator Upgrade?

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Originally Posted by pmagistro View Post
Edit: I have a Yanmar SB12 engine with stock 35a alternator leading to Blue Sea Systems off/on/combine switch. Starting battery is 65ah FLA, through Blue Sea Systems ACR to the house bank which is 3 group 27 AGMs (90ah/ea) for 270 ah house bank total.
So the question you need answering is what is the maximum current those AGMs will accept when heavily discharged? For us with a FLA house bank its C.2 or 20% of the battery bank AH. So 2 x 110AH batteries will take a maximum charge of 44A. In practice I haven't seen above 42A from the alternator and that drops quickly as the batteries charge. Therefore decided to keep things simple and stick with our standard 60A alternator. Couldn't see the point of going for anything bigger. Mainsail does explain this in one of his articles, but might be on his old website. You may find a smaller standard car alternator a cheaper option.

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Additionally I have 260 watts of solar feeding the batteries through a dual battery PWM charge controller.
That's nice but how about changing the PWM for one of the small Victron MPPTs to maximise the solar panels output? The small ones are cheap enough and have a good reputation on here. I had no problem selling both of my PWMs to help offset the cost.

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