Alternators and horsepower

bearsails · Mar 31, 2015

Hey Richard

Those numbers are pretty close, but, it isn't likely you will charging that heavy for that long, that is assuming full load charging - i.e, - batteries are way down and you are hitting them with all you have, once the charge rate drops the HP loss drops as well so you would likely be OK going to a bigger alternator.
I have an 84 H31 and we have gone to great lengths to reduce power consumption - all LED lighting, no refrigeration, no water pump, etc., my boat has a Universal M25 3 cylinder diesel as auxiliary power (long story) and a 50 amp alternator which never really has to work too hard.
The Yanmar 2GM is a great power plant but a little on low HP side for a 10,000 pound boat against a headwind or tide, but it was considered more than adequate when the boat was designed and it is a sailboat!

Have fun

Mike

mz4wheeler · Mar 31, 2015

It isn't a constant load of 2HP. You usually only get a load when you first start the engine and the alternator is heavily charging. Assuming your batteries are good, they will charge quickly and the load on the engine will be reduced. Just start it up and let it warm up [grin].

kloudie1 · Mar 31, 2015

Richard, here is the math of it.. 1 Kilowatt is 1.341 horsepower.. The alternators are somewhere around 50% efficient at turning horsepower to kilowatts
1 Kilowatt at 14 volts is 71.4 amperes the efficiency thing makes a rough guess at 35.7 amperes will suck 1 horsepower from the engine.. again, the belt drive will take another 2% or so .. then you are talking a number like 35 amperes = 1 alternator horsepower.. 70=2 HP, 105 a=3 HP.. 140 A = 4 HP.. These are thumbnail numbers and aren't exact.. the thing that gets ya is the power curve of the engine.. For instance, a 1GM is rated at 6.5 HP .. At a nominal 2400 rpm, it can only make a smidge over 4 hp. at that RPM, a typical propeller will suck a smidge over 2 HP leaving you with an overload at 70 amperes. if the alternator does not have a field limiter, the engine would probably not be able to start, since a 70 ampere alternator would be trying to make almost full power at start; and the engine could not sustain that much load.. A 2 GM or 3GM would probably be OK with that much start load, but any larger alternator would require a field limiter on startup..

woodster · Mar 31, 2015

so based on the numbers Kloudie1 has given....then one could put in an 80 amp balmar and limit it to 60 amp max output and only be using approx.... 1 3/4 hp ...on a 2gm20f... that would be a good setup ...they are rated at 14 hp to 18 hp depending on who is telling that lie.... lol so on the low end you would still have 12.5 hp to push the 10,000 lb barge opps i mean boat lol that should be ok i would think and if you need more power then just pull the jib out some because if you are in rough water there must be wind unless its in a shipping lane with a gazillion ships on the move..... and this is assuming your batts need a good charge

Ralph Johnstone · Mar 31, 2015

wufibugs said:
it is clear that my 35 amp is inadequate for refrigeration, gps, stereo, lighting, computers, phone chargers, autopilot, and heaven knows what else folks are plugging in.

It may be that it just isn't doing its job.

The alternator on my Yanmar 2GM20F (HITACHI ALTERNATOR, LR155-20B, 129772-7720, 12VOLT - 55AMP) hadn't done much more than the absolute minimum since I bought the boat new. 14.2V output and that's all you get. Not enough to fry the batteries, not enough to fully charge them either. Installed a Balmar ARS-5 external alternator regulator and put the alternator to work at 14.7V on bulk. Battery monitor shows that several hours of motoring and I'm back to 100% SOC.

woodster · Mar 31, 2015

Ralph Johnstone said:
It may be that it just isn't doing its job.

The alternator on my Yanmar 2GM20F (HITACHI ALTERNATOR, LR155-20B, 129772-7720, 12VOLT - 55AMP) hadn't done much more than the absolute minimum since I bought the boat new. 14.2V output and that's all you get. Not enough to fry the batteries, not enough to fully charge them either. Installed a Balmar ARS-5 external alternator regulator and put the alternator to work at 14.7V on bulk. Battery monitor shows that several hours of motoring and I'm back to 100% SOC.

did you convert the alt to external regulator Ralph ?

woodster · Mar 31, 2015

wufibugs said:
Is the stock Hitachi 35 alternator loafing because of the thermal limiter?

it could be...... from what i have read on here they slow down when they get to a certain temp...... a built in safety valve if you will ...according to what i have read the stock alts never really put out there full rating

Stu Jackson · Mar 31, 2015

Here it is again:

Hitachi/Yanmar Alternators: (by Maine Sail)

Some alternators though, such as those made by Hitachi and found on Yanmar diesels, are dumber than a pound of beetle poop. Actually, to the alternator, they are pretty smart but to your batteries and the speed of charging they are flat out stupid. Why?

Hitachi alts with dumb regulators, and some others, limit voltage but also reduce voltage based on alternator temperature. This is a self protective feature installed in the internal dumb regulator to prevent the alternator from cooking itself. Remember voltage is the pressure that allows more current to flow. So, if we reduce the absorption voltage, then we also reduce the current the alternator is supplying.. The battery simply will not accept the same current at 13.4V that it did at 14.4V and as a result the alternator will run cooler. What do you suppose this does to your batteries over time.......?

The problem is that when cold you will get 14.3V to 14.4V out of the Hitachi but as the alternator heats up the dumb regulator begins to reduce the CV/voltage limit based on the alternators internal temperature. It is not uncommon to find a Hitachi alternator at 13.4V when hot. This is REALLY, REALLY DUMB....

If you have a dumb regulator, and notice the voltage dropping, it is likely a temp compensated dumb regulator. Get rid of it or plan to buy new batteries more often.

If you have a temp compensated alternator or a Hitachi alternator on a Yanmar you really are in dire need of external regulation if deep cycling a larger battery bank.

This is from:

http://forums.sbo.sailboatowners.com/showthread.php?t=125392

and this, too:

http://www.cruisersforum.com/forums...d-smart-regulator-instal-question-125843.html

okawbow · Mar 31, 2015

I did a lot of cruising on a Cheoy Lee 31, with an 18 hp diesel. Before I started, I installed a 105 amp alternator and 2 gel cell batteries. I never noticed any problems with engine power, and I did a lot of motoring against current. I could always get hull speed easily if there wasn't too much current. I replaced a 35 amp alternator and couldn't really see a difference in boat performance.

Stu Jackson · Mar 31, 2015

wufibugs said:
The issue is how much horsepower loss will my little 18 hp Yanmar suffer were I to go up to 65, 80 or even 105 amp alternator?

As mentioned earlier, battery acceptance will determine the "required" output based on what the regulator is telling the alternator to do.

If BA is 30 A then all three of these alternators will produce 30A.

The SOC and size of the bank will determine that.

I have a100A alternator on our M25. With a 50% SOC at 100% (Small Engine Mode - SEM - OFF, with NO belt (amp) manager) I see 60A on a 390 ah house bank.

I use SEM (50% on our MC-612) when I startup if I'm going to hit cruising rpms soon after pulling the hook. When the amperage drops to 30 after maybe half an hour or so, I kick the SEM off, and get back to 60A charging for a short time as the battery acceptance decreases.

If I'm at anchor, I'll run the engine to 1500 rpm, with SEM OFF - 100%, but the lower rpms decrease the output.

It's a management issue.

Maine Sail recommends the use of Belt Manager, in lieu of SEM, connecting those contacts to an alternator temp sensor.

Your boat, your choice.

Alternator heat, Regulator Controls, Small Engine Mode

http://c34.org/bbs/index.php/topic,4454.0.html

Small Engine Mode - discussion with link to the picture of the toggle switch: http://c34.org/bbs/index.php/topic,4454.msg27149.html#msg27149

woodster · Mar 31, 2015

Ralph Johnstone said:
It may be that it just isn't doing its job.

The alternator on my Yanmar 2GM20F (HITACHI ALTERNATOR, LR155-20B, 129772-7720, 12VOLT - 55AMP) hadn't done much more than the absolute minimum since I bought the boat new. 14.2V output and that's all you get. Not enough to fry the batteries, not enough to fully charge them either. Installed a Balmar ARS-5 external alternator regulator and put the alternator to work at 14.7V on bulk. Battery monitor shows that several hours of motoring and I'm back to 100% SOC.

so let me try this again ....

Ralph...when you put the balmar ARS-5 external alternator regulator.....

did you keep the yanmar 55 amp alt and if so did you convert it to external regulated ...

or am i to assume that all you did was put on a balmar ARS-5 and hook it up to the yanmar regulator as it came from the factory

Hello Below · Mar 31, 2015

woodster said:
so let me try this again .... Ralph...when you put the balmar ARS-5 external alternator regulator..... did you keep the yanmar 55 amp alt and if so did you convert it to external regulated ... or am i to assume that all you did was put on a balmar ARS-5 and hook it up to the yanmar regulator as it came from the factory

Found an old post from Ralph that suggests he used the Hitachi 55 amp with the ARS-5.

http://forums.sbo.sailboatowners.com/showthread.php?t=154754&#post1045103

Hello Below · Mar 31, 2015

Ralph Johnstone said:
Battery monitor shows that several hours of motoring and I'm back to 100% SOC.

Battery Monitors sometime fib a little. For example my Victron 600 manual states:

"The BMV resets to “fully charged” when the following “charged parameters” are met: the voltage exceeds 13.2 V and simultaneously the (tail-) charge current is less than 4.0 % of the total battery capacity (e.g. 8 A for a 200 Ah battery) during 4 minutes."

So in my case with a 464 Ah house bank, the Victron SOC jumped to 100% when the voltage exceeded 13.2V (always when under charge) and current was less than 18.56 A. A long way from fully charged especially when my previous stock Hitachi (80 amp) was in the chargers position.

Stu Jackson · Mar 31, 2015

Battery Monitors & Default Re-Programming

Len,

You might have seen this before:

For everyone installing a battery monitor: The "Gotcha Algorithm" thread, a "MUST READ"

http://c34.org/bbs/index.php/topic,4922.0.html

DEFAULTS are factory settings that are made to be modified to suit your setup.

Maine Sail has a much shorter description, but I don't have a link to it, might be in his battery monitor writeup on pbase.com

Stu Jackson · Mar 31, 2015

Great find! Ain't LINKS great?!? :dance:

Hello Below said:
Found an old post from Ralph that suggests he used the Hitachi 55 amp with the ARS-5.

http://forums.sbo.sailboatowners.com/showthread.php?t=154754&#post1045103

Hello Below · Mar 31, 2015

Stu Jackson said:
Len,

You might have seen this before:

For everyone installing a battery monitor: The "Gotcha Algorithm" thread, a "MUST READ"

http://c34.org/bbs/index.php/topic,4922.0.html

DEFAULTS are factory settings that are made to be modified to suit your setup.

Maine Sail has a much shorter description, but I don't have a link to it, might be in his battery monitor writeup on pbase.com

Thanks Stu. I had in fact recently read the post but took no action regarding it (forgot to write it down on my ToDo list and got busy on other projects.). You have just reminded me that I need to do some serious adjustin' with my battery monitor settings in line with the post.

woodster · Mar 31, 2015

Hello Below said:
Found an old post from Ralph that suggests he used the Hitachi 55 amp with the ARS-5.

http://forums.sbo.sailboatowners.com/showthread.php?t=154754&#post1045103

thanks HB.....i am still wondering if he converted the hatchie alt to external or did he just hook up the balmar without changing the alt to external regulator