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The investment makes sense if you are adding to the house bank but not for a single group 27. At around 100 AH give or take it will only accept 25 amps in bulk anyway. The last 15% of will take many hours with any alternator.
 

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Still, the bigger alternator might be giving him twice the output at "idle" speed. There's a lot to be gained from that as well, where most alternators can't wake up enough to do any work until cruising speed. Can't assume the pulley ratios and output-vs-speed ranges have been matched up even on a production boat.
 

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Discussion Starter · #4 ·
The point is to recharge the battery quickly, daily. The Balmar puts out about 80 initial amps when the battery is discharged to 60 percent. It returns the battery to 80 percent charge in 35-40 minutes at the cost of a quarter-gallon fuel.

No need to recharge the last 15 or 20 percent, you stop when the input drops to somewhere around 25 amps. The only time my batteries are at 100 percent is at the dock with the charger plugged in.
 

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"discharged to 60 percent. It returns the battery to 80 percent"
So you are only using 20% of the rated battery capacity, instead of a typical (on paper) 50%.

"charge in 35-40 minutes at the cost of a quarter-gallon fuel."
Which is a good thing, but because of
"No need to recharge the last 15 or 20 percent,"
you're now going to be running the engine and charging twice as often. And running out of power twice as often, which may mean keeping someone awake by running the engine while they're off watch.

There's also another reason not to do this: Most of the wear on engines, any engines, comes from startup and shutdown. The starter and alternator are spiked and stressed both times. The engine is not fully lubricated during starts, and if not properly cooled the oil may be coking on the valve covers, etc. after shutdowns. These are the reasons that many fleet operators tell their drivers to leave the engine running all day, and not shut it down during short stops. We may talk of how many hours an engine has between overhauls, but "hours" may mean less than "how many startups?" it has. Certainly, the life of the starter now gets cut in half as well.

So it is nice if you've got the capacity to run that way (ignoring any questions about what's best for the batteries) but there's an extra cost to that, too.
 

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Discussion Starter · #6 · (Edited)
My procedures are fairly standard for the stated needs. Let me explain again.

I use 20 amp hours a day offshore. The point of the larger alternator is to quickly regain the 20 amps.

I run the engine once a day for 35 minutes. I suppose I could run it every second or third day for an hour or more, but one likes to keep topped up in case of unusual needs.

The notion that it is hard on engines to run them once a day while cruising is new to me.

Cheers,
CW
 

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$815!:eek:

I replaced the Motorola 51 Amp alternator on my M25 with a Leece-Nevil 90 Amp alternator for ~$200... No, it does not have a smart regulator. But, I think an ARS-5 can be had for less than $600 ($300 is more like it).
 
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My procedures are fairly standard for the stated needs. Let me explain again.

I use 20 amp hours a day offshore. The point of the larger alternator is to quickly regain the 20 amps.

I run the engine once a day for 35 minutes. I suppose I could run it every second or third day for an hour or more, but one likes to keep topped up in case of unusual needs.

The notion that it is hard on engines to run them once a day while cruising is new to me.

Cheers,
CW
See post #2

A single group 27 battery - 100 AH at most - will not accept more than 25 amps of current, probably closer to 20 amps, no matter how large your alternator is and with any regulator.
 

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See post #2

A single group 27 battery - 100 AH at most - will not accept more than 25 amps of current, probably closer to 20 amps, no matter how large your alternator is and with any regulator.
It will accept more during the in-rush but not for very long before it hits the limiting voltage. This is actually an inefficient way to get the most current into a flooded battery as it really tends to build a surface charge and not penetrate the plates adequately.

That said there are benefits to external regulation and a better alt even on a small battery bank but they should always be balanced against your own personal budget. If it makes Christian happy that is all that matters..

#1 If voltage sensing is wired properly, and the Balmar manual is WRONG about how to wire these regulators, then the benefits over a self sensed alt can mean significantly faster bulk charging and early absorption charging.

#2 A remote temp sensor can be used to provide the proper charging voltage for the batteries actual temp.

#3 Voltage adjustments can be made to get the most into the battery the quickest. For example 14.8V for 20 minutes then a drop to 14.6V for the duration until the transition to float.

#4 Belt Manager/Current Limiting can be used to set the alt up to provide the most current with the least belt dust.



I am currently involved in some partial state of charge testing (PSOC) which will eventually be published. Sadly it is a long process and at least a year out.....

So far the data has been eye opening to say the least and some new lead acid technologies have really made great strides and another one is due out in January so we are waiting for that test battery as well...

What has been the most eye opening is that batteries drop off quickly in usable Ah capacity under PSOC operation... So the 1 hour a day charging you do may start out at 50 usable Ah's and within 10 days you may have lost 25% of that usable capacity or more with the same time spent charging each day.:eek:
 

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Once again, Christian, very well written.. :)
 
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