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sjacovino 02-26-2002 01:03 PM

Internal Regulation
I recently repowered with a new Yanmar 3GM which came with an internally regulated Hitachi 80amp alternator. The problem is that it puts out 14.4 volts, which over time, I hear, will fry my gel cell batteries. My old engine/alternator had external regulation which put out 13.8 volts, more in line with that recommended for gel batteries.

My question is this: Is there a simple inexpensive way to step down the voltage by adding resistance on the battery side of the alternator? I''m not wild about the idea of having my new alternator modified by a shop and/or spending money on new wet cell batteries, new alternator and/or a smart regulation system. My cruising consists mostly of weekends and an occasional week or two of vacation time, the rest of the time my boat sits on a mooring with all power off (except the bilge pump of course). I have very modest electrical usage, so I''d like to keep things simple and inexpensive.

In ‘This Old Boat’, Don Casey talks about a disconnect switch between the alternator and battery, I’m guessing why not a resistor? All comments welcome.


kimberlite 02-26-2002 06:36 PM

Internal Regulation
YOU are going to kill your batteries.
I would have the alternator modified by an alternator shop and have THEM put on an external regulator. total cost $100-130.

sailnby 02-28-2002 07:31 PM

Internal Regulation
Current limiting is the real concern with a gel cell. Highest current influx is during the bulk charge period, limited to whatever the manufacturer specifies. Around 80% of full charge current needs to start dropping as battery voltage comes up. Without a regulator you would need to charge the battery to 12.4~12.6 volts, then throw the disconnect switch. It would be hard on the gel but not nearly as bad as charging to 13 volts with 80 amps... Greg

sjacovino 03-01-2002 06:05 AM

Internal Regulation
Hi Greg,

Maybe I''m not understanding you but... I do have a regulator, it''s just internal to the alternator. So far my best option seems to be having the alternator modified by a shop to support an external regulator that puts out a max of 13.8 volts. I was curious to know if a resistor could be used (external to the alt/reg unit)to step down the voltage from my existing regulator from 14.4 to 13.8 volts.


sailnby 03-01-2002 11:53 AM

Internal Regulation
A resistor can reduce voltage. The formula R=E/I (R ohms,E voltage,I amps)determines some static value for R. The only constant value in a charging scenario is voltage, making a resistor no good. A diode could work however. Are you sure the Hitachi doesn''t have jumpers or taps to adjust the output V? Is a good source of info that might help.

sjacovino 03-01-2002 04:47 PM

Internal Regulation
Thanks for the info.

No, I''m not sure the Hitachi doesn''t have some means of setting the voltage, I just don''t see anything obvious. I''m taking the Mack Boring Diesel course in a couple of weeks and since they are the ones that supplied this alternator I assume someone there must know something about it.
In the mean time I''ll check out the URL you recommend.

If this gets too crazy I think I''ll just have an alternator shop modify it for an external regulator.

Thanks again,

Peter_pan 03-16-2002 06:53 AM

Internal Regulation
Whoa Folks
I''m a charging system expert. 14.4 volts will not damage the batteries. It is the ideal limit and will maintain the batteries at full charge. What fries batteries is lack of maintinance. The water level must be maintained and should be checked regularly.(i.e. once a month.)
Jim ASE Certified Master Tech.

Peter_pan 03-16-2002 06:55 AM

Internal Regulation
Foot note.
What will fry the gel cells is being constantly charged by a shore power charger left on 7-24''s

sailnby 03-17-2002 04:29 PM

Internal Regulation
Hi Jim,
Would you agree with the following?
Gelled batteries: They must be charged at a slower rate (C/20) to prevent excess gas from damaging the cells. Current must be limited. Other disadvantages of gel cells is that they must be charged at a lower voltage (2/10th''s less) than flooded or AGM batteries. If overcharged, voids can develop in the gel which will never heal, causing a loss in battery capacity. (from Marine Batt Page). My system (reg/chrgr)uses three stages to charge my gels. I noticed that its voltage output was less when set for gel batts, which kind of matches what the battery page mentioned. I am less interested in the science as compared to (especially an experts) experience. Any suggestions what we can do to extend the life of our gel cells?

clayton 03-18-2002 05:42 AM

Internal Regulation
I agree with the tech- 14 volts will not kill your batteries. I suggest you contact the people at Ample Power in WA. THey have two excellent books on 12 volt systems and can advise you on how to get the most from your system.

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