awol
Well-Known Member
Sorry, wasn't concentrating. Rugby (that's how it was advertised, anyway), beer and coherent thought don't go together.
2GM20 Alternator Upgrade?
- Thread starter KevO
- Start date
Sorry, wasn't concentrating. Rugby (that's how it was advertised, anyway), beer and coherent thought don't go together.
Maine Sail
Well-Known Member
With a machine sensed alternator, meaning it sense voltage at its own B+ terminal, there will still be voltage drop in the wire to the batteries unless you have very large cables. As the batteries approach full, and accepted current falls off, then the alt voltage and battery voltage will finally match. Throw a diode isolator on top of system voltage drops and it creates a nightmare for charging batteries.
The dirty little secret with many Hitachi alternators, like those on Yanmar engines, is that the "dumb" internal regulator is actually smarter than most "dumb" regulators. They don't just regulate voltage they also reduce voltage based on alternator temperature. So when these alts are used on large banks, and the alternator gets hot, the voltage is reduced by the regulator based on alternator temperature. Reducing the voltage also reduces the current to the battery, voltage is pressure, and allows the alternator to cool. This internal temp compensation is designed to protect the alternator from overheating and cooking itself.. Unfortunately it kills alternator output performance.
Last edited:
KevO
Well-Known Member
Ok, lots of info, some of it leading to even more confusion... my fault, not any of yours 
So... I think I'm gonna take up the offer of the 55amp alt, the price seems too good to miss. The Sterling alt to battery charger is quite a bit more dosh that I was hoping to spend but I suppose I could bite the bullet if it is genuinely the best solution. Is there an effective yet more financially attractive option?
I need to be able to fit it myself... especially if i'm looking at near £300 for the sterling!!!
Is it really that much more effective (and worth the extra dosh) than the Pro-Split R? http://www.sterling-power.com/products-prosplit.htm
So... I think I'm gonna take up the offer of the 55amp alt, the price seems too good to miss. The Sterling alt to battery charger is quite a bit more dosh that I was hoping to spend but I suppose I could bite the bullet if it is genuinely the best solution. Is there an effective yet more financially attractive option?
I need to be able to fit it myself... especially if i'm looking at near £300 for the sterling!!!
Is it really that much more effective (and worth the extra dosh) than the Pro-Split R? http://www.sterling-power.com/products-prosplit.htm
JimC
Well-Known Member
I would get the 55 amp alternator. If you don't like your 1-2-both switch replace it with a VSR. Beyond that I wouldn't be in a hurry to spend any more money. If your batteries are reading 12.65 volts or more across the terminals after 4 hours resting then they are being adequately charged IMHO.
xeitosaphil
Well-Known Member
Very interested in where you can get one from a dealer for £60.00 ? the cheapest I have seen is £130.00 in plymouth
KevO
Well-Known Member
Local dealer right outside my boatyard in Falmouth. I went in for a spare impeller and we just got chatting about alternators in general. He said he had a bunch of em (brand new but no longer being stocked) out the back and would see if he had one for a GM20. He did and we haggled
PM me phil and I'll see what I can do when I go down again later this week.
Last edited: