Guest Ferroresonant Battery Charger

[Ken Juul]

It's about time for me to buy new batteries.  Want to make sure my current charger won't fry them.  I have a Guest model 2520C, but no technical information.  Customer Service say's after about 80% charge it reduces to a trickle to finish topping the battery.  But that is what I would expect to hear from them.  They said they would mail the manuals, but while I wait does anyone have experience with Guest chargers?

[jentine]

I have used Guest chargers on several boats.  I currently have one on my power boat.  I have had it for five years and have not fried a battery yet.  If I did cook a battery, it would be my fault, not that of the charger.  A little common sense goes a long way.  I have a ferroresonant charger on my "34" and have had it since 1993 without any difficulty.  I, however, don't rely on the charger for continuous battery charge maintenance.  I do not leave the charger plugged in when I leave for the week.  IMHO battery chargers are only for topping off or shock therapy.  For charge maintenance, I use solar chargers - free juice, reliable regulation.

[Jim Moe]

Guest makes a number of different chargers, most of which are either SCR or switchers and fall into the category of "smart" three-stage units.  However ferro-resonant chargers have a nasty characteristic of putting out a very high voltage when the load is very low - like with a fully charged or nearly full battery.  This voltage can dry out a flooded lead-acid battery and shorten its life but it can rapidly kill a gel cell or AGM battery.  Consequently, it's not a good idea for marine application.

I've a few patents on regulated chargers and one on regulating a ferro since all railroad signal installations have a 12 volt battery backup and I've been in that business for 30 plus years.  If you do keep your ferro, watch your battery voltage and/or current and get it off line soon as the battery is charged.

[Stu Jackson]

One way to get it off line, as Jim suggests, is simply using a timer on the charger.  Ron recommended having it run only one or two hours a day, to avoid overcharging.  Simple, and sure cheaper than new batteries.

Stu

[Ted Pounds]

The problem with Stu's suggestion is the batteries never get fully charged.  They're only charged through the "bulk" stage.  That will also wear down batteries; albeit slower than "drying them out".  Jim Kane solves that problem by using solar power for the "absorption" phase and bringing them up to full charge.  Since juice is free at my marina I found the Statpower Truecharge is the way to go for me here in the Great White North.  :cool:

Ted

[Stu Jackson]

Ted,

Ferroresonant chargers do not have any stages, that's the problem with them.

The only way to avoid these "constant voltage - reducing amp" chargers from burning off the water in the battery's cells is to turn them off.  That's hard for people who leave their boats unattended and plugged in all week.  That was the idea.

I just "rekindled" this thread because of recent discussions about batteries and chargers.

www.amplepower.com is a great source of battery charging information.

Stu

[Ted Pounds]

I realize ferro's don't have stages.  I just meant that they're analogous to the bulk stage of a 3-stage.  My point is that by turning off the Ferrorsonant charger to avoid frying the batteries you're left with only about 80% charged batteries, which, while not as bad a burning off the water, is  still not not good for them.

Ted

[Stu Jackson]

Ted, I agree.

Which is simply a great way of saying get rid of your old ferro charger.

Stu