Chargers

[MAKANA]

I recently switched all 8 batteries on my 1978 MY to AGM'S. I am still using the original 1978 Sentry charger. At a presentation recently a speaker who was supposed to be an expert said I should buy a new charger (he sells them). I really question his expertise as he also told me that my charger does not turn off when batteries are fully charged. I believe it does as when the meter goes to zero it quits humming. Will appreciate your advice as to whether I have to buy a new charger.

 

[Pete]

You just spent a good sum of money on 8 AGM batteries. Every manufacturer of AGM's can provide specific Bulk/Absorption/Float voltages to maximize the life and performance of the batteries. The optimum voltage varies by temperature, so you want a charger with a battery temperature sensor. The only way to get the battery life you paid for is to get a really good charger to take care of them.

The original Sentry charger is a single voltage charger. It monitors the voltage of one battery/battery bank and when the voltage drops to a predetermined level, it turns on and charges until the set voltage is reached (usually around 14.2 or so) at which time it shuts off and does nothing until the battery with the sensor drops back in voltage and causes the charger to start again. When this charger was designed, the marine market did not have AGM batteries.

My advice is quickly replace your charger with one that has at least the following features:

Functions as specified down to at least 100 volts AC, assuming it is a 120 volt charger.

Senses each of your battery banks separately, and charges each individually.

Has a battery temperature sensor that goes on at least one battery

Has adjustable Bulk/Absorption/Float voltages

It will pay for itself in battery life and battery capacity.

Pete

 

[GJH]

This is for a 32 volt system, correct? Pete is right, but the issue is finding a "smart" 32v charger. Major Power/Analytic Systems seem to be the only folks on the market with these; hard to find though I think you can order them direct through Major

http://www.majorpower.com/chargers/majorbca.html
http://www.analyticsystems.com/Products/BCA/bca1000.html

According to Mike P, NewMar discontinued theirs awhile ago.

 

[MikeP]

Yes, I ran into this same issue (smart charger for 32v) a while back. My solution was to utilize the Outback 3232 inverter/charger to charge the 32v batt banks.

The charger incorporated into the unit is extremely smart and can be custom talored for any voltage for the various charging levels - bulk/absorb/float/eq in .1v increments. Works marvelously and will completely charge both batt banks from 50% to full charge in a fraction of the time of the oem charger.

The down side is that it does not have separate outputs for each bank so the banks must be combined into one big bank. Actually, I have found that this works just fine and all related info (Calder, etc) on this states that one larger bank is considerably more efficient/batts last longer than two smaller banks that total the same size.

However, by combining it would be possible to drain the combined bank to the point where the starter(s) would have insufficient voltage. We spend a lot of time in our cruising on the hook and have never had the slightest difficulty but it is possible.

Our replacement NL genny uses 12v to start so we have a separate source to charge the batts in the unlikely event that we drain the mains so much that they won't start the engines. If our genny also used the mains to start, as per oem, I would probably be less inclined to combined the main batt banks though it depends a lot on where you cruise.

Frankly, in the Chesapeake, I wouldn't worry about it much. In more remote areas or offshore, I would want the banks separate for piece of mind if the genny started using the main batt banks.

 

[MAKANA]

Thanks to all for your answers to my query. They were very helpfull.
Looks like a new charger is in order.

John N

 

[SKYCHENEY]

Where did you find 8v AGM's?

 

[REBrueckner]

There must be an effect of different charge patterns and slightly different voltages since modern smart chargers offer selection buttons between sealed, wet and AGM. Although difficult to quantify, I'd also go for a smart charger with "AGM" selection capability. I don't know of any ferroresonant chargers that actually shut off; hum disappears anyway because at lower power/low charge not much is happening.

You can always leave the old charger on board as an emergency backup. Better to charge a battery imperfectly than let it go to a high percentage discharge. You'll also find modern smart chargers charge a LOT faster than older ferroresonant chargers. So if you run your genny to charge batts, you can explain to the admiral the new charger will reduce genny run time when at anchor!!! Also your new AGM's will accept four times the charge rate of older wet cell lead acid: If they are 220 amp hours you would be able to charge at 220 amps!!! whereas an older wet cell might take only about 50 amps or so....and charging is more efficient because AGM internal resistance is significantly lower than wet cell...so maybe 95% to 98% of your charge goes to to charge versus perhaps 75% to 80% for wet cell...