Charger question

[billwilletts]

So my Sentry charger is set up to cut off at 36 volts. I am having to add water every 3 months to keep them topped off sufficiently. I am wondering if this is too high. Thinking about cutting it back to 34 volts cut out?

 

[Reefgeorge]

So my Sentry charger is set up to cut off at 36 volts. I am having to add water every 3 months to keep them topped off sufficiently. I am wondering if this is too high. Thinking about cutting it back to 34 volts cut out?

What do you mean by "cut off"? A charger should go through a 3 stage cycle: Bulk, absorbtion, and float which are 3 different charging levels - a combination of constant current and constant voltage. The charger then stays in float indefinitely. There are other parameters in a sophisticatec charger such as minimum times in the first stages. The voltage levels should be varied by battery temperature so there is no one value.

 

[GJH]

You need to make sure it actually is cutting off there and test it's output. It is adjustable.
Check the manual.
Three months is not so bad though, how old are the batteries?

 

[billwilletts]

It's a regular Sentry charger. It cuts out, floats, stops charging at 36v. Is 4 volts above 32 too much and making the batteries lose water too quick? I have new Rolls batteries-- about 6000 bucks worth and I'm trying to take good care of them. I'm wondering if 34v would be easier on the batteries.

 

[Reefgeorge]

If you want to take the best care of your batteries:

Get the charging specs for your exact battery model/technology, they vary

Program the absorption and float voltages according to the battery specs. Really sophisticated Chargers also have minimum times at each stage which help extend battery life. With batteries that cost $6K a modern high end charger may be in order. It’s constant current in bulk charging until the absorption voltage is met and the minimum time is met, absorption voltage/time, then float voltage indefinitely, unless the charger current output is exceeded and the battery voltage drops, then back up to bulk/absorption voltage

Install the temp probe option for your charger, the correct charging voltages vary with temperature quite a bit at the extremes. A good charger will also shut down on a high temp fault so one shorted cell does not result in a total loss

Both overcharging and under charging reduce battery life

Some batteries recommend a routine equalization algorithm for maximum life which is a higher than normal charge or a pulsing high charge for a certain interval

So this charger shuts off at some point and does not leave a float voltage on the batteries (cuts out)? I would again, refer to the battery manufacturer for their ideal charging specs/routine.

 

[Reefgeorge]

It's a regular Sentry charger. It cuts out, floats, stops charging at 36v. Is 4 volts above 32 too much and making the batteries lose water too quick? I have new Rolls batteries-- about 6000 bucks worth and I'm trying to take good care of them. I'm wondering if 34v would be easier on the batteries.

The correct charging voltages vary with temperature and battery technology as well as mnfg preferences. The correct float voltage has a range of around 34-38 volts.

 

[billwilletts]

I was reading the Sentry specs and they recommend for flooded batteries a cut out at 38v which I think is where mine is set. If I use the 2.2v per cell that Rolls recommends that would be a tad over 35 volts. (16 cells in a 32v system). So i think I might set mine to 36 and split the difference? What do you think George?

Its a Sentry FR system. A good charger but not that sophisticated.

http://www.sentrychargers.com/downloads/FR_Series_Battery_Charger_Manual_booklet_Dec_2017.pdf

 

[Reefgeorge]

I would go with however the battery mnfg wants their batteries charged. I see that this charger literally turns off and makes no mention of a three stage charging algorithm. It also has no provision for a temp probe in the battery box. The 2.2V per cell that Rolls specs is probably at room temp. If your battery box is routinely hotter than that then you will still be overcharging because the charger won’t debate for temperature. Conversely, you will undercharge in cold weather which is also bad. Given your very large investment in batteries I would consider a modern charger. brands mentioned here and held in high regard are Victron, Mastervolt, Newport and Outback (may be only inverters).

 

[scottinsydney]

Analytic Systems built a military grade 32 volt 30 amp 2 bank automatic Charger for me a couple of years ago. This replaced an older ferro type Sentry. The new charger has a nice digital display large enuf for me to read from the engine room door and a couple of different programs. My boat is on a swing mooring so it’s obviously not possible to have trickle charging. (A 32 volt solar panel system does the trickle charging when the boat is not being used.). The AS also has a function suited to Genset charging which is great when we are cruising.Analytic Systems website is at www.analyticsystems.com