How long to charge a battery?

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fshrvmn

fshrvmn

Active member
Joined
May 4, 2009
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Location
Idaho Falls
Hi Folks!
I'd like to know roughly how long it would take to charge a group 24 battery that has been discharged 50% and that is being charged with a 15 amp charger (open and closed circuit)?

Also, I would be using a genny with an 8 amp DC output to re-charge the charger and need to know if I am supposed to connect the genny to the charger while charging the battery or not?  I am a neophyte when it comes to all of this battery and genny stuff, but hope to rise to the status of educated-novice before dry camping this season.

Thanks, Mike
 
A typical group 24 battery is about 80-85 amp hours, so 50% charge means it needs 40+ AH pumped back in. You would think a 15 amp charger would do it in 3 hours, but batteries don't work that way. When they are well discharged they will accept 12-15 amps from a 15 amp charger, but as the charge comes up the rate of acceptance slows down and the charge rate drops off quickly to 5A or less. I would figure at least 8 hours to get to 90% charge and probably 10-12 to get back to 100%.  When RVers spend several days with the genny, they are usually oscillating between 50% charge and 80% charge because nobody wants to run the genset long enough to get to 100%.

Do NOT connect the genset DC output to the pop-up's charger!  The charger runs on 120vac, not DC. You can charge by connecting the genset DC output direct to the battery, or you can charge by plugging the converter/charger power source to the genset 120vac output.  When you plug the trailer into the genset 120vac outlet, the onbaord converter/charger will receive power and automatically start charging the batetry. You don't need to do anything else.
 
That DC out on the genny is usually a bad choice, But then I don't know what your options are.

1: No regulation means good chance of overcharge
2: Low current means it takes a long time to charge (See Ron's post for an idea of how long)

A better choice is to feed 120vac to a proper 3-stage converter/charger,,, There are several makes and models on the market,
 
Gary and John,

After reading your posts I did some additional research and found out that my converter/charger is NOT multi-stage.  Therefore, I just purchased the Centurion 3000 xl upgrade board for my existing Centurion.  The upgrade IS multi-stage and delivers 30amps during intial-stage charging (12 amps on the old board).  This should do the trick when connected to a Honda eu1000 or 2000 genny.  Now I have to decide on the genny to purchase!

Thank you both very much for helping things to make much more sense.  ;)

Mike
 
John From Detroit said:
That DC out on the genny is usually a bad choice, But then I don't know what your options are.

1: No regulation means good chance of overcharge
2: Low current means it takes a long time to charge (See Ron's post for an idea of how long)

A better choice is to feed 120vac to a proper 3-stage converter/charger,,, There are several makes and models on the market,
Click to expand...

How much is a proper 3-stage charger? 

I just bought this charger: Eliminator Battery Charger

It's a so-called intelligent charger.  I displays the voltage sent to the battery and I see it in the high 14V when it starts and lowers down as the charge goes up.  It's a 15/2A charger.  Once it reaches 100%, it toggles to trickle charge.

It took one hour to charge my group 24 from 80% to 100%.  Once charged, I disconnected it.  3 days later, I checked it with the multimeter and the voltage was 12.7V, so still full charge.

My plan was to use that on the genset to charge my battery when boondocking.  Seems a lot faster then my built-in converter/charger.  But I figure if it's fast, there ought to be a drawback.
 
Marc,

The upgrade I purchased set me back $120 (the Centurion CS 3000 Replacement).


The smart charger I was looking at previously with half the DC amp output was the Schauer JAC1212 $100.

Mike
 
Automotive style "Smart" chargers are usually two stage at best. Basically they start out at a constant amp rate and pushes it til the battery is nearly full charge  and then  shifts to a float (trickle) mode. I couldn't tell from the Eliminator specs what methods of regulation it uses, so anything I said would be conjecture.

A three stage charger use a constant amp rate for a while (bulk charge) and then switches to constant voltage with a tapering amp rate (acceptance charge ) and then finishes with float mode. This keeps the charger in tune with the abtteries ability to accept charging.
To learn more about the differences, see http://www.donrowe.com/battery_charger/samlex_document.html
 
The Centurion 3000 Upgrade ought to speed your charging quite a bit. You still have the problem if getting from 80% charge to 100%, though. Once the battery reaches about 80% of capacity, it simply won't accept electricity at more than a trickle.
 
Gary,

You mentioned in a previous post on my thread that most dry-camp RVers use their gennys to bring their batteries up to about 80% and then draw back down to 50% to minimize recharge time with the genny (for me hopefully only 2-3 hours).  I would like to do the same thing for up to five days (with the primary draw down occurring over night with the electric fan on the heater).  I would then plan on plugging into 110 v once home and bring the battery up to 100% on stage three.  Any potential problems with this plan?

Mike
 
fshrvmn said:
Gary,

You mentioned in a previous post on my thread that most dry-camp RVers use their gennys to bring their batteries up to about 80% and then draw back down to 50% to minimize recharge time with the genny (for me hopefully only 2-3 hours).  I would like to do the same thing for up to five days (with the primary draw down occurring over night with the electric fan on the heater).  I would then plan on plugging into 110 v once home and bring the battery up to 100% on stage three.  Any potential problems with this plan?

Mike
Click to expand...

Worked for me for 6 weeks this winter.  Rare use of furnace. Normally ran genny for about an hour mid day when the voltage fell to 12.2.  Then a couple of hours at night while we did supper & TV.  Repeat until time to go home.

Joel
 
I would then plan on plugging into 110 v once home and bring the battery up to 100% on stage three.  Any potential problems with this plan?
Click to expand...

Nope, none at all. 50% charge is equivalent to about 12.0v in an open circuit measurement (no load on battery) or around 11.7-11.8v with modest load running. 80% is about 12.5v unloaded and a bit less with a load. Measurements are made with the charger OFF.

There is a battery charge table somewhere in the forum library. It shows percentage of charge vs voltage and specific gravity.
 
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