# Charging current of 20 AH Battery

Discussion in 'The Projects Forum' started by kfrazie1, Jan 6, 2010.

1. ### kfrazie1 Thread Starter New Member

Jan 4, 2010
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0
Using a 0 - 24 volt DC motor to charge a 20 AH lead acid battery through a charge controller. Battery is charging around 14.5 Volts. Trying to determine the current on the motor created by charging the battery. Motor can not exceed 14 Amps. I think this has something to do with the state of charge of the battery. Any ideas?

2. ### SgtWookie Expert

Jul 17, 2007
22,199
1,801
I don't know why you're trying to charge a battery using a 0-24v DC motor.

Need more details about the charge controller.

Need more details about the battery. If it's a SLA type, 14.5v is probably too high.

3. ### R!f@@ AAC Fanatic!

Apr 2, 2009
9,652
1,110
A 14A Motor is more than enuf to charge a 20AH battery.
I believe you are in safe specs provided that u have properly rated (13.8V) lead acid battery charger

Rifaa

4. ### kfrazie1 Thread Starter New Member

Jan 4, 2010
23
0
Its a "pedal power generator". Same thread I made earlier but I'm gonna use a battery instead of a capacitor. Not sure what the exact charging voltage of the battery is, easy enough to figure out.

The charge controller : http://www.pedalpowergenerator.com/docs/nc25a_manual.pdf

I really havn't chosen an exact battery yet because I need to know what type of battery is going to draw too much current (>14 Amps) from the DC motor I'm using. I have been looking at deep cycle and lead acid batteries at relatively low AH and now I'm trying to determine the current draw.

Thanks for the input

5. ### SgtWookie Expert

Jul 17, 2007
22,199
1,801
R!f@@,
What you posted is not true.

We do not have the specifications for the battery or the charge controller.

I think that our OP has simply thrown together a number of components, and is hoping they will work.

A 20AH battery should not be charged faster than 1/5 it's AH rating, or 4A. Otherwise, the battery may become overheated internally, and vent its' contents. This will damage or destroy the battery.

Charging efficiency will be around 70% to 80% for a SLA battery.

The battery should be charged at a constant current to a voltage recommended by the manufacturer's datasheet - for the bulk charge rate.

Then the battery should be charged at a constant voltage until the charge current decreases to the rate specified in the manufacturers' datasheet.

Then the battery should be "float charged" at a voltage dependent on the battery internal temperature. This should also be specified in the manufacturers' datasheet.

6. ### kfrazie1 Thread Starter New Member

Jan 4, 2010
23
0
Edit: The motor is acting as a generator if that clears things up

I am aware of the method of charging and how much current batteries should be charged with based on their AH rating. I do not have any control over what current the motor puts out. I can only control the voltage produced by varying the pedaling speed. What I'm trying to figure out is what current the motor will "choose" to put out when charging the battery. For appliances this is simple. Without including efficiencies, I=P/V, for a 120 watt appliance at 12V the motor will put out about 10 amps, a safe level. Essentially I am trying to figure out what "load [watts]" the battery puts on the motor so I can determine the current going into the battery from the motor to ensure it doesnt overheat. Is this a function of the batteries internal resistance? or somehow regulated by the charge controller? or decrease with the SOC? I have no idea...I believe I read something that said a battery will draw as much current as it can, which will fry my motor.

Thanks again

Last edited: Jan 6, 2010
7. ### R!f@@ AAC Fanatic!

Apr 2, 2009
9,652
1,110
Hey SGT, I did not get you what u say it's not true.
I just said his motor should do fine provided he has a proper SLA charger.
I said the nominal charging should be at 13.8V, even sometimes they vary from 13.2 to 13.8.
I implied tht it is his charger the he should be worried about not the motor.
I believe I know how a SLA should be charged, having those types around me every now and then.
was I wrong ?

Rifaa

8. ### thyristor Active Member

Dec 27, 2009
94
0
Yes!!!

Sealed lead acids can be charged at up to 14.2v. (Bulk and absorption stages). They will charge much faster at this voltage than at 13.3v to 13.8v.

You only need to drop to around 13.4v in the float stage.

Wet lead acids can be charged at up to 14.8v in the B & A stages.

9. ### R!f@@ AAC Fanatic!

Apr 2, 2009
9,652
1,110
is that so.
now how come I did not see tht in chargers that I have used.
I have never seen a SLA charger putting out 14.2V.
I say this cause I have seen my share of dead UPS's.
They never exceed 13.8V.

am I missing something here.

Rifaa

10. ### thyristor Active Member

Dec 27, 2009
94
0
You've led a very sheltered life then and know little about lead acid batteries IMHO.

Take a look here for example...

I can give you any number of other charger web sites that say the same.

Here's a quote from the pdf I highlighted.

"Before switching on the charger it is important to set up the battery type. Please choose a battery type from below. The highest charge rate (and voltage) will be the open lead-acid (set to 14.8V on high charge), then sealed lead-acid and AGM (14.4V, then gel (14.1V-14.4V). (The AGM and gel voltages tend to vary from company to company so check which voltage your batteries require)."

11. ### R!f@@ AAC Fanatic!

Apr 2, 2009
9,652
1,110
well what do you know?
you learn something knew every day.

You know sometimes I wonder why battery testers says after testing it, to charge the battery at 30A for 30 seconds. I wonder how we could do that without increasing the charge voltage.
Shouldn't the voltage be increased if you need to charge at high current?
If yes then by how much, for a typical SLA battery?
I did tried a battery once after testing it, I used a variable supply to give a high voltage but the current won't rise, may it be that the battery is sulphated?
If so will a good battery but heavily discharge one draw that amount of current and at what voltage will be if the battery is a 12V one (13.2V)?
Won't it be dangerous to increase the voltage more than 14.8V, if say the current does not rise at tht voltage but shows a significant amount of current increase above 14.8V or so?
These are a few questions that haunted me for some time, I never found any info on it much.
Care to high light me on this any one?

Rifaa

12. ### kfrazie1 Thread Starter New Member

Jan 4, 2010
23
0
So does anyone know how much current the battery will draw from the charge controller, which is connected to a DC motor that is being pedaled......