More Amps = Faster charging?

[Zillard]

Hi guys

I found a few threads about panels in series and parallel, and i started wondering about my question below. But the threads were form 2009, so didnt want to post on a dead thread, but I need confirmation on something that is bothering me, so please assist if you can.

Let say i have a panel/controller setup capable of charging a battery at for example 18V and 1A, and complete the charge cycle in 6 hours. If i put additional panels in parallel to up my current, and my new panel/controller configuration can charge at 18V and 6A, will my charge cycle complete in 1 hour instead of 6? Im sure if so, it wont be such a direct correlation, but just saying it for example. In essence, more Amps decreases charge time.

Am i correct with my above statement?

I have more questions, but will only ask them if i am correct in my assumptions.

Looking forward to your responses.

Thanks

[Sunking]

Yes that is correct, but there are limits as to how fast you can charge a battery.

From the formula you can see it in action. H = AH/A, A = AH/H, AH = A x H

[Mike90250]

At some point, the limits of the battery will apply, generally, it's around 10% of capacity, that you don't want to exceed, when charging. Otherwise, you overheat the battery and damage it. Even if it's only 0.5% each damage cycle, in a year (360 cycles) , that can add up. And that varys, when the battery is discharged , it's a little safer to charge it faster, but as it approaches 80%, you have to throttle back.

[Zillard]

@Sunking: Ok, i thought the AH rating was just how long it can sustain the rated current for. So it works the same for charging the battery? Need so many amps for so many hours to charge it.

@Mike: Not sure about your statement. Should i not exceed the rated amps by more than 10% of charging i.e if rated at 1A i shouldn't charge it with 1.1A?

OR, i can charge at as much amps as i can until i get to 90% of full capacity, then throttle down to normal amp rating?

I can see where a decent MPPT controller will be helpful in such a case.

[Sunking]

@Sunking: Ok, i thought the AH rating was just how long it can sustain the rated current for. So it works the same for charging the battery?

Yes minus efficiency. For charging it is A x H x 1.2

[Mike90250]

....OR, i can charge at as much amps as i can until i get to 90% of full capacity, then throttle down to normal amp rating?.....

1) I never said or hinted, "as much amps as you can", I said you can go a bit above the suggested, for a short time, while the battery is way low.

2) 90% is your own invention. I said 80% (of full), after that the charge rate has to slow down or the battery can/will boil. That's always bad.

[Zillard]

Thanks Mike. Now i know.

All the more important to get the correct charge controller to ensure the batteries dont boil.

Thanks guys for your input.

[sumonkhan44]

that you don't want to exceed, when charging. Otherwise, you overheat the battery and damage it. Even if it's only 0.5% each damage cycle, in a year (360 cycles) , that can add up. And that varys, when the battery is discharged , it's a little safer to charge it faster, but as it approaches 80%,

Mod note - Links are not allowed - you can post your email in your profile if you wish

[Sunking]

Thanks Mike. Now i know.

All the more important to get the correct charge controller to ensure the batteries dont boil.

Thanks guys for your input.

Zillard that is not exactly true. You want flooded lead acid batteries to bubble and churn a bit. For flooded lead acid batteries the highest charge rate is typically C/8 or 13% of the batteries rated 20 hour discharge rate Amp Hour capacity. So if you have a 100 AH 12 volt battery means you want to limit the highest charge current to 13 amps.

On the low side you do not want to go below C/20 or 5%.

To determine panel size to do that job depends on the charge controller type used. If you use a PWM charge then input current = output current. So using a standard 12 volt panel @ 13% you need the panel current to = 13 amps and that would require about a 210 watt panel.

For MPPT to find the panel wattage is easy. Watt = Volts x Amps. So with a 12 volt battery and 13 amps = 156 watts or round up to 160 watts.

[Zillard]

Thanks Sunking.

One more question. If i have a battery bank consisting of 10 x 100 Ah 12V batteries, wired in parralel, i would still just apply a charge of 13A to the bank? Or will i have to boost it to 130A which is 13% of the 1000 Ah capacity? I guess what im getting at is do i work on 13% of the bank capacity or the capacity of each battery in the bank?

Thanks in advance.

[Sunking]

Thanks Sunking.

One more question. If i have a battery bank consisting of 10 x 100 Ah 12V batteries, wired in parralel, i would still just apply a charge of 13A to the bank? Or will i have to boost it to 130A which is 13% of the 1000 Ah capacity? I guess what im getting at is do i work on 13% of the bank capacity or the capacity of each battery in the bank?

No for the entire bank, When you made it 10 batteries in parallel you made a 12 volt 1000 AH battery.

To be honest you are going to have a lot of problems with batteries in parallel keeping them all equalized. You will likely be replacing the batteries every year or two. The other problem you are going to have using 12 volts at that battery capacity you wil have to use at least 2, maybe 3, or more charge controllers.

[Zillard]

Ok, so would you recommend having a higher voltage battery then?

If you up the voltage, and lower the Ah capacity, will it decrease your charge time? My mind is realing now on all the questions i have, but will reasearch a bit more before i post something silly.

[Sunking]

Ok, so would you recommend having a higher voltage battery then?

If you up the voltage, and lower the Ah capacity, will it decrease your charge time? My mind is realing now on all the questions i have, but will reasearch a bit more before i post something silly.

Will not affect charge time at all.

with your 10 12 volt batteries in parallel you have a capacity of 12 volts x 1000 AH = 12,000 watt hours. To charge them at the C/10 rate, 100 amps would require 1200 watt panel. If you were to reconfigure the batteries all in series to 120 volts at 100 AH, Would still require a 1200 watt panel to generate a C/10 charge rate of 10 amps.

But to answer your question you should be using a higher battery voltage so you only require 1 charge controller. Problem is 10 batteries do not fit for 24 or 48 volts. With 10 batteris your only option is 24 volts or 5 parallel strings. That would allow you to use a 80 amp charge controller and allow a panel wattage up to 2000 watts. At 12 volts the most panel wattage you can have is 1000 watts with an 80 amp charge controller.

[shanthi]

mppt

does it mean an mppt technique

[ mod note - we won't accept attachments (especially PDF) from new users, till we have some idea of what the story is, a terse one liner is not enough to allow PDF's with all the nasty tricks that can come with them on un-patched computers. ] Expound more, in text, of what you are trying to say.

[Zillard]

Will not affect charge time at all.

with your 10 12 volt batteries in parallel you have a capacity of 12 volts x 1000 AH = 12,000 watt hours. To charge them at the C/10 rate, 100 amps would require 1200 watt panel. If you were to reconfigure the batteries all in series to 120 volts at 100 AH, Would still require a 1200 watt panel to generate a C/10 charge rate of 10 amps.

But to answer your question you should be using a higher battery voltage so you only require 1 charge controller. Problem is 10 batteries do not fit for 24 or 48 volts. With 10 batteris your only option is 24 volts or 5 parallel strings. That would allow you to use a 80 amp charge controller and allow a panel wattage up to 2000 watts. At 12 volts the most panel wattage you can have is 1000 watts with an 80 amp charge controller.

I see what you mean. Thanks Sunking. I am planning a small system to run my fridge off as a start, along with rewiring my apartments lights to run on 12V LEDs.

So in effect i would need to have a battery bank to sustain the fridge, and a seperate 12V battery to run the lights off. I think 1 should be sufficient, but will calculate the exact requirements to make sure.

I am limited to the amount of panels i can use, as i have a middle floor apartment, and we are not allowed to install anything on the roof. I will probably be able to install them on my balcony. This will however limit my exposure i know, so ill have to ensure my charging/battery capacity is enough.

Thanks again.