Battery Charging Question

[motion30]

If starting with fully charged batteries and then using a total of 100 amps, how many amps would the charge source need to put back to fully charge the batteries again. In other words What are the losses?

[Sailmonkey]

It depends......a rough guess on my part is 130-150.....it's the last bit that's the doozy.


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[Ribbit]

Best to bank on about 50% more than taken out, when designing the system.

[motion30]

Ok 50% loss due to whatever inefficiency Exist

[smac999]

I think agms are better then flooded for this.


also I think you mean AH not amps...

[MarkSF]

Originally Posted by motion30

Ok 50% loss due to whatever inefficiency Exist

No, that's a 33 percent loss.

[BriaF]

When charging you battery HOW do you know if it is full or not
Undercharged or overcharged ??????????
Voltage alone is not a reliable indicator unless you can
rest you battery.
This is not realistically possible when you live aboard.
I have been living aboard for 15yrs & never really new if
my batteries were fully charged or not.

I now have a smartgauge & know when fully charged.
The smartgauge is a very valuable piece of equipment
& I would not be without it ever again.

My batteries are 8yrs old & still going strong expect them
to last at least another 2yrs +
This tool will allow you to get the best out of your batteries
You will know the depth of discharge & when full.

I typically discharge my batteries to 80% charge or less.
So I expect maximum life out of them ie. 3000 plus cycles
They are fullriver agm , total bank size 480 ah

[StuM]

Here we go again. You don't use 100 Amps. You use 100 Amp hrs

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[twinboat]

Yup , you use 100 AH. Then you put back 100 AH.

If you draw 100 amps in an hour ( 100 AH ), and you charge at 100 amp for an hour, you did not put it all back.

At different states of charge, batteries accept AH at different rates. The closer to full charge, the slower they return.

[botanybay]

Originally Posted by motion30

If starting with fully charged batteries and then using a total of 100 amps, how many amps would the charge source need to put back to fully charge the batteries again. In other words What are the losses?

Well, I happen to be sitting over at Catalina Island charging batteries at the moment and asked the BMV702s what they claim for the total number of kWh of energy removed from the batteries over the last 20 cycles vs the total amount of energy used to charge them. Note that there are periodic equalization cycles included in these numbers, a charge to completely charged at the dock, periodic acceptance charging when sitting at the dock. The batteries have been installed for about 18 months now (2 seasons) and are a bank of 6V golf cart batteries in two banks of 24V and are generally paralleled

Bank 1: 156 kWh total consumption / 191 kWh total charge = 81.7% efficient
Bank 2: 153 kWh total consumption / 197 kWh total charge = 77.7% efficient

Note that bank 2 has required a bit of additional care and feeding as it has one cell which had trouble coming into balance initially. I have been continuing to monitor but that gives two banks basically getting run in parallel almost all of the time.

So, I would expect somewhere between 20% and 30% additional charge being needed in my installation, so take out 100ah you will need to return between 120ah and 130ah to charge the battery.

David

[StuM]

David is dead right, but as others have pointed out, don't assume that a 40 Amp alternator will continue to put 40 anps back into you batteries. As they get closer to full they don't accept charge at the same rate. So while you may put 40 of your required Ah back in the first hour, the number of Ah you can put back in the last hour will be a lot less. IOW don't expect to replace your consumed 100 Ah in 3 hours (a theoretical 120 Ah input). It will take a lot longer than that.

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[Stu Jackson]

StuM and twinboat are right.

It is called battery acceptance.

It works like this:

Battery Acceptance by Stu Battery Acceptance

Why Going Into FLOAT is NOT Full

Why Going to Float is NOT Full

[motion30]

I guess I'm trying to do a little reverse engineering information wise. My solar controller tells me How many amp hours it has produce in a day I was just trying to get an approximation of how many amp Hr I have used in a day. I have used hydrometer to approximate my state of charge. I am getting full charge and a day

[Stu Jackson]

Originally Posted by motion30

........ I was just trying to get an approximation of how many amp Hr I have used in a day.

In the acceptance link, I mentioned that my energy budget is right on. Figuring what goes out is easier than what's coming back in.

You could also get a Victron battery monitor.

[motion30]

Yes.
I could get a battery monitor . I had one on my last boat and it was very helpful. The problem is on this boat there are 6 Pairs of 6 volt batteries . they are placed all over the bilge and it seems like each set has taps coming off of it. it's going to take a major rewire to be ever to use a single shunt. I would like to eventually do that but it will not happen right now.