Constant voltage charge

inthejungle

I just wanted to ask if anyone is currently not using a traditional 3 stage charging and rather using a constant voltage charge on the FLA batteries?


I good friend of mine recently recommended maybe trying this with a bank of batteries we have, but wasn't sure about using it? Any one accomplished this with a out back charge controller?

Any thoughts?

westbranch

Re: Constant voltage charge

do you know the brand of charger your friend is using for constant V?

NorthGuy

Re: Constant voltage charge

In my eyes, the traditional method is constant voltage charge.

The only deviation is that after charge it drops to float, but I wouldn't change this.

Cariboocoot

Re: Constant voltage charge

Voltage changes during Bulk as the battery charges: V up, A down.
In Absorb stage the Voltage is stable as current drops off further.
In Float stage the Voltage is stable at a lower point and current varies according to load demand.

This is the standard operation for off-grid charge controllers.

Industrial (grid powered) chargers often do it the other way around, with a fixed current rate while Voltage rises. This usually isn't feasible off grid.

zoneblue

Re: Constant voltage charge

What are you trying to achieve, and with what gear, and why?

inthejungle

Re: Constant voltage charge

Thanks for everyone's initial thoughts,

Basically my equipment is this

3 245 Canadian Solar Panels for a total of 720w
FM 80
Rolls Batteries 350AH


I have been having a daily use of about 7% of my total capacity(measured by my battery monitor based on amps out and the battery monitor is calibrated based on my SG's),
so I usually will only charge every two days to start the charge at 80% SOC. I do this by manually shutting down the breaker on the PV array.

A buddy of mine recently wrote me and explained that he might try to "another option for charging is to disable the 3-stage charging and use a
constant voltage charge. This works fine all the time in all kinds of equipment, including cars. See if there's a way to disable the 3-stage charging, or
set the charging voltages/options to the equivalent of a constant voltage charge."

This was his thoughts, my thoughts were I wonder if I could setup the outback FM 80 to do an equalization charge every two days, voltage, time, and current equals a constant voltage charge. If I wanted to I could even setup the outback charger to output a max amp so I would know, max amps input, max voltage and max time

Just wondering what people thoughts would be on doing something like this?

zoneblue

Re: Constant voltage charge

We recently had a large wonder along these lines here:

http://forum.solar-electric.com/showthread.php?20840-What-is-the-optimal-SOC-range-for-cycling-lead-acid-batteries&highlight=optimum+battery+charge

To me this idea of not fully charging batterys is a tradeoff betwen extended life, and requireing a bigger bank to make it work, due to the reduced reserve capacity.

There is of course nothing to stop you setting the absorb voltage lower, to say your float voltage, and then essentially gives you a two stage, bulk and float. I suspect some controllers will require absorb to be higher than float, in which case use 0.1 higher.

Your idea of using EQ to do absorb also occured to me. Havent tried it yet though. Since then midnite has announced that the next beta firmware will include a setting "days between bulk". Due any day now.

Cariboocoot

Re: Constant voltage charge

Sounds like he's talking about constant Float.

Doesn't work with PV because the sun does not shine all the time. Nor does PV start out with full power available the moment the sun starts to shine. Batteries get drained and need to be recharged when they do. If you only have 'X' hours to do it in because of the limited amount of sun available you have to charge them as quickly as possible to do this.

A car battery goes down in Voltage a small amount when it takes the hit from the starter. The alternator is able to supply a lot of current to boost it back up fairly quickly while maintaining a fixed system Voltage against the load demand.

Deep cycle batteries are going to go down quite a lot while keeping things running in the hours of no sun, and PV is not going to be able to suddenly push the system Voltage back up the way an alternator can.

Having worked extensively with both types of systems I can tell you they are not comparable in their function.

inthejungle

Re: Constant voltage charge

Thanks for everyone's thoughts


"Your idea of using EQ to do absorb also occured to me. Havent tried it yet though. Since then midnite has announced that the next beta firmware will include a setting "days between bulk". Due any day now. "

That sounds like a very interesting feature on the Midnight product, kind of stinks I don't have one!

Cariboocoot- this was my initial thought about hours of sun and trying to get as much as you can while you can. and that is why I wanted to double check and make sure I was thinking about things correctly.

I guess this leads me to the only question left, is the 7% discharge each day worth charging up or do I let it discharge more?

If I decide to let it discharge more, then what is the easiest way to accomplish this? Sometimes I am not around and I would like for it to do this on its own, but it may not be possible?
Do I just flip the PV breaker in the morning and skip the charge every other day?

Thoughts

NorthGuy

Re: Constant voltage charge

If you want to discharge the batteries more than you do, there are two ways to do that:

- Sell some of your batteries. The rest will discharge more.

- Use more loads. I'm sure you can think of ways to consume more energy.

stephendv

Re: Constant voltage charge

You could get close to what you're looking for by using the end-amps setting in the outback to end Absorb quickly if the battery is already charged. You won't be able to skip absorb completely, but you can make it last a very short time with end amps. I think that's about as good as you're going to get using the outback charger.