[RE-wrenches] PV excellent battery charger

[bob]

Hi gang
This is a little off topic but covers battery charging in general.
In an industrial charger situation you don't have the time to wait for the
sun to charge the battery bank. You work the hell out of them for 8 or 16
hours, charge them overnight, then you do it again! The vast majority are
just big "taper" type chargers, with minimal controls.
As solar installers we would love to have all our customers buy enough solar
to charge daily in the available amount of sunlight, wouldn't we?
I have seen forklift batteries taken to the service shop from an industrial
freezer and they had to wait for 3 days for the battery to thaw out before
they could service them.
The industrial chargers that I deal with are primarily 3 phase 480 or 640
volts. The last time that I replaced one, I asked about temp compensation on
the new unit and was amazed when I was told no one did that. It's just a big
dumb battery after all...
There are some chargers out there that I can best describe as a "high
frequency" charger. They are small wall mounted units that have a sound that
you will not mistake for anything else once you've heard it. They seem to
charge in bursts of varying length and help keep the battery temp down that
way.
The battery shops I know hate them, the only way to service them is to bring
a truck full of circuit boards and replace them till it charges correctly!

We mostly use Magnum inverters now as they have a better charger than
Outback and most of the jobs are off grid. Both are good units as we are all
well aware, but the Magnum charger does more charging with less AC power
input. The 4024 does something 105 amps v/s 70 amps DC as a charger and I
think the AC draw is still less. Magnum's weak spot, still no reverse power
input protection to save some dummy who happens to reverse the in and out
hot leads! I hate days like that.

The short answer would have been that we treat our batteries better, charge
quality wise on a bad day, than most industrial sets get treated on a good
day!
Needless to say that would not include owner abuse or neglect, we all see
that.

Later,
Bob


 

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of R Ray
Walters
Sent: Thursday, March 25, 2010 5:59 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] PV excellent battery charger



On Mar 25, 2010, at 5:55 AM, Warren Lauzon wrote:

> Actually, PV is not a particularly excellent battery charger,

What is better than a properly sized array with the latest controllers?

> 
> Everything else mentioned can be done by any decent AC battery charger.

True, but at great expense. The traditional AC chargers like the ones made
by Lester are industry standards, and are archaic in comparison.
Now chargers that come with say an Outback Inverter, that was installed as
part of a solar system, do have everything as you mentioned except I'm not
sure about the PWM.
We'd need to hear from Chris Frietas or some other Manu rep to further
explain the charge regulation on the Outback inverters, and whether it uses
PWM.
Outside of the solar industry, batteries are not treated near as well.

Ray

> 
> 
>> My understanding is that the voltage, in excess of battery voltage, from
>> the array, represents energy that is dissipated as heat in the batteries.
>> This extra voltage, multiplied by the amperage is wattage. This extra
>> power can produce more amps at a reduced voltage.  It is amperage that
>> charges the battery.
>> 
>> Thanks,
>> 
>> Drake
>> 
>>> MPPT doesn't really do that much for the battery, it just makes the PV
>>> modules more effective.
>>> The real magic is:
>>> A) the 3 stage charging (compared to traditional single stage AC
chargers)
>>> B) Temperature compensation
>>> C) PWM that helps pulse off sulfation
>>> D) Slower charge rates let batteries charge more fully without damage
from
>>> overheating.
>>> 
>>> R. Walters
>>> ray at solarray.com
>>> Solar Engineer
>>> 
>>> 
>>> 
>>> 
>>> On Mar 24, 2010, at 7:04 PM, drake.chamberlin at redwoodalliance.org wrote:
>>> 
>>>> Can anyone tell me why PV is considered an excellent battery charger? I
>>>> think it is, only after the addition of a MPPT charge control.
>>>> Otherwise,
>>>> the battery drags the PV voltage below Vmp.
>>>> 
>>>> One of the NABCEP objectives for the entry level class is to explain
why
>>>> PV modules make excellent battery chargers and show this through the IV
>>>> curve.
>>>> 
>>>> Thank you,
>>>> 
>>>> Drake
>>>> 
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