[RE-wrenches] Programmable Battery Charger

Tue Dec 16 12:35:10 PST 2014

Hi:

I'm enjoying learning many new ways of looking at things and of practical 
solutions on this forum.  In that spirit, the only thing I would add to 
this discussion is that the power factor as seen by the AC source will be 
very poor.  In that regard, the larger the caps, the more stable the "DC" 
voltage, but the poorer the PF.

This will show up as much lower charging efficiency due to the way in 
which AC current is drawn by the bridge rectifier/capacitor circuit. 
Here's an actual graph of how a bridge rectifier connected to a capacitor 
draws AC current,

The graph is from my past life a couple of decades ago back when I was 
studying.  It's not a conventional phase-shift PF problem, but rather a 
form factor PF problem.  It shows the current drawn by a 13" PC monitor of 
that era, before PF correction was mandated for all new products.  In this 
example the 'crest factor', (peak current as measured versus what it could 
have been if the current was drawn throughout the AC pulses, was about 
4x).  Depending on the size of capacitor, it can be as high as 7x.

The practical effect on the wires and devices including the diodes and 
charge controller, is that a lot of heat is generated in their power 
components.  The source of the energy for that heat is the AC source and 
in cases where the AC source is a generator that translates to much higher 
fuel consumption, (in some cases over 30% more).

Out of my tests back then, I also discovered one practical recommendation. 

If you are using bridge rectifiers connected to capacitors, do not have 
any length of wire and in particular no loop area in the wires between the 
bridge rectifier and capacitors.  Having wire/loop area introduces 
inductance into the circuit which behaves somewhat like an ignition coil 
due to the high speed reverse recovery period of the diodes; and this 
happens four times every AC cycle.  Given the right conditions the voltage 
spikes caused by that inductance/ignition coil like effect will make short 
work of the diodes and other components which are on the circuit.

The voltage spikes wont be a problem if the bridge rectifier is as close 
as possible to the capacitors, but due to reverse recovery effect, you'll 
still be stressing the parts and heating wires.

In my opinion, its ok to do this, but I wouldn't push power levels to 
anywhere near the limits of components and devices.

JARMO

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Jarmo Venalainen  |   Schneider Electric   |  Solar Business  |   CANADA | 
  Training & Development Specialist - Senior 
Phone: +604-422-2528  |   Fax: +604-420-1591  |   Mobile: +604-505-0291 
Email: jarmo.venalainen at schneider-electric.com  |   Site: www.SEsolar.com 
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*** Please consider the environment before printing this e-mail 

From:
"boB at midnitesolar.com" <boB at midnitesolar.com>
To:
RE-wrenches <re-wrenches at lists.re-wrenches.org>, 
Date:
12/16/2014 11:16 AM
Subject:
Re: [RE-wrenches] Programmable Battery Charger
Sent by:
"RE-wrenches" <re-wrenches-bounces at lists.re-wrenches.org>

Larry, Pitfalls ?
The biggest pitfall I would say is if you have a VERY stiff grid.

If your Voc is say, 170V DC and the CC current limits it output at say, 
169 V DC,
they you are going to need to add an input power resistor of a couple Ohms 
to
help cushion the input to be more like a PV module.  A lot of times, the 
grid is
not nearly this bad, especially generators.

Also, If you are going to do this, I would NOT use Solar mode but instead 
try
Hydro mode set to Manual MPP voltage.  First start the MPPV at something 
just
less than Voc or maybe, say, 160 VDC.  Then, from main STATUS screen, you 
can
adjust the input voltage up and down by pressing the Soft-Right or 
Soft-Left
keys respectfully.  (upper right and upper left keys).  Then you can 
manually get
a feel for what it should be set for.

The Classic 200 is the only CC of ours that I would use.  The 250 would 
work but the
200 is much more suited.  I wish there were a real charger that one could 
buy that was
isolated, and we have never really advocated MPPT charge controllers for 
this but
in a pinch, they always seem to work find.  Never did add a "DT" mode 
(after Daryl
Thayer of course), but this hydro mode seems to work OK.

If you want to let it sweep but setting it to 3 minutes (or higher) that 
will also work.
If you do that, set the minimum input voltage.  Something like 140V or so 
will keep
it from dropping the input voltage too low and either bogging down the 
input source
and the rectifier bridge (especially generators)

You can also set the INPUT current limit in the LIMITS menu.  This was for 
hydro
in particular.  Either limit can help reduce Isc or bogging down issues.

The other pitfall is that it is NOT galvanically isolated so you should be 
very careful.
We use an X240 equivalent transformer to keep the batteries going in our 
burn in
rack using 2 Classic 200s and it works great.

Also, use a nice and strong full bridge rectifier so that it applies 120 
Hz instead of
60 Hz to the input.  That is much easier on the input capacitors and 
things and just
makes it work smoother.  There are input capacitors (filtering) on most 
charge controllers.

Again, in a pinch this seems to work but watch that input max power point 
voltage to make
sure it is not too high compared to the Voc.  If there isn't enough 
voltage spacing between
the two (stiff AC source) then the control isn't going to be very smooth 
and might risk
letting the smoke out.

What ever you do here, be very careful what you touch !

boB

On 12/16/2014 6:39 AM, Larry wrote:
I must have missed the prior discussion about using PV CC. The concept 
sounds good but how many of you have done this and are there any pitfalls 
to be aware of? If I use a 20 amp bridge I should be able to produce 80 
amps @ 14.4V. For continuous operation, will I need a large heat sink on 
it?

How does the unfiltered full wave peak voltage affect the CC over time? 
Are they (specifically Midnite) really designed to handle input waveform 
like this? I like this idea, especially if I can stack the controllers.
Thank you,

Larry 
On 12/15/14 6:51 PM, jay peltz wrote:
Hi Kirk, 

If you use a 200vdc midnight CC you'll have no issues.
When you rectify 120vac its up around 166vdc
( uses the peak vac which is around 170vac.)

For a 150vdc max controller ( midnite 150)  or a 144vdc ( outback FM) then 
a buck transformer or standard transformer is the trick to reduce the AC 
and hence the DC for these lower voltage units.

jay
peltz power
On Dec 15, 2014, at 5:38 PM, Kirk Herander wrote:

This has been discussed on this list in years past. It is possible to use 
an outback charge controller as a battery charger. You need to put the 120 
AC into a bridge rectifier, then feed the 120 DC into the controller’s PV 
input. So you’ll have an 80 amp battery charger.

Kirk Herander
VT Solar, LLC
Proven PV provider since 1991
www.vermontsolarnow.com
dba Vermont Solar Engineering
NABCEPTM Inaugural Certificant
VT RE Incentive Program Partner
802.863.1202

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On 
Behalf Of Dan Tittmann
Sent: Monday, December 15, 2014 8:18 PM
To: info at windsine.org; RE-wrenches
Subject: Re: [RE-wrenches] Programmable Battery Charger

You can manually adjust Iotas with tweaking the potentiomiters while 
monitoring it with a god volt meter. But no time adjustment.
Daniel

Daniel Tittmann 
CTO
Greenwired
www.greenwired.com
daniel at greenwired.com
707-923-2001 (office)
707-206-5088 (Cell)

On Mon, Dec 15, 2014 at 4:21 PM, Windsine Inc. <windsine at gmail.com> wrote:
Check out Argus Technologies.
RoyR
On Dec 15, 2014 4:01 PM, "Larry" <larry at starlightsolar.com> wrote:
Wrenches,

Does anyone know of a 120/12 volt battery charger that can be programmed 
for absorb and float voltage and time in absorb mode? I have been needing 
this product for many years but I can only find it in inverters with built 
in chargers from Magnum, Outback, and Xantrex.

-- 
Thank you,

Larry Crutcher
Starlight Solar Power Systems

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