[RE-wrenches] AC Coupled Magnum Issue

Ryan kb1uas at hotmail.com
Fri Mar 8 06:45:03 PST 2013


Drake

We use Magnums Router it has a Voltage based Aux relay. We then control a 2
pole SSR (Actually a 3 phase triac as that is a part we stock) to disconnect
the Grid Tie inverter. I tend to take the mindset that this is an Emergency
system so the concern of 3 stage charging when in actual AC coupled mode is
truly not important. If this was a normal off grid system doing AC coupling
than it would be a different story.

 

Ryan

 

Ryan Stankevitz

Technical Support Manager

MidNite Solar Inc.

ryan at midnitesolar.com

360-403-7207 XT 151 <tel:360-403-7207%20XT%20151> 

Skype ID ryan.midnite

 

 

 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Drake
Sent: Friday, March 08, 2013 9:40 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] AC Coupled Magnum Issue

 

Thank you to all who responded to this post. 

Larry, that sounds like a great potential solution. That will put the
frequency shift in line with where the battery cutoff voltage needs to be.
The frequency shift happens 2 volts above the absorption charge set point.
My only issue with the solution is the 1 1/2 hour round trip to the site (it
could be worse).  Maybe Concorde can give me information that will allow me
to set up the charge parameters without having to tweak.  

Allan, dump loads are a great way to go, for sure. The tech I spoke to at
Magnum recommended the relay as a fail safe for the frequency shift.  When
the issue of the inverter frequency shifting at 2 volts above the absorption
charge set point came up, the relay became the primary protective device for
the AGM batteries. 

We didn't use diversion loads since this is a backup system, and will
probably only operate a few days per year.  The inverter should maintain the
batteries rather than the solar. We used the Morningstar relay driver, in
part, to allow dump loads to be added if desired.  

Another solution was offered by APRS World, LLC.  They likely can build
products that would trigger relays using the temperature compensated data
from the Magnum Network.  

It would sure simplify life it Magnum could add an axillary relay.  Would
that require putting the inverter, or entire line of inverters, back into UL
for re-approval? 

Drake 

 
At 05:36 PM 3/7/2013, you wrote:



Meant to say, "You should tweak #3 & #4 above..."


Drake,

Charging an AGM battery does not have to occur at the maximum charge voltage
allowable; you can charge at a lower voltage for longer periods of time and
still achieve 100% SoC. Since you have grid power to work with, slow down
the charge cycle.

Assuming you have a late model ME-RC and version 5 or higher inverter, you
can custom program the charge voltages. Here's what I would do: 

1.	Go to Custom settings for battery type (setup menu 04). 
2.	Set the Absorb voltage for 26.8. 
3.	Set the Float for 26.4 
4.	Set the absorb time to 8 hours 
5.	Be sure the charge rate( setup menu 05) is 100%. 


Near the end of the absorb charge cycle, measure the current going into the
battery. If it is less than 0.2 amps/100AH capacity, the bank is full. You
should #3 & #4 above until it works out for the low temp. comp. and charge
time but it should work well.

If you are concerned about this lower voltage, set up a periodic equalize
charge to 28.8.

Larry Crutcher
Starlight Solar Power Systems





On Mar 7, 2013, at 3:00 PM, Drake wrote:

Hello Wrenches,

I had an unexpected glitch in AC coupling a Magnum 4024 PAE inverter.  The
system utilizes AGM batteries, which (according to Concorde tech support)
have a very strict upper voltage limit.

The relay used to stop the current input from the direct grid tie inverter,
when battery voltage is high, is controlled by a Morningstar Relay Driver.
The relay driver is set to shut off the charge at 28.8 volts.

The charger on the Magnum is set to charge the batteries to  28.6 volts.  

The plan was to be able to charge batteries from the Magnum without tripping
the AC connection between the grid tie inverter to the grid.  The Magnum
should charge to 28.6 volts, 0.2 volts below the relay driver's programmed
trigger point. 

There is one catch to using this approach. The Magnum inverter has a remote
temperature sensor in the battery bank. The relay driver is not temperature
corrected. Therefore, when the batteries are cold, the charging voltage goes
up in the Magnum.  This higher voltage trips the relay controlled by the
driver, and disconnects the grid tie inverter from the grid.  

I've played with the voltage set points, but the charge voltage on the
Magnum would be too low for good battery maintenance.  If these were liquid
electrolyte batteries, I'd crank up the voltage on the relay driver.  Since
they are AGM batteries, it doesn't seem like a good idea to do that. 

The work around for this at present is to; 

*	Charge batteries at night in the winter 
*	No problem is expected in the summer 

The batteries are in an insulated box in a shed connected to the house. The
inside of the battery box has a screened hole that is supposed to allow
heated air into the box.  This vent doesn't keep the batteries warm enough
to prevent the problem. 

Is there a temperature sensitive, voltage controlled relay or diver
available?  Has anyone used a temperature bulb with the relay driver in a
way that could solve this problem? Has anyone else come up against this
issue, and if so, what was your solution?

Thanks,

Drake 


Drake Chamberlin
Athens Electric LLC
OH License 44810
CO License 3773
NABCEP Certified Solar PV Installer
740-448-7328
http://athens-electric.com/ 
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