Trouble Shooting 12v power supply for fridge

[pablosgirl]

Hi All,
Need some trouble shooting help with a 12v power supply for the fridge.  I have just finished installing a 12v power supply using John Nixon's wiki artical to run the fridge off shore power when at the dock to save the batteries and charger from extra work.  Seemed simple enough.  But I can't seem to get a +12v reading from the power supply when it is entergized.  I measure 120.8vac across the N & L leads but when I measure from the common and either the +12 or -12 terminals I get a voltage in the millivolt range.  If I connect the 12+ terminal to the "85" terminal of the relay, I get -12.9 v on the 2 -12v terminals but the same low millivolt readings on the +12v terminal. If i connect the "87" relay terminal to the same +12v terminal on the power supply I still get -12.9v on the -12v terminals and lov millivolt readings on the +12v terminals.  If I dissconnect the "85" terminal of the relay, then I get low millivolt readings on both the -12v and +12v terminals.

The power supply is a Mean Well HRP-300-12 (300Watt, 12v power supply).  The boat is an 88"  MKI (hull #551) so I have the older, more power hungry unit.  The question I have is, am I dealing with a bad power supply or a bad relay?  I have rechecked the relay connections versus John Nixon's drawing on the wiki several times and I am pretty sure that those are correct.  The fridge runs on the battery source through the relay so at least the relay is functioning in its non energized state.  So I am leaning toward a bad power supply.  Do any of you out there with a 12v power supply able to read 12v across the terminals if the power supply is not connected to a load?  Any insite into further testing steps would be appreciated.

Paul

[2ndwish]

Looks to me like the power supply you are using has floating outputs. 12 V should be measured between the V+ and V- outputs not relative to common.

[pablosgirl]

Hi 2ndwish,

Yes I checked after your sugestion and measured 12.9v across the -12v and +12v terminals.  Dose this mean that I will connect my negative lead of the fridge to the -12V terminal instead of the common?
Thanks,
Paul

[2ndwish]

Yes. This will actually connect the -V output to your boat's ground/common. You might have to experiment with where that connection is made for electrical noise immunity (your supply operates at a switching frequency of 70 KHz), although since you are only running the supply at dockside it should not be too much of  concern. If you hear noise on your VHF or stereo when the supply is on, you probably need to move that connection. There are really 4 possible places to make the connection: at the power supply, at the fridge, at your vessels bus bar or at the engine.

As a safety note: Since the supply can source >20 amps you should probably place a fuse in the V+ line. 

[Ron Volk]

Paul,

Have you connected contact 87 to contact 85 with a strap, I found these contacts not to be connected internally in the the relay and you need to do it manually.  I have the MW HRP-300 and the Tyco 4-45f11 relay and could not get power to the compressor until I added the strap and then it has worked perfectly.

[pablosgirl]

Hi Ron,

Thanks for the tip.  I saw your note about this in an earlier post about the fridge power supply and I have the strap in place.

Paul

[Ron Volk]

Paul,

Thanks for the reply.  When I continued to have problems with the old power supply I called MeanWell, they are in the SF Bay Area.  I talked to one of their techs and he went over all the specs and readings with me, maybe they can shed some light on the problem.

[pablosgirl]

Hi Ron,

I was able to get to the boat last night after work and moved the negative lead to the -V terminal and it works as expected.  I turned the power supply output voltage up to 13.2v thinking that this would reduce the curent draw a little and be better for the motor/compressor.  Please correct me if this is a mistaken assumption.

Paul

[Ron Volk]

Paul,

Good to see you figured it out and it works.  I don't leave mine on all the time as we live about 2 hours from the boat and we get over about every two weeks and usually stay for 3-5 days at a time, but when we are there and in port we keep it on all the time and it works fine. I used Johns information to install mine and I believe he said that the Alder/Barbour compressor works most efficiently at 13.2V so thats where I set mine also.
We have very good friends in Houston we visited and one day we drove down and toured the Space Center and then contined on to the Kemah boardwalk for dinner which is probably close to where you keep your boat.

[pablosgirl]

Hi Ron, yes those places are close.  We live 1/2 mile from NASA and keep the boat on the south side of clear Lake.  We motor by the Kemah Boardwalk to get to Galveston Bay to sail.
Paul