FIXED: 12 V Power Supply low

[jimtoo]

Got my refrigerator back this morning and after installation it would not come on. New circuit boards were installed, still would not come on and start cooling. Voltage was checked at fridge connection point and was only getting 11.5volts. Pulled 12v fuse panel, voltage on fuse panel outlet side of fuse was 11.5v, while on inlet side of fuse it was reading 13.5v. This is one of the fuse panels that has the led's that come on if fuse is bad. We bypassed the fuse for the fridge, fridge came on, installed original circuit boards and it still worked OK. Tech said it takes a full 12v for fridge to come on and start cooling. Checked it this evening, everything still OK and fridge is cooling. The fridge does have it's own fuse, 5amp, on circuit board, so it's still protected.

All the connections were checked on the fuse panel, they are all tight and no corrosion. All outgoing connections on the fuse panel have the 11.5v reading, not just the fridge. Has anyone had a problem with the fuse panel it self causing a drop in voltage? (I don't remember seeing any post about it.) In my way of thinking there must be something wrong with the circuits that feed the LED's causing the 2volt drop across the fuse. Will be doing more checking tomorrow to see if possible to bypass or do away with the LED indicators for the fuse panel.

Jim M

 

[57chevyconvt]

Re: 12 v Power Supply low.

Jim,
I know that your refer is different than mine (RM1350IM) but the 5 amp fuse on the control board is for the 120 V side of the feed to the board and the 3 amp fuse is to the 12 V side of the board. I have an inline 4 amp GM type of fuse in the 12 V feed to the teminal block which in turn feeds the 12 V side of the Control Board. I have no idea the source of voltage drop across the 12 V fuse panel. I believe the LP Gas detector is also on the same fused circuit as the refer.

 

[jimtoo]

Re: 12 v Power Supply low.

OK Jim Thanks,,, I have been out in the trailer myself just now since I made the original post. I just could not believe what was happening. I have been in the auto, truck repair most of my life and know 12v circuits pretty good. But I was taking someone else's word for what was happening, even thou I had my meter checking also at a couple of different places, I was getting the same readings,, just not going deep enough in my checking. After all he is a certified tech. Here is what I found.

If a fuse is burned or blown, the 12volt fuse panel with the LED indicators will still let you get a 11.5v reading at the load connection,,, but will not let any amperage be pulled through the circuit. The load (bulb or fridge in my case) is acting as a ground for the LED and this is what turns the LED on. The LED's are evidently wired across the fuse connectors underneath so that when the fuse goes the LED will turn on. So a blown or burned fuse will read 13.5v on the supply side and 11.5v on the load side. I know or will bet that when they installed the fridge and was hooking up the 12v supply (it was on, they did not disconnect battery) that the helper shorted or blew the fuse. So when the fridge did not come on, it still had a 11.5v reading at the fridge connector. When the repair tech pulled all the fuses and checked voltage everywhere, it was reading like I think it was supposed to. I think the repair tech has never had service problems with this type of fuse panel and did not know what was happening. When I went out tonight and turned on the entry light it did not come on, that is when I started measuring voltage and found that a good fuse measures the same on both sides, but a blown or burned fuse will read 13.5 input and 11.5 on the output or load side. So in the morning I will reinstall the wiring to fridge in the correct place with a fuse in the panel and recheck everything again. Hope this is not to confusing.

Will let you know more tomorrow.

Jim M

 

[danemayer]

Re: 12 v Power Supply low.

If a fuse is burned or blown, the 12volt fuse panel with the LED indicators will still let you get a 11.5v reading at the load connection,,, but will not let any amperage be pulled through the circuit. The load (bulb or fridge in my case) is acting as a ground for the LED and this is what turns the LED on.

Jim, if you're saying that the fuse is blown, was the LED lit up?

 

[jimtoo]

Re: 12 v Power Supply low.

OK,, this morning I checked the fridge, it is cooling good, temps about 6-8 in freezer and 35-36 in fridge. So it looks like it is working correctly.

I do not know if the LED indicator was on before tech started pulling fuses and measuring voltage. I will do some more checking after we return from Kerrville Sweetheart Rally.

I did hook my fridge back up on the fuse panel with a fuse in place and it is working correctly.

Jim M

 

[porthole]

Re: 12 v Power Supply low.

Good catch. Now we wait to see if your LED is bad and not alerting you to the bad fuse. Sometimes things that are supposed to make life easier make things more difficult.

The drop between 13.5 to 11.5 has me curious. Diodes have a .6 of a volt drop across the pins. Is the 2 volt drop just because there is a potential load on the other side?
Haven't checked yet but if there is no circuit drawing any current will the LED still light up (on a known good circuit)?

 

[wdk450]

Re: 12 v Power Supply low.

OK Jim Thanks,,, I have been out in the trailer myself just now since I made the original post. I just could not believe what was happening. I have been in the auto, truck repair most of my life and know 12v circuits pretty good. But I was taking someone else's word for what was happening, even thou I had my meter checking also at a couple of different places, I was getting the same readings,, just not going deep enough in my checking. After all he is a certified tech. Here is what I found.

If a fuse is burned or blown, the 12volt fuse panel with the LED indicators will still let you get a 11.5v reading at the load connection,,, but will not let any amperage be pulled through the circuit. The load (bulb or fridge in my case) is acting as a ground for the LED and this is what turns the LED on. The LED's are evidently wired across the fuse connectors underneath so that when the fuse goes the LED will turn on. So a blown or burned fuse will read 13.5v on the supply side and 11.5v on the load side. I know or will bet that when they installed the fridge and was hooking up the 12v supply (it was on, they did not disconnect battery) that the helper shorted or blew the fuse. So when the fridge did not come on, it still had a 11.5v reading at the fridge connector. When the repair tech pulled all the fuses and checked voltage everywhere, it was reading like I think it was supposed to. I think the repair tech has never had service problems with this type of fuse panel and did not know what was happening. When I went out tonight and turned on the entry light it did not come on, that is when I started measuring voltage and found that a good fuse measures the same on both sides, but a blown or burned fuse will read 13.5 input and 11.5 on the output or load side. So in the morning I will reinstall the wiring to fridge in the correct place with a fuse in the panel and recheck everything again. Hope this is not to confusing.

Will let you know more tomorrow.

Jim M

Jim:
GREAT analysis and explanation of something all of us tech types with DVM's checking electrical problems will see. I guess we pay for the convnience of LED blown fuse indicators with misleading voltage readings on the load side of the fuses. Maybe they should have tied the plus side of these LED's together and run them through a momentary "TEST" switch to eliminate these false troublleshooting voltage readings.

 

[Boca_Shuffles]

Re: 12 v Power Supply low.

Good information for us all.

If you have a circuit that isn't working properly, you should do a continuity check on the pulled fuse. You already have your meter out.

Those fine wires and plastic coated fuses are hard to see.