Keeps blowing 15 amp 12 volt fuse

[fredwrichardson]

We just came back from a two week vacation in the Ashland and besides the battery charger breaker having to be reset we had no issues. Even when running three ACs (in Orlando) the unit just ran fine. Now I am at home and I am running on 30 amps (put a 30 amp RV outlet on the side of the house) I am running just one AC to keep the RV from getting to hot inside. When I check the unit when I get home from work the bedroom and back AC panels are dead. The middle AC panel is fine and the is the one AC I am running. Also there is no power to the Fantastic Fan in the bathroom. I check the 12 volt fuse box and the red light is on for position 14. When I replace the fuse the two AC panels come back to life and the fantastic fan starts working again. It has now done this fuse blowing three days in a row. The panels says this fuse is "Back Wall / LP". Seems to be running to Domestic AC panels and the Fantastic Fan and none are running anything but are on. There is no wiring diagram to show me what actually is on that circuit so it is now a mystery. Does anyone have an idea what could be blowing that fuse. Strange that in only started happening when I am on 30 amps and not 50 amps. Also before we go after the 30 amp wiring the EMS system (and my multi-meter) says everything is fine and not sure how that would affect a 12 volt circuit. Any advise would be highly appreciated.

 

[danemayer]

Fred,

I'm not sure exactly how it's set up, but when the Power Control System sheds the load from the A/C units, I think it uses 12V DC to energize (or maybe de-engergize) a relay to interrupt 110V to the Air Conditioner's compressor. So there is some type of relationship between running on 30 amp service and the 12V DC system.

I'm not sure where the Power Control System gets the 12V DC to operate the relay, but if it's on the same fuse as the fantastic fan and thermostats, that would be the connection. You might pull the 110V Breaker Panel and see if you can find the 12V DC wiring related to the A/C breakers.

 

[fredwrichardson]

Fred,

I'm not sure exactly how it's set up, but when the Power Control System sheds the load from the A/C units, I think it uses 12V DC to energize (or maybe de-engergize) a relay to interrupt 110V to the Air Conditioner's compressor. So there is some type of relationship between running on 30 amp service and the 12V DC system.

I'm not sure where the Power Control System gets the 12V DC to operate the relay, but if it's on the same fuse as the fantastic fan and thermostats, that would be the connection. You might pull the 110V Breaker Panel and see if you can find the 12V DC wiring related to the A/C breakers.

Dan - I think you are on to something. Based on what I can see the Air Cond. panels do energize relays that control the 110V to the fan and the compressor of the AC. Still do not understand if the EMS cuts the 110V or the 12 DC when it sheds something but you gave me a place to start. Thanks - Fred

 

[fredwrichardson]

Dan - I think you are on to something. Based on what I can see the Air Cond. panels do energize relays that control the 110V to the fan and the compressor of the AC. Still do not understand if the EMS cuts the 110V or the 12 DC when it sheds something but you gave me a place to start. Thanks - Fred

Dan - you are right the Air Conditioners are controlled by the EMS through the panel by using 12 volt relays. The EMS actually sheds or controls the fan and the compressors using different 12 volt relays. That is why it will turn on the fans but wait two minutes to start up the compressor. It will also not let the ACs startup at the same time. Where I believe the issue is if you leave the Air Conditioner panels on (power to panel but AC is off) like I do the EMS will allow the second air conditioner to become unshedded (not sure if that is a real word) but because the panel does not have the air condition turned on we have a confused setup. I will turn off the AC panels completely tomorrow that are not being used and see if the fuse blows.

 

[danemayer]

Fred,

You also should run some tests to isolate what's on the fuse that blows. If with the fan fuse removedl (or blown), the A/C relay fuses have no power, that would establish the connection to the 30 amp scenario.

Something is blowing the fuse however. If you can link those relays to the fantastic fan circuit, I'd think about getting new relays. Also look for physical contact that might be causing a short. Maybe something needs to be taped.

Btw, I've been told that when the system sheds an A/C unit, the A/C fan still runs but the compressor is shut off. I'm curious if that's accurate because it implies that the A/C unit is wired to accept separate power for the fan and compressor, where the compressor power goes through the relay but the fan power doesn't.

 

[Birchwood]

Check the 30 amp receptacle on your house to confirm its not burned on the hot side.If its burned you could get cycling which can lead to all sorts of problems.

 

[fredwrichardson]

Fred,

You also should run some tests to isolate what's on the fuse that blows. If with the fan fuse removedl (or blown), the A/C relay fuses have no power, that would establish the connection to the 30 amp scenario.

Something is blowing the fuse however. If you can link those relays to the fantastic fan circuit, I'd think about getting new relays. Also look for physical contact that might be causing a short. Maybe something needs to be taped.

Btw, I've been told that when the system sheds an A/C unit, the A/C fan still runs but the compressor is shut off. I'm curious if that's accurate because it implies that the A/C unit is wired to accept separate power for the fan and compressor, where the compressor power goes through the relay but the fan power doesn't.

Dan - Today I am only going to have the one AC running and everything else off. If we can go through the day without blowing a fuse I will start adding devices and see what device is causing the overload. I am also going to get a detailed diagram on how the EMS sheds the AC units. This weekend I will meter the circuit and look at what type of load is generated as the EMS sheds and unsheds the ACs. Will let you know what I find.

 

[fredwrichardson]

Check the 30 amp receptacle on your house to confirm its not burned on the hot side.If its burned you could get cycling which can lead to all sorts of problems.

This was one of the first things I checked and everything looks fine. Also metered the outlet and again everything looks correct.

 

[danemayer]

Dan - Today I am only going to have the one AC running and everything else off. If we can go through the day without blowing a fuse I will start adding devices and see what device is causing the overload. I am also going to get a detailed diagram on how the EMS sheds the AC units. This weekend I will meter the circuit and look at what type of load is generated as the EMS sheds and unsheds the ACs. Will let you know what I find.

Fred, we have a couple of the Precision Circuits documents that may help. Here's a link. The Precision Circuits website also has an installation manual that may be helpful.

 

[fredwrichardson]

Fred, we have a couple of the Precision Circuits documents that may help. Here's a link. The Precision Circuits website also has an installation manual that may be helpful.

Dan - great minds think alike. I just downloaded all the documents. Looks like the EMS only controls the compressor and does not control the thermostat or fan. There does seem to be a shedding feedback to the thermostat so that it does not get an error when it tries to power the compressor and the EMS stops it from happening. There is a little hour glass that shows up when the A/C panels tells the compressor to run but the EMS stops if from running for two minutes. The interesting thing is that the EMS has this two minute delay even when it has NOT shedded the A/C. Seems the EMS always makes sure the A/Cs do not surge the system so the process is thermostat tells A/C to turn on so the fan comes on but the EMS stops the compressor from turning on for two minutes. At that time the relay from the EMS powers the compressor. If you have multiple A/Cs running it will also phase the A/Cs in making sure there is a two minute delay between powering each A/C. There is also another cool feature that we do not have on the Landmark. If you use their inverter and battery charger it will buffer the AC so you can startup two A/Cs on 30 amps by making sure you never exceed 30 amps by back filling power from the batteries through their inverter. A/Cs usually run more efficient as the compressors warm up so this is to get you through the time when the A/C first starts up. What I need to know now is how the relays are wired. As you stated earlier they could be setup that they need power to close the circuit or they need power to open the circuit. If they use power to open or shed the A/C this is where I might have a short causing the fuse to blow. Will try and look at that this afternoon.

 

[fredwrichardson]

Dan - great minds think alike. I just downloaded all the documents. Looks like the EMS only controls the compressor and does not control the thermostat or fan. There does seem to be a shedding feedback to the thermostat so that it does not get an error when it tries to power the compressor and the EMS stops it from happening. There is a little hour glass that shows up when the A/C panels tells the compressor to run but the EMS stops if from running for two minutes. The interesting thing is that the EMS has this two minute delay even when it has NOT shedded the A/C. Seems the EMS always makes sure the A/Cs do not surge the system so the process is thermostat tells A/C to turn on so the fan comes on but the EMS stops the compressor from turning on for two minutes. At that time the relay from the EMS powers the compressor. If you have multiple A/Cs running it will also phase the A/Cs in making sure there is a two minute delay between powering each A/C. There is also another cool feature that we do not have on the Landmark. If you use their inverter and battery charger it will buffer the AC so you can startup two A/Cs on 30 amps by making sure you never exceed 30 amps by back filling power from the batteries through their inverter. A/Cs usually run more efficient as the compressors warm up so this is to get you through the time when the A/C first starts up. What I need to know now is how the relays are wired. As you stated earlier they could be setup that they need power to close the circuit or they need power to open the circuit. If they use power to open or shed the A/C this is where I might have a short causing the fuse to blow. Will try and look at that this afternoon.

Have been running two A/C units on a 30 amp connect letting EMS manage the overload (shedding) when it happens. No more blowing fuses so not sure what happen but EMS is working great. After two full days I will have to say this has fixed itself.

 

[danemayer]

Maybe wiggling wires helped.

 

[fredwrichardson]

Maybe wiggling wires helped.

Spoke to soon. on the 5th day the fuse blew again. This is not going to be easy to fix.

 

[danemayer]

Fred,

Have you been able to determine whether the Power Control relays are on the same fuse as the Fantastic Fan and Thermostats?

 

[fredwrichardson]

Fred,

Have you been able to determine whether the Power Control relays are on the same fuse as the Fantastic Fan and Thermostats?

Dan - I am not sure and will try and isolate the relays this weekend. I do know that it is the AC activation that makes them blow for I was entering the RV when I heard the AC or ACs come online (I let some hot air into the RV) and the fuse blew at that time. The AC should of sequenced through the EMS system as one should of been shedded until current went back under 30 amps then the second AC should of come on (unshedded). I think it has something to do with both AC trying to come online at the same time and the EMS trying to shed one of the ACs.

 

[danemayer]

I think it has something to do with both AC trying to come online at the same time and the EMS trying to shed one of the ACs.

That's exactly what I'm thinking. When it tries to shed one of the AC loads, it fires that 12V relay and blows the fuse. That suggests to me that the relay, fantastic fan, and thermostats are all on the same fuse. If that's all true, I'd suspect the relay or the relay wiring.