A T@B 12 volt circuit challenge, power while fuse removed from the circuit

jimcenname

While on battery (2X6-volt AGMs and no solar and no shore power) power I measured voltage at the maxxair cabin fan leads at 12.6 volts. I removed the 7.5 amp fuse in the under-seat fuse panel to do some work on the fan and also removed the fan from the circuit. With the both out of the circuit I measured the voltage across the power leads at 6 volts both to neutral and ground from the hot wire. Why would I have a normal 12.7 volts with the fuse in and 6 volts with the fuse removed. 

Denny16

That is odd...

Cheers

m_lewis

If your fuse box is the same as mine, there is an LED that lights when the fuse is blown.  This feature allows some voltage to pass on to the load when the fuse is removed. I haven’t measure it, but 6 volts is reasonable. BTW, if the fan (and all other loads on the fuse) is off, there would not be a path to ground for the LED to light.  

peterjoce400

you don't mention why you were pulling the fuse.  Our problem with the Maxx was the beeping and green light.  At the time we were on shore power and we lost all control of the unit; we found that pulling fuses didn't turn off the unit.  Only switching off the master and pulling the shore power could we get a reset.  Maxxair advises me to measure voltage on the unit ( have to open it by the control buttons) as it seems these things are very voltage sensitive.  I have to wait till spring to get at that but in the meantime am interested in hearing of others having issue with their Maxx.  ( 2019 T@B 400)

jimcenname

@m_lewis, I think you solved the mystery. My fuse box does light near the fuse and I noticed when I opened the circuit by removing the fan the light went out. I'll test again to see when I apply the volt meter if the fuse lights but I bet that's it! Thanks

jimcenname

@peterjoce400, I pulled the fuse to reset the maxxair, that method works for me. Long story-short I have the same problem you do but it is intermittent. To solve the problem Maxxair sent me a new circuit board that is supposed to fix the voltage sensitivity problem but in the 2-weeks it took the board to arrive the problem went away. Now several months later it's resumed so I put the new board in the Maxxair today which is when I was measuring the 6 and the 12 volts and scratching my head. I think @m_lewis solved that mystery. FYI, When NuCamp installed the Maxxair, after-factory, within two days the fan started misbehaving. Per Maxxair diagnostic suggestion I found the voltage supply to my fan to be 13.67 volts back then. It read 13.67 volts two days ago on shore power but I was off shore power today and the problem occured at 12.7 volts. I hope the new board fixes it. I recall someone else with the same problem was offered a new motor from Maxxair. 

peterjoce400

Will be interested to hear update on the new board installation and if that corrects. 

jimcenname

2 weeks later, after circuit board replacement and fan is working well. No beep and green light. 

Michigan_Mike

How difficult is the board change out project?  Is it a unplug and plug it in deal?   And the voltage reading sounds reasonable, 13.67 volts when plugged into shore power would be the electric converter charging up the battery and you should get that read and the12.7 volts when off shore power and a fully charged battery.   I have the multi speed Cadillac version of the Fantastic-Vent and will say that it does have its nuances.  I was taken aback with my 400 one day in the barn as I noticed my step light was on after I had turned off the battery switch.  But the trailer was plugged into shore power so that solved that issue once I unplugged the unit.  😂

ChanW

Well, I'm glad you fixed it, but I'm curious what is 'neutral' in the supply to the Maxxair? There oughtn't to be "neutral and ground" in your DC Maxxair circuit! (Not sure if oughtn't is a word  )

jimcenname

@Michigan_Mike To replace the board I had to remove the screen, black manual handle and the plastic shroud. The shroud has a few screws securing it. The board is fastened to the back of the shroud by a few screws. I cut the black and white wires providing power. One is hot and the other, I assume, is neutral. I am not an electrician so I don't know if neutral and ground are the same thing on a vehicle. Once the wires are cut I moved the shroud/board assembly to a table and swapped the board. There is a sensor that is hot-glued into place that is hard wired to the board. I had to break that free too. Upon reinstalling I am not good at crimping wire lugs so I use wire nuts and tape to reconnect to power. I work slow, it took me about a hour. 

ChanW

I wasn't sure if you had a third wire you were calling neutral, when you said 'neutral and ground'. 

Neutral is usually referring to AC wiring, vs DC which has two conductors, positive or "hot", and negative (which is sometimes ground). In an AC circuit you'll have three wires which are hot, neutral, and ground - ground and neutral not being the same.

jimcenname

Update Feb 2021, "beeping again". After experiencing the supposed voltage fluctuation error and as mentioned earlier in this string I replaced the control circuit board in my Maxxair 7500. That worked for awhile. A month or so later I increased the fan speed to 50%, which I hadn't done before and the fan experienced the error. The beeping and then the fan powered down. After restart, every time I increased the fan speed to 50% the green light beeped and the fan shut down. I will note that unlike before I didn't have to remove power from the fan circuit to reset. Once the beeping stopped I could restart the fan. Anyway, I called Maxxair and after some back-and-forth, they sent me a new fan motor. I just replaced that, which wasn't too difficult, and I can now operate the fan at 100% with no error. Let's see what happens.