Electrical System Brainteaser

[Roach_Coach]

I spent the day troubleshooting my 1993 Four Winds Class C Coach electrical system.

Kind of as a fluke, I checked the voltage on one of my overhead RV lights and noticed it was about 16+ volts. I wanted to know why, so I checked the power converter. I have a MagneTek 6345 power converter, and it functions as it is supposed to. However, what I did find is that I have a car stereo that was installed by the previous owner into the coach DC system (just off one of the lights.) When the converter is not powered (i.e. on batteries only) the stereo operates normally and the voltage on that circuit is normal (12.4ish.) However, when on converter power, the stereo still operates, but the line voltage on that circuit is very high (17ish.) When I unplugged the stereo, the voltage drops back to normal.

Anybody have any ideas why? I am an amateur electrician at best, just enough to be dangerous with a multimeter 😉

Thanks,
Lou

p.s. I know I should buy a new power converter because these are notoriously bad. However, I'm not sure that is the problem in this case. I tested the charger output (13.2v) and the converter output (12.4v)and they are normal.

[Dakzuki]

A) Clean all your battery connections. They should be bright and shiny when you connect them. Your converter may be seeing a big voltage drop with the stereo running (high resistance at bad connections) and dumping lots back into the system.

B) By a Progressive Dynamics converter....just because you should.

[time2roll]

17 volts? Fine what fuse protects that branch and recheck voltage at the fuse.
BTW if the battery in the voltmeter is getting weak it is common to read high. Change that first.

[Harvey51]

It seems to me that in order to raise the voltage a device would have to be a power source sending current out into the batteries. The fan or the stereo could then be used to power the whole RV - no converter or batteries needed. Voltage is the "energy per unit charge". The fan is adding energy to the charges passing through it when it increases the voltage,

[Roach_Coach]

Harvey51 wrote:
Just a thought - the stereo may draw a lot of amps from the DC system, pulling the battery voltage quite low thus convincing the smart converter that it needs to go into its highest charge rate, which would be at about 16 Volts. If the stereo requires more than 300 watts (25 amps), I would consider a separate 12 V power supply for it when connected to shore power. Does it shake the whole RV and rattle the neighbours' dishes? If so, consider a lower power stereo with headphones for the listeners. Sorry I'm a little negative on loud music; it is the result of living across the street from a high school student parking lot where some student cars have the entire back seat area filled with massive stereo systems that rattle our dishes.

I don't think the stereo draws that many amps since the problem occurs even with the stereo turned off--it just has to be plugged in. I agree with you about the loud music (my system doesn't have any sub-woofers or anything) no rattling dishes here!


Fisherman- I like the diode idea, I think I'll try it

Scott- Replacing the power converter is definitely on my short list. Unfortunately, my short list is pretty long!:S

[ScottG]

I know it's a spendy fix but your best bet is to dump that MagneTek and upgrade to a 3 stage converter. Your battery will thank you.
Plus, it will die someday when you least expect it, leaving you with a dead battery.

[You_can_t_take_]

When 'Shurflo' first came out with a roof vent exhaust fan I purchased one and installed it in one of my roof vents. Then I started burning out light bulbs, the little bathroom exhaust fan, even the batteries were getting overheated, etc. I checked the voltage on my light fixtures since they seemed to get brighter every time the 'Shurflo' fan came on. Sure enough I was getting readings of more than 20 volts! The fan was feeding higher voltage back into the 12V system when it was operating! I contacted 'Shurflo' and they admitted that their ceiling vent fans were causing some problems in some trailers. They had redesigned their circuit boards as a result of these problems and added a diode to boards where the power supply was connected. They sent me a diode to connect between the incoming power wire and the connection to the fan and all my problems immediately disappeared.
I would suggest that you go to an electronics store and pick up and install a diode to the wire that connects your radio. I think that will solve your problem.

[Harvey51]

Just a thought - the stereo may draw a lot of amps from the DC system, pulling the battery voltage quite low thus convincing the smart converter that it needs to go into its highest charge rate, which would be at about 16 Volts. If the stereo requires more than 300 watts (25 amps), I would consider a separate 12 V power supply for it when connected to shore power. Does it shake the whole RV and rattle the neighbours' dishes? If so, consider a lower power stereo with headphones for the listeners. Sorry I'm a little negative on loud music; it is the result of living across the street from a high school student parking lot where some student cars have the entire back seat area filled with massive stereo systems that rattle our dishes.