Shared Ground? (1 Viewer)

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I picked up a nice little deck on the weekend that had a USB port. I installed the thing only to smoke it somehow. It had a 10amp fuse on the deck itself and I also had another 10 amp fuse inline. The inline fuse got smoked but it didn't save the deck.

So before I go and try and buy another used deck and smoke it too, I thought I better figure out why this one got destroyed. The main difference from the stock deck to the new one is that the stock deck also uses the stock voltage converter for both memory and power. The new Sony deck I hooked up the memory wire to the stock converter and the ACC power wire to the aftermarket converter. The deck only has one ground wire, so I joined the grounds from both converters. There is a slight variation in voltage output between the two converters. The stock one puts out 13.94V and the aftermarket puts out 13.80V. Would the joining of the two grounds caused the deck to get fried?

BTW, I did re-install the factory deck and it works fine still.
 
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I picked up a nice little deck on the weekend that had a USB port. I installed the thing only to smoke it somehow. It had a 10amp fuse on the deck itself and I also had another 10 amp fuse inline. The inline fuse got smoked but it didn't save the deck.

So before I go and try and buy another used deck and smoke it too, I thought I better figure out why this one got destroyed. The main difference from the stock deck to the new one is that the stock deck also uses the stock voltage converter for both memory and power. The new Sony deck I hooked up the memory wire to the stock converter and the ACC power wire to the aftermarket converter. The deck only has one ground wire, so I joined the grounds from both converters. There is a slight variation in voltage output between the two converters. The stock one puts out 13.94V and the aftermarket puts out 13.80V. Would the joining of the two grounds caused the deck to get fried?

BTW, I did re-install the factory deck and it works fine still.

Ground is ground. They should both be at the same potential as they should both be connected to the frame and/or negative battery posts. Why wouldn't you just hook up the new deck using the stock wiring?
 
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The reason is that the frame ground is 24V. Both the stock and aftermarket voltage converters have a 24V negative (ground) input and a 12V negative output terminals. I presume they have 12V negative output terminals because it does make a difference with the frame ground on a 24V vehicle. I just don't understand what that difference is. Otherwise, there would only be a 12V positive terminal output on the converter and you would just grab ground from the frame or engine bock.
 

bj40green

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From the story you're telling I think the output of one (or both) of the converters is "floating" in other words; you have a 12 Volt output but the negative is not ground. It's 12Volt between the wires.
I think if you meassure between ground and the neg wire you'll read 12V and between ground and the positive 24Volt. So if you ground the negative you still have 24 Volts on the positive wire.
Those converters are build for boats with wood or polyester panels so no metal ground around. Does that make sense?
On the other hand you say that "BTW, I did re-install the factory deck and it works fine still." so that puzzels me.

Rudi
 
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I don't think that is it, other wise my 12V Cobra CB would have been screwed up. I have had that in the truck for over a year without a problem. The difference though is the CB mount is not grounded to the frame but the CD Deck is grounded to the frame on the mount. I'll have to check that with the digital meter. I only checked the current from the converters' ground wires.
 

bj40green

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As you said yourself: " The deck only has one ground wire, so I joined the grounds from both converters." and " Both the stock and aftermarket voltage converters have a 24V negative (ground) input and a 12V negative output terminals." means that there are different "ground" potentials. You just can't hook them up together. If all grounds were equal you won't blow a 10 Amp Fuse. 12V x 10 Amps = 240 Watts ! So you're dealing with different grounds. Not nice to figure this one out.
First thing to check out is if the 24V side ground is equal to the 12V side ground with an ohm meter. If the reading is 0 then its the same lead/ground. If the reading is OL (Open Loop) then you have a "floating" ground. Very tricky to deal with.

Rudi
 
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As you said yourself: " The deck only has one ground wire, so I joined the grounds from both converters." and " Both the stock and aftermarket voltage converters have a 24V negative (ground) input and a 12V negative output terminals." means that there are different "ground" potentials. You just can't hook them up together. If all grounds were equal you won't blow a 10 Amp Fuse. 12V x 10 Amps = 240 Watts ! So you're dealing with different grounds. Not nice to figure this one out.
First thing to check out is if the 24V side ground is equal to the 12V side ground with an ohm meter. If the reading is 0 then its the same lead/ground. If the reading is OL (Open Loop) then you have a "floating" ground. Very tricky to deal with.

Rudi

So if I had a floating ground, would that require the 12V side component to always be insulated from the vehicle ground? That would make it difficult to mount the deck without grounding it through the screws.
 
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I don't really know 24V systems, but 2 questions: are you sure the used deck was good? Why take any power off the second converter, just connect to one like your stock deck is?
 
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I don't really know 24V systems, but 2 questions: are you sure the used deck was good? Why take any power off the second converter, just connect to one like your stock deck is?

The seller had it hooked up to a batter and speakers in his garage. It worked fine when I bought it. That pretty much points to me F'in it up. :eek:

The stock converter maxes out at 3-5 amps - not enough juice for a CD deck but fine for a stock cassette deck/radio. However, the stock converter will not drain down the batteries, so I use it for the memory power wire.

<I left the truck for 6 week at SEATAC once and it fired up no problems. I had actually planned to disconnect the batteries but arrived late and forgot.>

The aftermarket converter, if always on, will drain down the batteries.

I am thinking that my best solution will be a big third battery. I am going to need it to power the CPAP machine anyways or my camping days are over.
 

bj40green

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So if I had a floating ground, would that require the 12V side component to always be insulated from the vehicle ground? That would make it difficult to mount the deck without grounding it through the screws.

It's difficult to imagine what the exact situation is from your descriptions. I can only say that if you connect (assumed) grounds together and you blow a 10Amp fuse, in fact you are grounding a live 12V (or 24V) power line.

Rudi
 

seatosummit

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When I tackled this issue I didn't bother with memory and presets and just directly connected the live output from the converter to the positive input on the back of my deck. The negative input on the deck was simply grounded out to the body without issue.

I noticed that the voltage from the positive lead on the converter to the negative lead on the converter and to the the frame was the same (cerca 13.7). This is a good place to start. If the ground is indeed floating then a solution is beyond me...but then again that really isn't saying all too much.
 

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