Voltage drop

[rickf1985]

I have a voltage drop of about 2 volts between the engine/battery and the instrument panel. I can not find any bad connections or corroded wires. I realize I am going to have to do some rewiring but I would like to improve on the original setup. I would like to run a DC duplex wire up to the front and put in a DC minus bus bar and a DC positive bus bar. The ground would be direct to the batteries and the positive would be switched through a relay triggered by the original ignition wire. I figure I could eliminate three or four seperate grounds back to the battery this way and also get full power to the gages. What are your thoughts and suggestions?<br />Rick

 

[Dunaruna]

Re: Voltage drop

Hi Rick, welcome to i-boats!!<br /><br />What motor setup do you have and do you have a good DVM?<br /><br />Aldo

 

[jlinder]

Re: Voltage drop

I would suggest you take a good DVM and take a couple of readings.<br /><br />Put one end of the meter on the ground wire at the instrument panel and the other at the battery minus post. Record this number.<br /><br />Do the same between the positive wire at the console (fuse block?) and the positive post of the battery. Record this number.<br /><br />You now know the voltage drop on both the power feed and the return. If the ground and power wires are the same size, the voltages should be the same. If not, the wire with the higher voltage drop has a problem.<br /><br />Also, try to measure or estimate the length of these wires, and read the guage of the wire.<br /><br />Post your results, this will help you trouble shoot your problem, and maybe find a solution.

 

[Barnacle_Bill]

Re: Voltage drop

Crimped on connectors can get corroded inside where you cannot see it. It cost me $135 to learn that lesson.

 

[18rabbit]

Re: Voltage drop

By any chance, is there any electronics hanging off the [+] wire that goes to your instrument panel? Anything like fishfinder, GPS, stereo?

 

[jlinder]

Re: Voltage drop

Forgot to mention that you can, for testing only, just lay out a wire and carefully clip it in parallel to the wire from the battery to instrument panel. <br /><br />If the voltage drop goes way down you could have the bad crimp connections IBNFSHN mentioned.

 

[Boatin Bob]

Re: Voltage drop

Rick...if you do go with the relay you mentioned make sure the points are capable of carrying more than your maximum load (allow for expansion) instead of a relay though why not just a heavy duty battery switch?

 

[chuckz]

Re: Voltage drop

JackL forgot to tell you, you have to make the voltage drop measurements with the load turned on. Turn on the equipment that was on when you noticed the problem.<br /><br />It sounds like IBNFSHN has a problem with crimped connectors, maybe you need to solder them

 

[rickf1985]

Re: Voltage drop

Wow, all good replies! Ok Dunaruna here is some more info. I did not want to overload the first message but all the replies are helpful and I have already tried a lot of them. Here goes, first my info. I am a master auto and truck mechanic by trade and a boat owner by insanity. Boat info, 1988 Baja 235 force, 330 Mercruiser tied to a Bravo one drive. Most of the drop seems to be in the supply wire with the drop being about 2.3 volts. the ground is about .5 volt. I figured I would replace the stock wires due to the age of the priginal wiring and the fact that it just looks like a poor way of doing things. That is a long run for a ten gage wire to go to the ignition switch and then to the guages witch are daisey chained in line on the power wire. The only accessories on the line are an FM radio that does not work and a fishfinder that is not installed at this time. The only loads are the engine harness feeds, ignition sendors, etc.. This was tested without the blowers on. When the engine is running I get 13.5 at the battery and 12 .1 at the volt guage on the dash measured with a dvm. The relay I would be using would have a 30 amp rating so I do not think that would be a problem. the reason for useing the relay is so I can retain all stock functions of the guages and to make sure that when the key is off so is everything else. I agree that crimp connectors are a source of loss but I have also heard somewhere that soldering on boat wireing is also bad, correct me if I am wrong as I prefer the solder method. I only want to do this once and although I fully understand voltage loss and drop on cars and trucks Boats are from another planet so I listen to all replies. I hope I have addressed all the questions you may have and look forward to your replies. Thanks.<br />Rick

 

[jlinder]

Re: Voltage drop

L.I. Chuck,<br /><br />Good catch. Can't believe I forgot to include that.<br /><br />taz - the feedback is good. I think you have it when you say the drop is 2.3 on supply and only .5 on the ground. If they are the same guage they should be the same. Look for problems with the supply wire.<br /><br />If the wiring is old, hacked up, you might want to just replace it. 10 ga does not sound that bad, but I do not know the total amperage of all your accessories, or the length of the wire.<br /><br />When you fix or rewire, make sure it is a good crimp and you seal it with heat shrink to prevent corrosion.<br /><br />You CANNOT use solder as the only method of making a connection. Boats really vibrate.<br /><br />There are heated discussions on whether you can/should solder after you crimp. I am a strong proponant of not soldering, but to be fair if you have doubts read the many posts here and form your own opinion.<br /><br />Please continue to give us feedback. It is really helpful, and helps everyone who comes across a problem like this. It's a great way of giving back to the forum.

 

[Richard Petersen]

Re: Voltage drop

NO connections are soldered in the military except for printed circuit boards. Any vibration kills the solid end of the solder and wire strands there.

 

[chuckz]

Re: Voltage drop

Cyclops2,<br /><br />You've never looked at a RF connection have you? There are long discussions on solder versus crimp. Your information and conclusion is wrong. Soldering is used routinely in military and aerospace applications when appropriate.<br /><br />taz1985,<br /><br />JackL is correct, you cannot use solder as the sole means of connection. A proper solder connection includes a splice first. Either crimping or soldering will work IF DONE PROPERLY. If you're not a trained solderer, buy marine grade crimps and the proper double crimping tool.<br /><br />Ten gauge wire can handle thirty amps with no problem. Use heavier gauge wire if you want. Make sure it is stranded wire and rated for marine usage. Also make sure your support the wire between the battery and the helm.

 

[rickf1985]

Re: Voltage drop

Ok Guys, Crimping wins! I just thought of a flaw in my relay circuit idea that I am surprised none of you caught. If I run 10 guage hot up front to a relay and trigger the relay off of the original hot wire I am effectivly eliminating the 50 amp breaker back at the engine. WHOOPS! I am going to see if I can track down where I am loseing the voltage in the hot wire. I did not check the connections at the breaker and they look like they have never been cleaned. Of course I decide to do this after the rear seat and interior are back in which OF COARSE covers the area I need to get to!!!! Damn I love working on boats, I'll show that arthritis who's the boss! OWWWWW<br />Rick

 

[Boatin Bob]

Re: Voltage drop

Rick...you said you were going to replace the stock wires with the new ones so we all assumed you would run new ones from the 50 amp breaker up to the front (relay)

 

[rickf1985]

Re: Voltage drop

I figured that was the case, I'm just bustin! I was under the gunwall and checked out the wire from end to end and there are no splices so I am going to check all the ends for the nasty green stuff. I am thinking the connections at the breaker are most likely where I am going to find my problem. If so I am going to just replace the one wire. Thanks for all the help and I will let you know what I find.<br />Rick