Steve, in a situation like this, I'd probably try to draw a schematic of the system in question. Then we could estimate the wire sizes and lengths. Might be able to calculate that 2 volt drop, if we had a good idea of the current load of the fan. So far, you've presented the best explanation of what's going on. Thanks! It would be fun to point a temp gun at the wire in question.
Would also be nice to know what the fan is rated at for amp draw. As stated earlier Spal brand can draw to where the recommended fuses are 40 amp. If it's a large amp drawn fan I would think the wire size for the 12V constant should at least be 10 gauge or greater depending on how long it is. Just got done curing two cars problems in the last month that were fan related. When the fan turns on, wait a couple minutes and put your hand on the switched 12 volt wire and then the constant 12 volt feed wire for the relay and see how warm/hot they feel. If their overly hot, probably too small of gauge wire for the draw of the fan.
I don't know how much fun it would be, but it would be enlightening... This is a serious problem; 15% is a huge drop, particularly in a main 'feed' circuit. I did some playing around on my voltage drop calculator, and assuming a #10 feed wire from the battery and a 5' length, you need a 400 amp load to get a drop this big. The actual load can't be this high, so this points to there being a 'point' problem; a splice or connection that's having a hard time carrying the current/voltage when the fan is on, maybe loose or improperly done. That this would be a 'hot spot' there is no doubt. Now, I 'assumed' a wire size/length; double the length of the wire, and the needed 'load' to produce that voltage drop goes down by half. Having a schematic of the actual system with sizes and lengths would be a huge help, but I suspect that would require some serious tearing into the harness to figure it out. In any case, this needs to be addressed; this is the kind of stuff that can burn cars to the ground...
How about 15' of #12 wire? 30 amps would give a volt and a half drop. My guess is the power comes in to the fuse block, then back out to the fan relay. Some poking around with a hand held volt meter, measuring voltage across different parts of the circuit, should give an idea what's going on.
Like I said earlier, tracing out the wiring circuits is a pain in the ass, but well worth the effort in the long run, as your knowledge of how that part of the car is expanded, and you end up with a schematic you can use to troubleshoot and diagnose problems like this one. Someone is going to have to at least trace out this fan circuit to get it properly corrected.
Well, if the main fuse panel feed is #12, somebody seriously dropped the ball on the harness design. I'd bet money that's what he has. As to tracing the wiring, I agree that it's a very good idea but the practicality of doing this is sometimes not so easy. The penchant that some builders have for running the wiring then gluing insulation and carpet over it all can mean that you have to trash all this to get at it. I really need to get busy and finish my 'Wiring 101' thread as this is the sort of stuff I was going to address in upcoming installments....
If it's just a long run of slightly too small wire, then it's probably not a hazard. That's why I'm not too concerned about it. But without being able to get our hands on the car, it's all just pissin in the wind
I didn't read every post and it may sound dumb, but did you check the belt tension? Could it be slipping under high load.
Being your not fond of a fan, so maybe there is some apprehension. I particularly don't care for them either. I must admit though, I have one on my Shoebox 12v system. It was there when I bought it. Said I was going take it off more than once. It's still on there. Mine kicks on when temp rises to 220 degrees (adjustable thermostat) and volt gauge does drop 1-2 volts at idle. It increases again when I give her the gas. I think your good to go, enjoy your new ride.
A 15% drop is a LOT so it should be something to be concerned about, at least until it's proven to be benign. Like I've said, electricity can be funny stuff. One guy will have the nastiest rats-nest of badly-done wiring you've ever seen and have no issues for years, some other guy will make the effort to get it right but make one mistake and burn his car down... You never know. But it's rare to get a warning, so I always heed them....
He said it reads correctly when the fan is off, so there's definitely an issue with the fan circuitry or power to it.
Mr. HRP, Question for you. How long has the 32 been wired and running Okay with this wiring the way it is? Would the answer to this help identify a critical problem, or possibly something that is not as critical. Crazy Steve is concerned for all the right reasons, but if it has been good for years? My electric fan on my 32 does pretty much the same thing, but it keeps charging, and starting and working okay. I wish I could add something better to help. I did not build and wire my 32 either, and wire tracing would be a nightmare. Keep us posted because I am very interested in the outcome. All the best with this.
Well, just my story to share, on my Camaro several years ago, I fired it up and the factory gauge stayed at about 12-ish volts, crap, went and got a new Alt for it...same thing...checked at the battery while running, right around 14 volts, like the gauge used to read....volt gauges can get finicky...I'd at least check it out..kinda like oil pressure problems, like every one will say "verify it with a mechanical gauge".
Steve, I know you are probably tired of repeating yourself over and over and tired of trying to rephrase it in different ways, but DON'T STOP! It takes a while to beat it through our thick skulls.
Danny, my Deuce roadster has the biggest electric fan I could buy, behind an aluminum radiator. The motor is nearly 3 1/2 " deep. When the fan kicks on, the voltmeter needle drops maybe a quarter volt, and with a/c and headlights working, it shows about 12 3/4 to 13 1/4 volts, and stays there until I stop. My alternator is a 140 amp unit from Vintage Air. The volts don't return to 14? while I am at 70 mph, but I have a 700R4, and at 70 I only taching 1950 rpms. I think it should be enough to keep the battery up, although some buddies say I should be reving higher in order to keep everything charged. I don't think so, but whatever. I would rather have a good old fashioned steel fan mounted to the water pump and a good shroud. I see no reason why anyone would want an electric fan if there is clearance to run the real thing.
My Deuce roadster has an American Autowire kit installed by a friend who has used them in every ride he has built in the last 10-15 years. I think the wiring and gauge size are correct.
At 70 MPH does the fan have any load at all? It seems to me the wind would negate anything the fan had been doing.
They may be correct for the particular cars he's wired; that doesn't guarantee they're right for every application....
Aw, shit, squirrel. You just want to get that nice sedan and drive Hell out of it. DON'T FALL FOR THIS FUCKIN' SHIT, Danny ! ! !
I've been driving the sedan..a lot around town and on the interstate. I've put almost 500 miles on the car and only use the fan when the temperature creeps up in traffic,so far no problems. HRP
I agree with the relay and wiring size. if it was wired through the overtaxes harness you will see voltage drops. Those fans draw a lot of current. Try and isolate that circut from the stock harness.yruhot
How does inadequate wiring to a radiator cooling fan effect the alternator output or voltmeter reading?
There's multiple scenarios that could cause this, for a theory lesson go here: http://www.jalopyjournal.com/forum/threads/wiring-101.843579/
One wire or three wire alternator? http://www.madelectrical.com/electricaltech/remotevoltagesensing.shtml http://www.madelectrical.com/electricaltech/onewire-threewire.shtml
At 12 3/4- 13 1/4 volts the battery is not charging. You need to be at least 13.2 volts to be over the "overcome voltage" in a 12v volt battery to allow it to charge.
The Jalopy Journal
