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-   -   Ammeter Overcharging (http://www.clubcobra.com/forums/ignition/143417-ammeter-overcharging.html)

xb-60 03-29-2020 07:23 PM
Quote:
Originally Posted by patrickt (Post 1474065)
Or run a parallel wire with the ammeter circuit.....
Now that sounds simple. Did you come up with that solution yourself, or is that an accepted way of 'insulating' your ammeter?

I will be using a Smiths 30 amp ammeter on my 289, as that is what the original cars used. I was a little uneasy about using a 30 amp ammeter, but your method would help my ammeter cope quite safely.

Cheers,
Glen

patrickt 03-29-2020 07:32 PM
Quote:
Originally Posted by xb-60 (Post 1474078)
Now that sounds simple. Did you come up with that solution yourself, or is that an accepted way of 'insulating' your ammeter?
That's a pretty common way of reducing the current passing through an ammeter. Really high-quality, high-amp gauges don't need it, but I would not bet my car on the quality of one of these old Smiths gauges. :cool:

xb-60 03-29-2020 07:54 PM
I completely agree

HighPlainsDrifter 03-30-2020 09:27 AM
generators used them
 
Hi,
The old cars with generators used ammeters, new cars with alternators should only use voltmeters. DC current is dangerous and if shorted or not wired correctly will BURN down your car. Most cars use 80 amps to run things;
electric fan 25 to 35 amps, lights, 8 amps, ignition 5 to 30 amps for MSD, heater 20 amps, etc 'that is why you have a 100 or 140 amp alternator.
The point is don't put all that through a 30 amp gauge, you can over heat and BURN your car down.
I have worked with DC in the phone industry for 35 years and have seen shorts arcing and welding big ironwork without blowing a 60 amp fuse.
Perry:cool:

fastd 03-30-2020 09:53 AM
Quote:
Originally Posted by patrickt (Post 1474065)
Or run a parallel wire with the ammeter circuit. I have a 12 gauge parallel wire with my ammeter circuit and it does two things: 1) It mutes the heavy draws of current when my fans come on, that used to send the needle all the way over to the left where it would get stuck, and 2) it dynamically re-routes current around the ammeter (which I really like) should the ammeter start to overheat. The ammeter still registers correctly, the readings are simply reduced. They don't, of course, reduce past the zero mark and give you an incorrect direction of current.:LOL: But, it pretty much eliminates the possibility of the ammeter overheating because, as the ammeter heats up because of a failure, it creates additional resistance in that leg of the circuit and current will then just go down the parallel path (that's just Ohm's Law). Think of it like having two parallel wires, of equal gauge, running to a 120 watt light bulb, which will draw roughly ten amps. All things being equal, each wire would have five amps on it. On one of those two wires you have a 20 amp fuse, and on the other wire you have a one amp fuse. You will not blow the one amp fuse because, as the filament heats up, the resistance increases and the current then passes through the other wire. :cool:
For those of us that don't know electrics as well as we should; could you explain a bit more granualarly how to run a parallel wire?

fastd 03-30-2020 10:58 AM
I called holley. They say that the efi ecu pulls 6 amps but the fuel pump pulls about 15 amps; so 21 amps plus what the battery pulls would be my +25 or so.

They didn't entertain the idea of pulling power through the fuse box cause it could create "electrical noise"; I can see that with respect to the ecu but I think if I power the fuel pump through the fuse box I could solve most of my issue...thoughts?

patrickt 03-30-2020 11:21 AM
Quote:
Originally Posted by fastd (Post 1474096)
For those of us that don't know electrics as well as we should; could you explain a bit more granualarly how to run a parallel wire?
Different cars will have different "easy ways" of running a parallel wire. But remember, the goal is to have a shortcut path from the alternator to the battery without going through the ammeter. That said, the easiest way that will work on pretty much all forms of cars around here is to run a wire from the output terminal of the alternator to the positive terminal of the battery. Once you've grasped that concept, you can look at your car and say "instead of wiring it directly to the positive side of the battery, I'll wire it to the positive side of the starter solenoid that I can clearly see connects right to the battery." Likewise, you might say "instead of connecting to the output of the alternator, I'll connect to where the alternator output wire clearly connects to the fusebox." Each car will be a little different, but that's the basics. On an ERA car, connecting the alternator feed at the fuse box to the fused side of the 50 amp circuit breaker on the firewall is probably the easiest.


Quote:
Originally Posted by fastd (Post 1474100)
I called holley. They say that the efi ecu pulls 6 amps but the fuel pump pulls about 15 amps; so 21 amps plus what the battery pulls would be my +25 or so.

They didn't entertain the idea of pulling power through the fuse box cause it could create "electrical noise"; I can see that with respect to the ecu but I think if I power the fuel pump through the fuse box I could solve most of my issue...thoughts?
OK, the ECU could be sensitive. MSD essentially says the same thing (run their box right off the battery), and most of us also run a big fat capacitor across the leads to filter out electrical crap like AC, spikes, etc. But I can't see how feeding a fuel pump from the other side of the ammeter would cause any harm at all. But, to be prudent, just run a 10 gauge test wire from the fuse box to your pump and see how it all runs before you make final wiring corrections.

cycleguy55 03-30-2020 01:37 PM
I could be an outlier here, but IMO you should be running a voltmeter, not an ammeter.

https://www.hotrod.com/articles/hot-...ical-system-2/

https://www.speedwaymotors.com/the-t...oltmeter/28744

patrickt 03-30-2020 01:39 PM
But ammeters look cooler.:cool:

fastd 03-30-2020 02:36 PM
I like having both

Anthony 03-30-2020 07:01 PM
Quote:
Originally Posted by fastd (Post 1474100)
I called holley. They say that the efi ecu pulls 6 amps but the fuel pump pulls about 15 amps; so 21 amps plus what the battery pulls would be my +25 or so.

They didn't entertain the idea of pulling power through the fuse box cause it could create "electrical noise"; I can see that with respect to the ecu but I think if I power the fuel pump through the fuse box I could solve most of my issue...thoughts?
Well, I'm guessing the fuel pump, and maybe the ECU, are currently getting power directly from the battery, thus pulling all of their power through the ammeter .

Well, assuming the fuel pump has its own dedicated fuse, I think if you power the fuel pump from the hot feed INTO the fuse box, or at either end of the alternator "Bat" wire, you bypass the ammeter, with power going directly from the alternator to the fuel pump ( whenever the pump relay is closed ) . Then, all the power through the ammeter is only going to recharge the battery. Yeah. I think this may work.

olddog 03-31-2020 06:37 AM
The power coming out of the alternator is AC with a crude rectifier, giving a DC current with a lot of AC ripple. The voltage regulator is basically a fast acting switch that is turning the power off and on to clip the DC voltage off before it goes too high. I would not recommend connecting the fuel pump to the alternator. DC motors do not like AC power.

The battery is a huge capacitor and filters all the noise out. That is why the alternator is only connected to the battery, and everything else connects to the battery.

patrickt 03-31-2020 09:39 AM
Or put a nice sized capacitor across the power feeds right in front of the pump. The capacitor will allow alternating current to pass through it, and back to the source, without going to the pump motor. It will also buffer and smooth out the DC voltage going to the pump itself. If you buy the MSD capacitor, you get a nice mounting bracket with it.;) Now, it's nothing magic, just a 26 Kufd capacitor (that you can buy from Mouser for a lot less). Installing it just takes stripping back two wires and screwing in a clamp. https://www.summitracing.com/parts/m...a/instructions You have other DC motors that sit on the alternator side of the ammeter, like your radiator fans, your heater blower fan, etc. but Holley does seem to want it wired to the battery, so I would use a heavy gauge wire (10 gauge) and clean up the feed with a capacitor, if running it from the fuse box. I do that with my MSD box, even though it's wired a foot from the battery. There are tons of threads on how the capacitor extends the life of the MSD box.

fastd 04-01-2020 07:58 PM
Follow up: running the test wire from the fuse box to my fuel pump solved the problem. Shows about 7-10 amps now. Seems to run fine also. Thanks all.

Jaydee 04-01-2020 09:11 PM
You could fit a shunt near the battery and then run 2 small wires to a amp meter so it doesn't carry the current. I have one on my electric quad bike. JD

Anthony 04-02-2020 12:09 PM
Quote:
Originally Posted by fastd (Post 1474214)
Follow up: running the test wire from the fuse box to my fuel pump solved the problem. Shows about 7-10 amps now. Seems to run fine also. Thanks all.
Excellent!!

patrickt 04-02-2020 01:45 PM
Quote:
Originally Posted by fastd (Post 1474214)
Follow up: running the test wire from the fuse box to my fuel pump solved the problem. Shows about 7-10 amps now. Seems to run fine also. Thanks all.
OK, now you're ready for your next ERA wiring upgrade. Click here: http://www.clubcobra.com/forums/era-...g-upgrade.html

fastd 04-02-2020 06:12 PM
Quote:
Originally Posted by patrickt (Post 1474248)
OK, now you're ready for your next ERA wiring upgrade. Click here: http://www.clubcobra.com/forums/era-...g-upgrade.html
Will do. Thanks

patrickt 04-02-2020 06:18 PM
Quote:
Originally Posted by fastd (Post 1474254)
Will do. Thanks
Or this one: http://www.clubcobra.com/forums/era-...-how-pics.html That's up to you.:cool:

CHANMADD 04-03-2020 01:06 PM
The low current side of the relay ,the switched leads , should run through the fuse box.....( I also have an oil pressure switch..5 lbs of more) in this circuit, the high current..directly to pump from the battery, should have the 40 amp inline fuse in that circuit.


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