Amp guage (1 Viewer)
- Thread starter Papa8
- Start date
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When asking for help year and market is good. No it isn't normal. Do the other gauges act up too? I'd bet voltage regulator - they come in external mounted in the engine bay (black box) and internal to the alternator.
Mark W
Yep, I really don't really care that much I guess.
It *could* be normal. The guages is showing how much current is headed toward the battery. You only have a 40 am alternator on the earlier FJ40s. As you can see by the markings, the ammeter was designed with that in mind so it does not take a lot to peg it.
*If* you have a battery that is not hold charge well and you are not driving the rig much, it may in fact be pushing everything that alternator has into the battery while you are driving, trying to fill it up. The battery may be worse than just "a little weak" and there might be an internal short (in the battery).
If you have accessories (lights?) wired in at the battery, the ammeter is showing the current headed for those as current going into the battery.
Mark...
*If* you have a battery that is not hold charge well and you are not driving the rig much, it may in fact be pushing everything that alternator has into the battery while you are driving, trying to fill it up. The battery may be worse than just "a little weak" and there might be an internal short (in the battery).
If you have accessories (lights?) wired in at the battery, the ammeter is showing the current headed for those as current going into the battery.
Mark...
- Thread starter
- #4
Thanks Charlie. It’s a1976 BJ40 (diesel) originally from Costa Rico. The voltage regulator is external to the alternator on the firewall. I replaced the regulator a couple of months ago but perhaps it isn’t working properly. All other gauges appear to be working fine.
Mark W
Yep, I really don't really care that much I guess.
Your ammeter is a full flow type, not a shunt. That means that ALL the amperage flows through it.. Through OLD wiring, through the firewall, behind the dash and around the engine bay. If you do not have an easily explained draw to account for that much current, then I would carefully check for any signs of grounding or shorting. It would be hard to push 30+ amps into a short and not see some adverse signs very very quickly. But check and make sure. You don't want to fry your wiring or even start a fire because you got lazy.
I'd suggest picking up an inductive ammeter to help to diagnose the problem. Something like what these links show. This is designed to be placed with the back of the unit against a wire and the magnetic field generated will cause the gauge to show the current flowing through the wire.
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Mark...
There is a procedure for adjusting the external voltage regulator. But I think its just to adjust the charge and not charge voltage but I'm not sure. Check the alternator big wire out to battery contact and make sure its not sorta grounding out due to corrosion. Load test the battery and alternator - autozoneout will do it for free or you can buy a $50 tester on Amoron and do it at home.
Just for a light hearted comparison, I am sucking a bunch of current from my ‘75 FJ40 alternator and prior to adding these power pulling devices, my ammeter would peak about 1/2 way between 0 and +30A for 15 seconds or less after a startup and then recover to near 0. Now the electric fuel pump from the Holley Sniper EFI, the ignition box and some lights keep this meter about +15 consistently. Turn on headlights and directional signals and it pulsates +15 to +20.
Nothing I have had over the decades has showed a pinned needle as in your photo
Nothing I have had over the decades has showed a pinned needle as in your photo
I have never seen my 72 peg the meter +- side. I have run extra bright head lights on high, 2 heater motors on high and other cab and external lights.
Just noticed your oil pressure is up there as well… ONLY thinking out loud…is this a 24v truck?
Mark W
Yep, I really don't really care that much I guess.
When everything is wired up correctly (by OEM approach), the ammeter is intended to only show what is going in or coming out of the battery. None of any other loads is meant to pass through the ammeter
Mark...
Thanks Mark, must be something coming out or going back in as it has never gone beyond 1/2 swing and only as a stock electrical demand. As I added more stuff to it, it has never fully returned back towards 0 while running. I believe that fuel pump pulls 15A?
Mark W
Yep, I really don't really care that much I guess.
The regulator controls the voltage. There is no way to change the current output of the alternator. That is literally "hard wired" in.
The voltage of the old mechanical regulators is adjustable. Both the cut in and the max levels. It is a finicky and tedious thing, but it is doable. Way back in the day, I used to run dual OEM alternators with dual external regulators on my '55. I upped the voltage a little bit to get more power out of the alternators. About 14.8-15 volts peak. This gave me brighter lights and faster fan motors ( a little bit) as well as faster charging, but was not enough to start frying anything. I also set the cut in differently on the two, so that under normal light loads only one alternator was engaged, the secondary one only kicked in when the primary was unable to handle all of the load without the voltage dropping just a little bit.Mark...
Mark W
Yep, I really don't really care that much I guess.
Ideally... by the factory approach, all of your electrical add-ons would be fed from a fuse block that is on the opposite side of the ammeter than the battery. The only current passing through the ammeter would be going to, or coming from the battery. In that situation, the lights, fuel pump and anything else would have no effect on the ammeter *except* in the way that the factory intended... if the alternator could not handle the load and the battery was draining to provide the extra power needed, the ammeter would show this.
In the dual alternator setup in my old 55, I actually had three ammeters... one showed the load in and out of the battery, just like OEM, the other two showed the output of each alternator. Did I really need that? Not really... but it was fun to set it up and be able to monitor exactly what was going on.
Mark...
South Texas 97
GOLD Star
I added a cheap digital amp gauge to my 76 FJ40. It’s the type that has a ring on it that goes around the wire you are testing. I put it on several different places, at the battery, on the sniper power wire, and ended up putting it on the wire coming from the amp meter on the gauge cluster. My gauge cluster meter showed pegged at 30A but the digital gauge shows 15-17A. So I was satisfied I was not burning up the wiring.
Now, what was consuming all that current, that will require more investigation.
The ring sensor for the amp meter.
To the right of the sniper screen is the digital amp meter installed
Now, what was consuming all that current, that will require more investigation.
The ring sensor for the amp meter.
To the right of the sniper screen is the digital amp meter installed
South Texas 97
GOLD Star
Testing current draw on the sniper power wire
@South Texas 97 I always wondered what the draw would be on the Sniper wire….was there any place that surprised you with either high or low amperage draw? I may need to try this to satisfy my own curiosity. As I had mentioned somewhere, my 30A needle indicates 15-20 on it’s scale after adding the Sniper and Hyperspark and prior to any of that would cycle to near 0 all the time after a few seconds of idle.
Knowing is so much better than assuming
Knowing is so much better than assuming
