An amp guage in a car, reads from the center. Left is discharge current, right is charge current. A voltmeter gauge usually reads from the left. Left is zero, right is some number higher than 14 volts. Amp meters aren't used much anymore, because alternators are so powerful. Most meters read 60 amps or less, and newer alternators are above that as a minimum. I'd recommend just leaving it in the cluster, but disabling it (don't hook it up). Put a voltmeter in the glove box or something.
So, Bruce, (I know Flat Ernie has mentioned this before) if you convert a 40 to 12V will it read off the scale? is there a known value of resistor to get a reasonable indication from a 40 battery meter? Cheers! Mart.
Don't think a resistor is right approach--those are load based, hardly any load on this... A voltage regulator type converter perhaps?? Would that read proportionally over a reasonable part of the scale?? Dunno. An old 6-12 swap kludge was center tapping the battery for 6V needs--probably not really doable on modern hard shell batteries, and of course would not respond if a cell croaked in other half...this is the HAMB: Someone here has confronted this problem and licked it...
I've confronted the problem but couldn't bring myself to lick it. The standard voltage drop does not 'properly calibrate' the BATT gauge. Normal operation is in the yellow and it acts kinda funny, reading really low sometimes (I have a modern gauge too so I know what's really going on). I think it was Flat Ernie that hypothesized that a 60Ohm resistor would do it. Don't know that anyone's tried it though. It is also possible to change the zero and span on the gauge which I think would correct the 'yellow' problem. I have no idea what to do about the 'funny' problem. Anyone else?
OK I'm not Bruce but a Volt meter is a volt meter it reads voltage it doesn't care what the rest of the system is calibrated to run on it still just reads voltage.
This is why I like '32's rather than late models like this--high tech electronics hurt my head. It won't help here, but here are all the steps necessary to conver a set of deuce gauges to 12V, and the parts list:
i used `40 gauges on 12 volts and used a runtz voltage drop like speedway sells on all the gauges. the volt gaude would read the same value regardless if the alt was charging or not. switching to a 60 ohm resister on the volt gauge it reads straight up when the ignition is on and the motor not running/alt charging..when you start the engine it reads a little higher, so you know it's charging yes, it's true..a volt gauge is a volt gauge...but 12 volts pegs the needle
So if I understand correctly, you have it like this? 12V+ ---- 60 Ohm resistor ---- BATT gauge ---- ground
When converting to 12 v. I did install a RonFrancis Black Box to reduce voltage to gauges to 6v. The needle in the BATT gauge remains in the middle and never moves so I am wondering why. thanx.
I think the RF box is an electronic regulator that will put out 6-7V from anything above that, so it won't register change til a 12V battery is well into the dead phase. Your fluctuation with a good bat would be from 12-14, and something around 12 would be the start of bad news on a running 12V car. So that's the crux of the problem--the ideal would be a gadget far beyond my comprehension that would accurately halve the voltage, making 10-14 read 5-7 roughly. Maybe a very slight variant of that resistor would ballpark the gauge...I don't think it is a theoretically right solution, but if it makes the needle move between fair and good that sounds like a tolerably good state of affairs.
Reminder to self: Go home and polish the hand crank, install magneto, and convert lights to kerosene on deuce--this electric is more trouble that it's worth.
You have to divide the voltage in two. For starters use a flashlite battery or two to make the circuit test voltage. You have to put two resistors in series between pos and neg, and big enough to not have too much current or power in watts. between the two resistors should be half voltage. Now the fun part, When you place the meter in the center to either end the resistance of the parallel resistor now appears to be half what it was. So to correct you'll have to maybe add one in series with the meter to buck that up a little. I'm saying this in generalities so if you do the math you can solder a couple of 50 cent parts together to put the meter up.
A '40 "BATT" gauge is an ammeter which reads AMPS. It only reads amps and does not care what the battery voltage is. Apm gauges are usually installed in the small wire that goes to the battery. They are designed to read the "flow" of current to or from the battery. If you install an amp gauge it is tested with the engine not running: Turn on the ign, observe gauge. It should read close to 0. Turn on headlights. Gauge should swing to discharge or minus side.
Just found a '40 diagram in the linited stash of books concealed in my office... original meter wiring is just a strap to next adjacent gauge to reach system voltage, then a strap to ground on the instrument cluster. If this was an amneter, the '40's would all have burnt to the ground as they rolled off the ***embly line, obviating the need for this discussion.
Just saw this post. It is not a true voltmeter, nor is it an ammeter (although all modern gauges are really ammeters at heart! Too in depth for this conversation though). It is just like the rest of the early Ford gauges & uses a bi-metallic strip to move the needle through a gear-train. It is calibrated so at certain voltages, the needle deflects only a certain amount. If you look in the early Ford Service Bulletins, it actually calls out the resistance for the Battery Meter at 60ohms. It then gives fine tune calibration adjustments for each band. I don't have it handy or I'd give 'em to ya here. If you use a CVR, it will ALWAYS provide 6V to the gauge, so the needle will NEVER move. It will sit in the middle (probably the lower part of the yellow band). This is because the C in CVR means "constant" - you get a constant 6V regardless of whether or not your alternator or 12V generator is putting out 12V or 14V - 6V comes out the CVR. You want that same gauge relationship - yellow at about 12V & green band at about 13.5V & Red above 14V (just guessing). You accomplish this by doubling the resistance wired in series with the gauge. Since the Service Bulletin was kind enough to give us the resistance for this particular gauge, you can install another 60Ohm resistor in series with the gauge & it should work reasonably well. A caution on "radio shack" resistors - the tolerances on resistors vary wildly, so check them out with an ohmmeter to ensure you're actually getting 60ohm out of them. I use a small potentiometer to calibrate mine - hook up a digital voltmeter to your battery to see what's going on & adjust your potentiometer to make the gauge read what it needs to read. I've probably over-explained again & managed to confuse the issue... EDIT: Found my service bulletin book. You should have the following colors from left to right - red, orange, green, red. (I guess the orange on mine is faded to yellow) Top of first red range/bottom of orange range = 6.2V Top of orange range/bottom of green range = 7.1V Top of green range/bottom of second red range = 8.25V If doubled, these might be slightly high at 12.4, 14.2, & 16.5 respectively - I'd probably use a potentiometer & tweak it to be 12, 13.5 & 15 - or as close as I could get to those figures... BIG NOTE: I haven't done this yet, but have more than just a working knowledge of electrics/electronics... 2nd EDIT: Found that they used these in some '39 as well (probably Deluxe models), but have letters instead of colors. Here's what the gospel says about those: N = 6.75-8.25V H = "in excess of 9V" 3rd EDIT: Just put some 12V field coils in my generator & got my 12V voltage regulator hooked up. Need to get a 12V battery & sort the gauges out - will be using one of Mart's CVRs for fuel, temp, & oil. I'm going to set a potentiometer to 60ohm to start with & wire it in series with the battery meter. Got new bulbs to stick in too. Will let everyone know how it works out. Still battling some minor ignition woes, so can't crank it up just yet - parts will be here Monday. Hope to get it sorted Tue.
OK - did the 12V conversion today. NOS 12V field coils in the generator, a new VR, bulbs all around, one of Mart's CVRs for oil, temp, & fuel and I adjusted a small potentiometer to 61.2 Ohms & wired it in. I don't have a 12V battery yet, but I used my portable jump-start thing (you know, charge it up - keep it in the trunk) & had 12.85 volts & my Battery gauge was near the bottom of the orange zone, so I adjusted the potentiometer to put it about 2/3 through the orange zone. Once I get it running again (did battle with my distributor & am in the middle of converting to a crab-style), I'll update you with various voltages. I just used a very small 0-125 ohm potentiometer & epoxied it to some phenolic block so I could mount it w/o worrying about it shorting out. Also got electric wipers now too!
Cool. Any chance you could put a meter on the pot now that you have it set and get back to us with a target resistance?
Personally, I'd recommend a pot for everyone - start at 60 & adjust to what works for you. Two primary reasons - resistors are rarely their stated resistance - unless you buy precision wire-wound type & each install will have small variations that could be an ohm or two anyway. I seriously doubt I moved it more than 2-3 ohms based on pre-install testing. The real take-away is that 60-ohms is the correct value as found in the Service Bulletin. If you can find a 60-ohm resistor, you're probably "close enough" I will see if I can disconnect one side & measure it though...
After reading this thread, it would seem that your question has been partially answered. VOLT METERS - measure the volts in the electrical system. Usually have two SMALL terminals on the back; and are usually connected to the nearest source of electricity in the wiring. (e.g. - connected to an ignition switch) THEY ARE POLARITY SENSITIVE. (pos. to pos.; neg. to neg.) There ARE some gauges that were "self grounding" - meaning the case of the gauge acted as one side of the hook-up. (if your changing polarity; this type of gauge CAN'T BE USED!! ) In early Fords; they were intended to read from "0" to around "8" VOLTS. They often didn't have numbers; just a RED to YELLOW to GREEN face plate. One strange thing that Ford - and I believe a couple of other manufactures - did; was to mark the FACE PLATE of their VOLT meters, with the term AMPS ever though in fact they weren't AMP gauges. When I was taking auto mechanics back in high school; I asked one of the instructors WHY they did this?? He told me that people were SO used to the term "AMP", that they made such a fuss when "VOLT" showed up one one gauge, customers requested it be removed, and an "AMP" gauge be installed. Rather than re-wire the car, Ford dealerships just replaced the "VOLT" gauges with one that had "AMP" marked on the face! (most people never noticed any difference!!) As discussed above; a means of VOLTAGE DROP is needed to keep from "blowing" the VOLT gauge out of the dash - ***uming your converting to a 12 VOLT system. (Flat Ernie's method is one way) AMP METERS - are used to measure CURRENT FLOW. (draw in "dis-charge; "Charge" in charging conditions ) They will have LARGE TERMINALS on the rear. (and sometimes what looks like a strip of copper bridging between the terminals - that's used for a "fixed" load.) Almost EVERY electrical component in the vehicle would be wired to one side of an AMP gauge. (heavy gauge wire coming and going from the gauge) Although AMP meters are supposed to hooked POS. to POS., etc.; they WILL work if installed backwards. The gauge will just read backwards. (showing discharge when if fact it's charging, and visa versa. As noted above - Early AMP gauges were only good for around 60 AMPS; so using an early gauge with a high output alternator would likely "fry" it if high "draw" or "charge" situations occurred.
Good info, Dave. To expound a bit - the early Ford Battery meters are effectively voltmeters, but they do not measure the voltage directly - they rely on a sending unit. That sending unit is the internal resistance of the gauge itself - as mentioned, Ford provides this info. Nearly all modern gauges are really ammeters - even your voltmeter is an ammeter. They use variable resistance to change the current through the gauge & deflect the needle based on the inductance. The early Ford gauges are unique electro-mechanical devices and are all technically ammeters as well, but their sending units don't vary resistance like modern gauges do, instead they regulate current. It's an unusual setup, but one that works reasonably well. The only exception is the battery meter. It regulates current through itself based solely on its internal resistance - hence my choice to make it work on 12V by doubling the resistance is, I believe, the only reasonable way to convert it to 12V for the average enthusiast.
Flat Ernie and all those who contributed, THANK YOU. I found the owners manual and here's what it says: In the original 1940 FORD owners manual it says on page 16: "The Battery Gauge indicates the voltage of the battery and generator circuit. It is a protection against damage in the event of failure of the generator or regulator. The pointer should not at any time read above the green sector. After turning on the ignition switch and before starting the engine, the pointer should rise at least to the orange sector if the battery is fully charged. In the evnet the indicator fails to reach this point after waiting approximately one minute, have your dealer check the condition of the battery. Under normal driving conditions and with no load except the ignition current, the pointer should rise to and remain within the green sector."
AHHHH,dug this up, I have a 47 ford converting from 6v-12v and looks like it is the ******* v-amp meter Batt gauge.My question is ,why bother with it if it does nothing with a 60 ohm resistor and converting gauge to volts is improbable wil never read until batt reachs 6 v. Converting to true amps burns the car down and who cares how many amps you are useing at any giving time Seems like best way would be to put a idot light in and by p*** and leave for static display. Im confused. May be best way would be to use 2 6-v batteries in series and tap off 6-v side ,might work and save on voltage reducer to gauges.What do you think.
1947 will have an ammeter - not a batt gauge like being discussed here and used on 39 Deluxe and 40 models only. Do not put a 60 ohm resistor inline with your ammeter. The 60 ohm resistor is specifically for converting the 39/40 BATT gauges to 12V. These are the only two gauges that conversion will work for. An ammeter will not burn your car down. You've got an ammeter in there currently - is your car burned down? You care, not so much about specific amperage (normally), but that your generator is putting out more current than your system is using. If not, your battery is discharging. Think of the + side of the ammeter as "charging" and the - side as "discharging" and it'll make more sense why you'd use an ammeter. If I were building a car from scratch & didn't care what "style" I was building to, I would use both an ammeter and a voltmeter - each tells you something slightly different, but both are useful to monitor the health of your charging system while rolling down the road... Your ammeter requires no conversion to work on 12V. Run it.
No. The 60ohms was pretty darn close to right on the mark. I know I fiddled with it - back & forth a couple times just tweaking, but as I mentioned, I doubt I moved it an ohm or two either way based on the pot itself (IIRC, it took 4 turns to change one ohm). If doing it again, I'd probably just stick a 60ohm resistor inline & be done with it...
The Jalopy Journal
