Bullnose Enthusiasts Forum

DIY voltmeter

Classic

List

Threaded

17 messages Options

Lima Delta

DIY voltmeter

After spending some time recently troubleshooting a charging problem in the freezing cold, I've been thinking about a 3G swap... If I were to go ahead with this upgrade, I would like to have the ammeter function as a voltmeter. I've considered the RCCI voltmeter conversion but I can't help but wonder if it isn't something I can do myself, and whether or not anyone else has had success making a DIY conversion?

I understand the general theory of converting an ammeter to a voltmeter, but I need to figure out the particulars. I have three spare ammeters to play with, but I don't want to waste any by making avoidable permanent mistakes. I also have a friend who works at an avionics shop that can test the ammeter with a variable power supply to determine it's specifics so that I can work out what kind of resistor to add. Can anyone tell me whether or not the RCCI converted units have any external modifications at the back of the gauge, or was it all done internally?

Lucas

Lucas
"The truck" - 1985 regular cab F250 4x4 - 351W HO, C6
"Beige Beast" (project) - 1981 regular cab F250 4x4 - 300 straight six, T18

Gary Lewis

Re: DIY voltmeter

Administrator

I saw no external mods on my ammeter converted to a voltmeter.

As for what it would take, I think you could do it with a resistor in series - except that the ammeter's needle rests in the middle of the scale. But if there's an easy way to make it rest at that left edge then the resistor trick should work.

I did some testing on four ammeters and recorded the results on the page at Documentation/Electrical/Ammeter. But here are the results. As you can see, it only takes about .25v to make it go full scale, assuming starting at the left edge.

If you assume the meter is a .17 ohm resistor and put it in series with an 18 ohm resistor the combination will pull .79a at 14.4 volts. And the drop across the meter's .17 ohm will be .135v, which is about right to take the thing to half scale.

Please let us know what you find!

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

Lima Delta

Re: DIY voltmeter

Thanks Gary,
I did see your numbers earlier, and the variation was what got me thinking I should test my own to see how it compared.
The photos I've seen of what I presumed to be unpowered converted gauges (like the one on the RCCI site) also had me wondering because they've all seemed to show the needle resting in the middle. Is this the case with your voltmeter, or does it in fact rest to the left?
If do this myself, my plan will be to do like you've suggested: somehow modify the gauge so the needle rests to the left, then add the appropriate resistance. I'm curious to open the case and see how much space there is inside.

Cheers,
Lucas

PS It's been said before I know, but you've done a real service by setting up all these resources. Thank you!

Lucas
"The truck" - 1985 regular cab F250 4x4 - 351W HO, C6
"Beige Beast" (project) - 1981 regular cab F250 4x4 - 300 straight six, T18

Gary Lewis

Re: DIY voltmeter

Administrator

Welcome! Glad it is helping.

My voltmeter rests to the left just like the other gauges when off. So if you can get it to rest there then the resistor trick should work very well.

There are plenty of 40 ohm potentiometers available, some that have 22 turns, which would you let you dial any ammeter in so the top reading would be what you want.

Gary, AKA "Gary fellow": Profile

JimsRebel

Re: DIY voltmeter

In reply to this post by Lima Delta

Lima Delta wrote

I have three spare ammeters to play with, but I don't want to waste any by making avoidable permanent mistakes.

Lucas

He will buy your cores. So it's really a freebie for you. Just mail all 3 to Rocket Man, assuming all 3 are usable, let him keep 2 cores and convert one for you.
When I did it I mailed in 2 cores, just in case 1 wasn't usable. He gave me credit for the other core, so for me it was almost free. I also bought the orange needle paint from him and paint all the needles to match.
Jim

1986 F150 XLT Lariat 4x4 300 C6, 9 inch 3:50, 235-15 tires, sway bars and skid plates, DS2 dist with GM 4 pin IGN module and no computer. still using the feedback carb; 3G ALT swap, PMGR starter; 150,000 miles, 2nd owner

JimsRebel

Re: DIY voltmeter

Here is a link to some testing I did about 10 years ago on the amp meter.
https://www.ford-trucks.com/forums/1122070-replace-amp-meter-with-dvm-update-with-photos-2.html#post11204855

This was before I knew about Rocket Man Voltmeter. He replaces the guts of the meter and does not reuse the stock meter movement. The nice part about his voltmeter is it only reads the voltage in the range you need, compared to a 0-20 volt scale. More info in the link below, encase you haven't read it yet.
https://www.ford-trucks.com/forums/1339746-how-to-swap-amp-meter-to-volt-meter.html

Jim

Lima Delta

Re: DIY voltmeter

Hi Jim,
Thanks for the advice. I may end up going with a unit from RCCI in the end, in which case I'll send him two cores (pretty sure he won't buy the one I started playing with last night lol).
I was able to modify the movement so that the needle wants to rest to the left now. I removed the "U" shaped magnet that keeps the needle centered and replaced it with small magnet on the left side. Getting the placement right was a bit tricky but I've got it all tacked back together with hot glue for now and it looks pretty good so far. I wish I had my own power supply.

Lucas

Lucas
"The truck" - 1985 regular cab F250 4x4 - 351W HO, C6
"Beige Beast" (project) - 1981 regular cab F250 4x4 - 300 straight six, T18

Gary Lewis

Re: DIY voltmeter

Administrator

Changing out the magnet and getting it to rest on the left is a big step. Now if you can map out what voltage/current it takes to make it hit the various marks you can figure out what resistance to put in the circuit.

But a variable power supply is ideal for that. I found mine on Craigslist years ago for $35 and have used it extensively. The ability to bring the voltage up slowly from 0 is a huge help.

Gary, AKA "Gary fellow": Profile

Lima Delta

Re: DIY voltmeter

Gary Lewis wrote

But a variable power supply is ideal for that. I found mine on Craigslist years ago for $35 and have used it extensively. The ability to bring the voltage up slowly from 0 is a huge help.

Yes, now including a scan for a decent used power supply in my morning rounds through fb marketplace lol.

L

Lucas
"The truck" - 1985 regular cab F250 4x4 - 351W HO, C6
"Beige Beast" (project) - 1981 regular cab F250 4x4 - 300 straight six, T18

Gary Lewis

Re: DIY voltmeter

Administrator

In the interim you could put a pot from your battery to the voltmeter and slowly turn the pot up and record the voltage shown on your DVM at the voltmeter when it moves.

Gary, AKA "Gary fellow": Profile

6.9-250

Re: DIY voltmeter

In reply to this post by Lima Delta

Shipping is high for me to send mine in for the conversion from Canada to US and back so I decided to try on my own. I purchased one from Canadian Tire and disassembled it. I wanted to retain the oem look so I cut the needle off of the ammeter, cut the one off of the voltmeter and glued the factory one on. It took a lot of messing around to fit and mount it. I installed it so when the truck is running at full voltage, the needle was slightly over the last line on the right side of the ammeter display.

In the end it turned out great....would I do it again...not for the price you can buy one in the US for, lol.

The meter I used was ..EQUUS 2" BLACK VOLTMETER E6268. It was a cheap meter so I had nothing to lose.

1985 Ford F-250, 6.9L, Auto C6, 4x4 208F, Extended Cab

Gary Lewis

Re: DIY voltmeter

Administrator

I would ask for a pic, but I'm guessing you can't tell if from a stock ammeter. Right?

But did you take any pics along the way of the internals? And how you mounted it? If so those might be helpful for others.

Thanks.

Gary, AKA "Gary fellow": Profile

Lima Delta

Re: DIY voltmeter

In reply to this post by 6.9-250

6.9-250 wrote

Shipping is high for me to send mine in for the conversion from Canada to US and back so I decided to try on my own.

Yeah, I'm in the same boat. The shipping is a bear these days. Like Gary suggested, I'd be interested in any photos of your process.

Still waiting to test mine. I'm wondering if the magnet I used is too strong...

L

Lucas
"The truck" - 1985 regular cab F250 4x4 - 351W HO, C6
"Beige Beast" (project) - 1981 regular cab F250 4x4 - 300 straight six, T18

6.9-250

Re: DIY voltmeter

In reply to this post by Gary Lewis

Sorry, I did not take any pics during the install. Definitely dropping the ball on that one.

Only way to tell is that the needle is not sitting in the middle anymore.

1985 Ford F-250, 6.9L, Auto C6, 4x4 208F, Extended Cab

Gary Lewis

Re: DIY voltmeter

Administrator

Looks great! What voltage range does it have?

Gary, AKA "Gary fellow": Profile

6.9-250

Re: DIY voltmeter

Thanks.

Voltage range is same as on the Equus meter. The sweep range on the Equus does not match the range on the ammeter. I was not concerned with that though. I just wanted to know if my voltage was dropping below 14 when running. So I mounted it so that 14-14.4v was near the last mark on the ammeter. When its off, I think the needle drops out of sight range. I used an ignition line for voltage off of the main harness below the steering column ( to the left side of the steering column I believe).

While the cluster was out, redid the needles with hipo paint. Gave 2 coats or so. What a difference.

Fluorescent Speedo & Gauge Needle Restoration Paint HP-FLORP-01 1

https://www.hipoparts.com/fluorescent-speedo-gauge-needle-restoration-paint/

1985 Ford F-250, 6.9L, Auto C6, 4x4 208F, Extended Cab

Lima Delta

Re: DIY voltmeter

Looks good. I notice the illumination to the right side of the tach on your panel is much brighter than on my panel... I replaced all the bulbs with LEDs a while back. I guess I should check to make sure they're all working.

Lucas

Lucas
"The truck" - 1985 regular cab F250 4x4 - 351W HO, C6
"Beige Beast" (project) - 1981 regular cab F250 4x4 - 300 straight six, T18