'54 clark fork-lift

[shooter]

I took on a fun little project, The *clutch* for a ’54 clark ForkLift.
Whatever it’s called, it’s function *feathers* the drive, so you can inch up to a skid.
It does this by opening successive relay contacts, adding more and more R in series with the 12V drive.
The make-up for these R’s are quarter sized carbon *washers* ¼” thich, with both *faces* copper-plated, hole in the middle.  Each resistor ohm’d mostly 3ish ohms, 2 R’s in parallel, stacked 8 high (in series), originally.
When I got it, 2 contacts fused together, melted the solder and brass, cracked 2 Rs, with carbon dust and that amazing fried electronics smell.  The failure appears to be the funalic sleeve over the copper terminals (1/4”dia) that should be isolated from the carbon pucks.  The circuit is cabled up with #8 copper.  The only measurement I don’t have is I.

I laid it out, pyle’d up the bad parts, cleaned and inspected the rest, put shrink tube on the terminals, re-assembled the module, final readings were 1ohm in NC mode, as you depress the pedal, contacts open, and R increases to max value of 7.4ohms.  I was able to get 7 stacks, the owner tested it and it WORKED!
Once I get actual current readings I’ll be able, maybe, to spec out a Rheostat.  I gave the owner a 1 time, 2second warranty!   
It was a fun, enjoyable fix.

[Ritchie200]

Haha!  What a cool project!  Those look like the doorknob resistors in my Major!

Jim

[shooter]

look like the doorknob resistors

At first I thought they were insulators, but after handling them, my fingers looked like I just finished one of my carbon-graphite sketchs

wouldn't happen to have a source for compressed carbon?

[PRR]

Motor controller. Inching pedal. The other model of my tractor had it (but hydraulic) for backing-up to a hitch.

You won't easily find a rheostat in that Ohms or Power, and a rotary device doesn't really suit the inching-pedal it has.

I say polish it up and call it done for the next 60 years.

Just FTHOI, have you asked Clark? (Looks like you have to work through a dealer.)

[shooter]

have you asked Clark

The owner, also the owner to our neighborhood grainery, tried, he still has one guy a 100miles away trying, it's just *so old* is the Clark reply.   I found a couple rheostats in the 0-10 ohm range, but nothing bigger than 500W unless I go PWM.  The problem there, will the motor *stutter*? think flickering lights on a PWM dimmer
I hope he does get 60yrs outta it, He asked how much I charged, I told him a tour of the grainery

[Willabe]

I hope he does get 60yrs outta it, He asked how much I charged, I told him a tour of the grainery

       

[PRR]

What's wrong with it as-is?

No wimpy PWM gizmo will give longer service.

[shooter]

The biggest problem is the "copper" facing on all the carbon pucks is heavily pitted, also eroding.  I'm just afraid they will, crack, or arc over.   

[PRR]

They won't arc much on 12V. In fact the way that resistor is rigged, they "CAN'T" arc, because even if the motor kicks-back 100V, there can't be more than a couple volts across each disk.

Yes, they will continue to corrode. Emery-cloth best you can and suggest getting a less-old forklift before another 60 years goes by.

The cracked disk can be bonded with epoxy or JB Weld. When cured, file and sand the glue flush or even below the carbon/copper conducting surface. But if it will stay by bolt-pressure, or if it "works" with 6 steps instead of 7, I'd go that way.

If the Boss wants faster production with less inching-damage to skids, let him buy a better machine. I assume this is a "useful toy", like my young (1967) backhoe, and not a big-profit operation. My hoe will lift 700 pounds of muck, but when I rev it up to lift 1,000 pounds I blow hoses. It actually creeps fine; doesn't really want to climb hills like it obviously did when younger. If I had the contract to re-drain the Rt1-Rt3 intersection I'd want everything on the hoe in great shape. If I'm making holes in the yard for no pressing reason, I just let the hoe do what it can. 

[PRR]

> cabled up with #8 copper. ... I don’t have ... I.

Under NEC, #8 is allowed 40A-55A depending on insulation.

Wires are short, nothing to burn, loads are mostly short-term, so I assume they may take them past this point. Fusing Current for #8 is estimated as ~~472A for 10 seconds, >2,000A for 1 second. The insulation will burn long before.

(Note that fuzzy grey/white insulation is The Magic Mineral, asbestos. There is bad and worse asebstos, and you don't know which mine it is from. Don't futz with it. Be good to spritz with soapy water before going in. Wash after.)

Taking a split-difference from 40A to 400+A gives around 120A.

BUT there may be sub-Second peaks to much higher currents. Not long enough to heat big copper or carbon, but more than long enough to melt Silicon PWM systems.

Are you sure about the 12 Volts?? 12V at 120A is only 2 Horsepower peak, and only 1HP for the longer haul. A 2013 Toyota e-lift has 14HP motor. Probably a heftier machine because all cargo handling has got more frenetic. The new Toyo (like older forklifts I have run) uses a 36V or 48V battery. (Higher voltage so the copper sizes don't get awkward.) 36V/48V at 100A gives 5HP/7HP which seems more useful. (Remember that strong men can burst over 1/4HP, so a crew can do the work of a 1HP/2HP motor, and you can lay them off at whim whereas the truck payments were ongoing.)

Yes, all of this is well in the range of Electric Car (even heavy Golf Cart) controllers, which are now totally electronic. But the cost of a new or known-good used controller must approach the true value of a 1954 Clark.

[PRR]

Link is the Army manual for a 1963 Clark e-lift. Tool-gear icon top right you can download a 3MB PDF. It does show two 5HP motors. I do not see the inching resistor you have. There is a schematic in the back but the idiots at Google Books didn't open the fold-out when scanning.

There is an R&R-time for "carbon pile", but I don't see a picture or process.

[PRR]

Are you very sure of the 7.4 Ohms for the total stack of seven? That seems to give a huge jump from the last (1 Ohm) step to full-out. Like from 0.5HP to 5HP.

The carbon disks are just resistors. I dunno where to find such stuff today. It isn't "pure carbon" but has been doped for strength and some specific resistance for its size. (Carbon brushes are doped with copper powder to reduce resistance, but here we need a specific resistance in a specific size.)

In principle you can replace them with thin copper and insulating board for shape/size, and external resistors.

The power capacity of a carbon pile is HUGE compared to any standard resistor, so this will be bulky.

It will be hard to find any resistor with #8 leads (though studs can be found).

If not held hot for long periods, Iron Wire is a fine resistor at trivial cost.

The Fusing current obviously does not have to be higher than #8 copper.

http://www.powerstream.com/wire-fusing-currents.htm

Hmmmm, this basically says 1/4" iron rod. As your disks seem to be near 1/4" thick, it won't add-up.

Four strands of #9 iron wire has similar capacity to one #8 copper. Interesting because #9 fence-wire is about as cheap as wire gets; may be a roll in the shed.

Now the question is: what resistance? As I say, 7 Ohms seems unlikely. You may have a bad contact in there. However it makes math easy, 1+ Ohm each.

Since we need four #9 strands parallel, each strand must be 4+ Ohms. Ah, problem. #9 copper is 1073 feet per Ohm. Iron resistance varies a lot but say 7X copper. That's 150 feet per strand, four strands per step, 7 steps total, is just shy of a mile of #9 iron wire. I don't see any way to wrap that into a Clark so it gets air but doesn't short itself. NiChrome would be shorter, but not that much (the real advantage is that it will run red hot for years), and much more expensive.

Another technology: liquid rheostat.

[shooter]

If I can get outta bed by 7am I'll be having coffee with the 'ol guys and hope to get my clamp-on for a current reading and a better understanding of how this rheostat fits into the system.
On the bench each puck ohmed about 3.4, with 2 in ||, for an overall 1ish ohm per stack, 7 stacks, I ohmed 7.4 with all contacts open, 1.1ish with all contacts closed.
This is the last Mom n Pop grainery left in the area, and they are probably the last generation. 
He does have a modern '70s era clark
The original setup was 6V, but somewhere along the line it got switched to 12v.
Thanks for the link, thanks for the interest.
This *fix* got around, so now it's a broke tone arm on a record player
As I'm now the *interesting guy* that sells beer bait and cigarettes at the last American owned, middle of nowhere gas station, I think i'll be blest with many interesting *projects*
Thanks again PRR

[shooter]

well I made it, 17deg and fog-ice, in a steel building!
my clamp-on amp meter doesn't have a peak-hold feature, so not very accurate readings;
low end readings, about an amp, high end 12 - 16amps.  It's not totally *fixed*, there is still a jerk, but it is much smoother than just bolting the wires together.
If I double the 16 to 40A *12V, I'm at 480W peak?
Ohmlite does make rheostats in the 10ohm 500W but they are pricey.
The owner has completely re-built the motor and hydraulics, and he's satisfied so it's on to the broke vinyl player!