electric forklift speed control

I'm one step ahead of Gunner. I'm calling my work on the new 30 year old gas forklift complete. At least until it breaks down.
Now I'm back to my old reliable Big Joe electric. It has a frustrating problem that's getting worse. When there's a heavy load on it, the truck won't move when in 1rst gear. Then when it hits second gear it jumps like my kid peeling out from a stop light with his 500 hp Mustang. Makes it very hard to set one bin of fruit exactly on top of another.
The speeds are done by bringing in three solenoids (1,2,3 gear) to different taps on a power resistor. The drive motor sees a higher voltage for a higher gear. It looks like it may be possible to unbolt the taps and move them on the power resistor. Anyone tried something like this?
That power resistor gets HOT. Lots of wasted energy. That got me to thinking, do newer forklifts use some kind of power transistor speed control that could be retrofitted to this unit?
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Karl Townsend wrote:

I'd measure the voltage drop across the first solenoid contacts. I'll bet that the first one is burned or corroded. You might try swapping the high and low solenoids and see if the symptom moves.

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I'll try checking this. but, I put in all new silver contacts and motor brushes last year. They didn't look like they could even use a filing this year.
Karl
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Years ago I worked for a company with a large warehouse. The one fellow drove a three wheel cart when he went to pull small orders from the shelve. The cart had a similar control to yours. One day the warehouse forman drops a box on my desk and tells me to install "it" on the cart. Turned out to be a Dart motor speed control. The install went pretty easy considering I had no experience with the cart, or the control. If you really want to go that route I would contact Dart and see what they can do for you. My guess is the cost may be prohibitive. Greg
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...

I'm sure you're right if I buy a commercial retrofit. Is this what you installed? www.dartcontrols.com/InternetConfig/Catalog/65ESeries.pdf
I'm sure I'd need their 60 amp (biggest) unit.
If it has been done (sounds like it has) I bet one can be designed and built. Anyone know of a reasonable expense route to go?
Karl
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It was a few years ago so I can not recall any details, but it was manufactured by Dart. Greg
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On Fri, 01 Sep 2006 23:26:52 +0000, Karl Townsend wrote:

Product Catalog http://www.curtisinst.com/index.cfm?fuseaction Νatasheets.dspListDS&CatID
You will need, one of these. http://www.curtisinst.com/index.cfm?fuseaction=cProducts.dspProductCategory&catID 
Two of these, one forward, one reverse. The directional solenoids you currently have may work. Then you wouldn't need these. http://www.curtisinst.com/index.cfm?fuseaction=cProducts.dspDcContactors
One of these. Your directional control has step switches. Newer units use speed pots or Halls effect sensors for speed control. http://www.curtisinst.com/index.cfm?fuseaction=cProducts.dspProductCategory&catID %
Associated and auxilary cables, wiring and related mounting hardware that will have to be custom fabricated. Patience, tools and time.
If it was *mine*, I would reset tap points on speed resistor first. Being careful! Higher first point of power will cause unit to move quickly (jump) with no load. I would be sure the belly button switch works properly before any modifications are made so it couldn't pin me against a wall or trap me. Then I would *load* the unit and try transitional speed change to second speed with a secure load in lowered position to see if the change is a smoother operation.
My recommendation for you is hire a professional that has done these modifications before and do what you do best in order to pay them.
Modifying equipment today can make you the manufacturer in court when someone gets hurt. There are more great attorneys today than great mechanics. Both have learned where the risk lies.
CYA, and good luck.
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Check the 1st gear tap on the resistor. The point of contact may be corroded. Bob
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Karl Townsend writes:

Yes, DC motor speed controls are typically PWM MOSFET circuits. Much more efficient.
Automotive blowers still use resistors.
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On Fri, 01 Sep 2006 21:16:58 GMT, "Karl Townsend"

Have you checked the output to verify that you don't have an open cell or possibly a bad battery if it's run on multiple batteries in series? Has it run ok before and just started acting up or has it always been jumpy? If its always been jumpy then you will have to move the leads on the resistor to give you more power in first speed mode. If it just started acting up you will want to check the connections at the resistor/resistors.
There are many ways to convert this truck to an electronic control but they also work fine if they are set up properly as well.
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On Fri, 01 Sep 2006 21:16:58 GMT, "Karl Townsend"

I wonder if the taps vary field current rather than armature current. Max field current would be lowest speed and highest torque for given armature current.
If it's varying field current, I don't think it'd be a big deal to make a MOSFET control for it, not greatly different from the boatlift motor gadget I recently made. We'd need to know if it is really field current control, and if so how much field current.
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I just pulled the electrical prints. Yes, the armature sees the same constant 12 volts at all times. The field either a) bypasses the power resistor, b) sees 1/3 of the resistor, c)sees 2/3 of the power resistor
Karl
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On Sat, 02 Sep 2006 10:21:57 GMT, "Karl Townsend"

Maybe I'm reading the print wrong, but it looks to me like the armature is always in series with the field. I don't see a path from +12 thru the armature to gnd except via F-2 thru the field winding.

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This is probably just plain stupid for a mechanical engineer to disagree with an electrical engineer about electrical prints. There are four brushes on the armature. The print shows A1 and A2 at battery voltage when the proper contacts close. I think the other two are connected to the motor frame. The print also shows F2 at battery voltage when the proper contacts close. My conclusion is armature always sees full battery voltage and the ground route is not drawn in. Field sees voltage from full battery to current power resistor connection (F1).
Karl
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On Sat, 02 Sep 2006 21:08:03 GMT, "Karl Townsend"

Hey Karl,
<
http://www.metalworking.com/dropbox/forklift.JPG
This schematic definitely shows that the Field is in series with the Armature at all times a direction is selected. (Best way for it to be too.) Forward and Reverse are selected by changing direction of current flow ONLY through the Armature (Field is always the same polarity)
The low speed section of the"Speed Control Resistor" is ONLY in the circuit while in low speed. It is shunted when the relay marked "2ND" pulls in.
The other section of the"Speed Control Resistor" is ONLY in the circuit while in "2ND". It is shunted when the relay marked "3RD" pulls in.
There is none of the"Speed Control Resistor" in the circuit while in "3RD". The motor is hooked direct across the battery for this highest speed.
The only thing that can effect "only" low speed, as you describe in your original post, is the portion of the "Speed Control Resistor" that is used when it is in low speed, AND THE WIRES AND CONNECTIONS TO THAT SECTION. (Note: It is not possible to tell from this schematic if there is only a single resistor grid with multiple taps, or two separate resistors)
It would seem most likely that you have had a connection loosen, and it is arcing and causing further resistance, or even an open, and hence the on-going degradation. If I get a guess here, the wire from "F-1" would run from the motor direct to a upper contact on the "2ND" relay, and a separate wire from that same point to the resistor; and then the wire from that first tap on the resistor would run direct to the lowest contact on the "3RD" relay. Check any one of those connection points for tightness. Be careful not to burn your fingers if you have just run the machine.
Take care. Good Luck.
Brian Lawson, Bothwell, Ontario.
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On Fri, 01 Sep 2006 21:16:58 GMT, "Karl Townsend"

Need another Big Joe? Ive got one taking up space in the driveway. 2000lb capacity. Some dickhead pulled the brush assembly out of the traction motor and lost the parts. I need to find a parts list to order the brush holders, brushes and insulators that extend out of the motor case. They claimed it ran, but the brushes wore out..the low man on the maint totem pole tore it down and then lost the parts while waiting for new brushes.
Its the one with the outriggers. Id let you have it cheap. Really cheap. goes up and down nicely. Just doesnt move without those brush parts. I slid it under the pickup and lifted the front end to change brakes last month.
Gunner
"I think this is because of your belief in biological Marxism. As a genetic communist you feel that noticing behavioural patterns relating to race would cause a conflict with your belief in biological Marxism." Big Pete, famous Usenet Racist
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DAMMIT Gunner, Why don't you live about 2000 miles closer to me? Then most of your junk could be my junk. Instead of just having too much stuff to fix, I could have way too much stuff to fix.
Parts are still available, but hold on to your shorts for prices. Last year, I bought two sets of brushes and five pairs of solenoid contacts for only $600. I'm pricing a new battery for this year, bet its over one kilo-buck.
Karl
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On Sat, 02 Sep 2006 09:15:37 +0000, Gunner wrote:

Get the numbers off the motor and contact these folks for the parts your missing. If he doesn't have the parts in stock, he'll get them. Prices were always reasonablely priced, as industrial truck parks go. Material handling manufacturers and dealers were always proud of their parts and are priced to let you know just how proud they are of them. ;-) http://www.genesiselectricmotors.com/index.htm
Doesnt look like there are that many possibilities for Big Joe drive motors. http://www.genesiselectricmotors.com/cgi-bin/gemsearch/free-search.cgi
I retired, but have used this vendor, but am no way affiliated, except as a former customer. HTH

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On Sat, 02 Sep 2006 11:25:25 +0000, RLM wrote:

Sorry link didn't work. I went here and entered " Big Joe&&drive motor " less quotes. http://www.genesiselectricmotors.com/gemsearch/free-search.html

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see
http://www.metalworking.com/dropbox/forklift.JPG for print.
I took some voltage measurements.
Node: No Pump 1rst 2nd 3rd Load on gear gear gear A 11.7 9.7 10.0 9.8 8.8 B 6.6 4.4 0.2 C 0.2 4* 0.2
Node A is battery plus terminal Node B is top of resistor or motor F1 Node C is bottom of resistor
Voltage measurement is when first engaged. The number climbs as lift comes up to speed.
* This voltage was all over, 1 to 5 volts.
mean anything, other than I really do need a new battery?
<(©Ώ©)> An apple a day keeps the doctor away. Two apples a day gets the doctor's OK. Five a day makes you a fruit grower like me.
Karl Townsend
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