Thread: Help needed ..Electrical

I'd try to get some info from the buggy manufacturer. With a bit of smooth talking they may well lead you directly to a supplier or at least give you info on the manufacturer.

Most pots have their value and whether they are linear or logarithmic stamped on the back. Otherwise you can use a multimeter to measure the resistance and its characteristics. The other info that may be important is the power rating but it sounds like (from the size) that this is not a worry for you.
Another alternative is to replace the speed control all together. Oatley Electronics have a good range of cheap DC speed controls, some seem to come of golf buggys.
Sterob

The 'marlin electric vehicle manufacturers' of Beenleigh, seem to have gone out of business since 2004. can find no info on unit.

Thanks for suggestions Sterob..have emailed Oately Electronics, to see if they can help.

The pot will be the actual control element that the driver handles, but the actual speed control will be moderately complex electronics buried away out of the weather.

The actual pot will most likely function as a variable voltage divider, i.e. a regulated voltage like 5V or 12V will be applied accross the pot end terminals and a voltage proportional to the position will be output from the centre terminal. The actual speed control will then adjust the effective voltage applied to the motor in proportion to that signal. The motor system is probably at least 400W, while the pot is probably .25W or .5W, and most definitely under 3 W.

You haven't been overly specific about what sort of problem you are experiencing, but as an electronics eng with experience in elec wheelchairs and scooters, I suspect that the problem is actually in the speed control module or the wiring harness, rather than the actual pot. If you supply some more info I can try and help by remote betwwen now and Christmas (pretty busy till then then) or more directly afterwards.

Thanks for kind offer malb.
The Scooter has two drive controls
(1) Speed limiter marked "snail" to 'Full'
(2) Main control Forward or Back for direction, with pressure increasing speed

The Electronics are provide by a 110A RHIN " scooter control" made in NZ

Problem appears to be intermittent contact in the Alpha 3B potentiometer of speed limiter. If on sweet spot runs OK , or cuts out and another contact point has to be found by rotating knob.

Was considering a temp: bridge across the two soldered terminals on this control.. would this give full speed .. or should i include a resistance and fuse?

I could then check to see if other control was OK

Originally Posted by Paddy

Thanks for kind offer malb.
The Scooter has two drive controls
(1) Speed limiter marked "snail" to 'Full'
(2) Main control Forward or Back for direction, with pressure increasing speed

The Electronics are provide by a 110A RHIN " scooter control" made in NZ

So far this is as expected, I have seen this arangement, and an alternative where the pot is part of the control 'lever', and acceleration, deceleration, and top speed are variables that can be programmed into the controller.

Problem appears to be intermittent contact in the Alpha 3B potentiometer of speed limiter. If on sweet spot runs OK , or cuts out and another contact point has to be found by rotating knob.

Sounds like the pot may well be the issue then, It has either worn through the carbon resistance track, worn the brass wiper, or accumulated a dose of dirt and dust internally. Alps used to be at the top end of the consumer use pot models, better than many but not as good as the specialist units used in some Pro gear like $50,000 recording studio mixing desks. Some of those pots could be $200+ each.

Was considering a temp: bridge across the two soldered terminals on this control.. would this give full speed .. or should i include a resistance and fuse?

Are there only 2 terminals on the pot, would normally be three, but may be connected as two wire system (variable resistance mode rather than variable voltage 3 wire system)? If connected for variable resistance (2 terminal), a third terminal may have been cut back during system assembly.
Pots normaly have the nominal value stamped onto the case rim opposite the terminals. This normally takes the form of 1, 2, or 3 digits followed by R or K (e.g. 1K, 100R, 10K etc).
If the unit is configured as a two wire system, bridging the terminals with wire would be unwise, but using a resistance of similar value to the pot nominal value should be safe. Should not need a fuse as the current would be less than 5mA .
If the pot has a shaft and knob, then it is normally possible to take the cover of the back and clean the resistance track and wiper with a pencil eraser, but outright replacement is often a quicker alternative if a suitable replacement can be found.


I could then check to see if other control was OK
Yes, this would also check the rest of the system for intermittents etc as well.

Mal

Thanks Mal.......attach a couple of pics, B20K marked on the back of terminal board, with the first two terminals used, last one unconnected

Paddy, I have done a bit of hunting through my usual haunts but can't come up with an exact match. Seems that pots in stores these days seem to go in a 1, 5, 10, type sequence and leave out the 2 (or 2.5) that used to be fairly common.

In 16mm pots (as original) Dick Smith (Chirnside Park) and Jaycar (Ringwood) should be able to supply 10K or 50K units for around $2.

In 24mm pots (if you have space to mount it in the housing) Jaycar list a 25K linear unit (B curve) . I suspect that this is probably the best match you will get, provided that you have mounting space. It uses a 3/8 mounting hole and 1/4 inch spindle so you might also need a new knob to suit. It has a full length spindle, but this can be cut down to suit. Their catalogue number is RP3514, website is www.jaycar.com.au.

If the unit was configured as a voltage divider (three wire) you could probably get away with a 10K unit, but in variable resistor mode (two wire), 10K would not give the slower speeds, and the speed range would be probably 20% to 100% of original max.

Alternatively, using a 10K pot with a 10K fixed resistor in series would probably get you dead slow to 30% of original maximum speed.

I would suggest that you phone to check availability before travelling to buy a part as both shops are prone to stock shortages from time to time.

Mal

Thanks for all your advice Mal, much appreciated.
Without thinking hit the download button for the latest Jaycar catalogue last week and left the room for a while.. It was 400 MB!! so i will follow up with them.
Hope your back on your feet...

Foot and leg not great, but now able to spend maybe an hour on it at a time without serious grief. Boss still trying to encourage me back to work, so I have promised him Saturday morning delivery run, 5-6 hours, 30% driving, balance on foot. Will be running stockings and antibiotics to keep it tamed, plus I have Sat pm and Sunday for it to settle. If it can cope, I will go back full time on Monday.

Had been hunting a job since Feb, got this one two months ago, then get grounded for a week in the crazy season (Parcel Post deliveries). Still, the boss has been very good about it to date, but I don't want to push my luck, can't affford to either.

Hope you can make some progress with the buggy soon so that SHMBO can have some mobility. I do have a dual 20K in 24mm if you strike out on availability, you could have that for nix and just wire up one section of it, but it is about 3/4 inch deep so space might be an issue. PM or email if that will help and I will fish it out for you and send a pickup address to you (2min from Maroondah Highway/Dorset Rd intersection)

Mal

Paddy
Have you replaced your potentiometer yet? If Jaycar don't have any try Farnell or radio Spares - don't bother with Dick Smith, Woolworths are gradually turning them into a convenience store

Either:
a) Get the 25k, 16mm linear taper from DSE or Jaycar and wire it like a rheostat - ie. center terminal and one outside, depending if you want resistance to increase with clockwise or anticlockwise movement. The 5k extra resistance will simply mean that at the low end, it goes even slower or stops, but it won't affect your maximum speed like adding a series resistor will. This will be $2-$3

b) Order from Farnell. Here is the link. They have 4 in stock in Australia as I type this. Be prepared to pay $10 delivery fee for something that costs about $1 to post though. Still, you will get the right thing, and you will get it in about 2 or 3 days. I'm fairly impressed with this company. Make sure you also buy from them a knob that fits and is a style you like.

c) Order from Futurlec. Prices are great, but you may wait weeks or months to receive this as it comes from Thailand. You need the 1/2W Linear Taper POT20K from here. Just make sure if you go this route that it isn't an emergency, or you (or your wife) will have rotted in the ground before you receive what you need. However, for bulk electronic components that are hard to find or 4 times more expensive anywhere else, I think Futurlec is great.

Dont know if they are still there but try Truscotts Electronics in croydon. They used to carry a good range of pots.

Roger