New user with Cosmo 170 (SIP) and a headache

Try a zener diode in parallel with the motor. You will have to experiment with different voltages, use 5 watt types minimum.
Have used these before with success, on small migs.

Back to welding with a less than perfect welder

Background April 2009 Marham track day resulted in a nice crack in the screen

Managed to get the Monza thro an MOT in sept (with an advisory) helped by the fact a new screen was 2 months wait and the crack was just outside the swept area

So this weekend old screen came out as I figured I might have a bit of work to do (water leaks give the game away)



So all the grey bits show where any minor surface rust was ground away and treated before a coat of zinc anti rust primer

However some bits need some sparks pointed in the general direction



Theres me water leak then

Nasty but solid



Another bit scabby



And not so bad but hey ho once I've got the sparks out it'll look a lot worse



Anyway it's a track car so it doesn't need to look pretty and I need to get the bloody thing out of the garage and round into a friends garage so I can finish the LC

All done now - Content warning CONTAINS SHOCKING EXAMPLES OF MY POOR WELDING SKILLS

So moving on

Was a hole Hit it with grinder then dented the metal and filled it with weld ground it back - worked a treat - yes I know it's not the best way but "it's a track car" and one day I'll put it on it's roof so I'm never that fussy



Zinc Primer Applied



This was the one I was worried about - but I made up an insert of 20 guage steel - stitched it in and it looked OK - Well apart from the crappy welding :lol:



Ground all the excess weld back (sorry for poor pics I was on a mission)



Zinc Primer



Same Trick from earlier repeated on the passenger side corner - just a finished pic



Then got the top coat out (hammerite silver and black self mixed at Le Mans Classic 4 years ago to match the body colour when I had a day to kill and a primered roll cage to paint) was a good match then and not too bad now and as I had some spare seemed a shame to waste it :lol:









See a blind man on a galloping horse wouldn't notice the difference :roll:



Ready to get the new screen fitted now

Meantime I have to say it was a pleasure working in the garage tonight - temperature outside was 3 deg C - with no heating needed - previous to the garage improvement project temp in the garage would normally have been same as outside - frapping cold and even with heating frostbite was still a high probability if the temp dropped below zero!!

However over the summer I've been preparing the garage for the winter projects in last 4 months I've been

- Plasterboarding the roof of the garage
- Redoing the lighting with 6 new striplights
- Insulating above it - 3 - 4 Inches of insulation above the plasterboard
- Boarding it out above that to provide storage in the loft for all my spare parts
- Adding a loft hatch big enought to get panels and bumpers thro it
- Painting walls to cut down on dust
- painting the floor

Still got a couple of things to do but they are nice to do rather than essential power socket ring main round the garage and hard piping for the compressed air system

Doesn't look like much for the effort put in but without any heating the garage was a nice comfortable 14 Deg C tonight when I left it having finished the Monza

Well new screen is in

Fitter was chuffed to find a car with the screen already removed, the rubber seal and the trims all cleaned and ready to fit

I explained to the autoglass technician I didn't want any sealant I had to sign a disclaimer to the effect that if the screen leaked they wouldn't be liable. There were a couple of reasons for this but the main one was the rubber trims aren't avaliable any more and I think that if they use the sealant it will stick it to the shell making it more likely that if the screen is removed again the rubber seal could get damaged

But the screen went in perfectly first time - pulled nicely down all round and the trims fit really well (this is great as for the last 4 years I haven't had the trim on one side as when the previous screen was fitted the trim was not avaliable (it got runover by a lorry) Replacement Trim above I got from Matt Alcock a few years back

So screen in



While the screen was out I took the opportunity to do a little bit of cosmetic work - especially as I found my long lost Ray Ban wafarers sitting in one of the holes (I had really missed those sunnies, they were a gift from my sister over 20 years ago and the best driving glasses I have ever had) I was so chuffed to find them I nearly stuck Don Henly Album in the tunes box and went for a drive 8) (it was raining!!!)





Then I remembered something was missing (the rain was a clue)



While the screen had been out I took the opportunity to replace the wiper motor and linkage assembly as the old one parks as well as Lisa (my OH), That was a job and a half as it appears I have a roll cage the seriously gets in the way of the removal process - once out however I was able to set the new one up to give the max clearance and it went in slightly easier.

Guess how much better the replacement was at parking??? - answers on a postcard

PS so that's all for now on the Monza - need to roll it round to a friends house and park it up till the new year as the big green thing is next and lots to do to that - bloody vauxhalls are bad enough but when lotus get involved it just gets worse

A couple of questions to BChild and anyone else that can answer-

1- has anyone that have done the wire feed power supply mod feel the multi-turn pot for speed control would be of benefit or are you able to control the slow speed adequately with the original pot ?

2- I mainly need the MIG for car repairs and the ocassional light welding - if I need to do anything heavy I have a stick welder for that. After the power supply mod my original speed knob is driving approx 6m/min at half way round the dial so if I could spread that out to nearly full turn I'm hoping I would get a better spread at the slower speeds - any ideas on doing that - will the trim pot on the board provide that or just delay the start and compress the range?

Originally Posted by Wombat 1- has anyone that have done the wire feed power supply mod feel the multi-turn pot for speed control would be of benefit or are you able to control the slow speed adequately with the original pot ?

I'm able to control the speed fine with the original pot - mine can now weld nicely over a fair range of the pot travel for any given job and isn't "fussy" at all so I don't feel the need for any finer adjustment.

Originally Posted by Wombat 2- I mainly need the MIG for car repairs and the ocassional light welding - if I need to do anything heavy I have a stick welder for that. After the power supply mod my original speed knob is driving approx 6m/min at half way round the dial so if I could spread that out to nearly full turn I'm hoping I would get a better spread at the slower speeds - any ideas on doing that - will the trim pot on the board provide that or just delay the start and compress the range?

I think the trim pot will just compress the range. It sounds as though the voltage from your new power supply might be a bit on the high side for what you want. That will determine the wire speed at "full throttle".

Originally Posted by BChild tonight I had my nephew in the garage working on his mini and he said you can hear the motor getting faster as you weld.

Originally Posted by shenion The design of the SIP circuit is poor. It will change as the transistor heats up.

Originally Posted by BillJ Mine doesn't do this and in this circuit I don't believe the voltage drop across the transistor would be affected significantly by the temperature of the transistor.

Having said that, after welding outdoors in recent cold weather, I have started to notice this effect too

As Shenion mentions, this will be down to voltage regulation varying with temperature. The transistor in this circuit is a TIP35C, which has a hfe that could be as low as 25 in this application.

The original circuit will have been designed that way (a variable voltage-drop) because of the intention to use the different welding voltages to provide automatic speed ranges. With a fixed-voltage power supply for the wire-feed, this is no longer necessary and a more stable variable voltage regulator would be more useful (I think R Kraft mentioned this earlier).

I'll have a look around to see what bits I have to knock something up. The simplest route would be something like an LM317 variable regulator (if I have one) which would need only a handful of extra components. I could wire my bench power supply in there but I think that's an expensive option

Normally the wire feed is fed from the welding voltage, which would be from approximately 15 to 20 volts.
I don't recall now how many volts the separate transformer supply puts out.
It seems that to get the low speed with the higher voltage, the transistor is being biased into a very temperature sensitive spot.
An LM317 should work, or the stepped regulator I put in my album:http://www.mig-welding.co.uk/forum/a...pictureid=3062
Robert

Originally Posted by Wombat A couple of questions to BChild and anyone else that can answer- 1- has anyone that have done the wire feed power supply mod feel the multi-turn pot for speed control would be of benefit or are you able to control the slow speed adequately with the original pot ?

My situation may be specific to my SIP but I couldn't control the wire feed speed with a single (act 3/4) turn pot

Several reasons

1, it was non linear at the start and end of it's range

2. I was running the welder on low settings so was on the cusp of the non linear area of the pot

3. The wire feed speeds up as you are welding

Had I been working with 2-5mm steel the problem wouldn't have been so obcious or difficult to manage

Originally Posted by Wombat 2- I mainly need the MIG for car repairs and the ocassional light welding - if I need to do anything heavy I have a stick welder for that. After the power supply mod my original speed knob is driving approx 6m/min at half way round the dial so if I could spread that out to nearly full turn I'm hoping I would get a better spread at the slower speeds - any ideas on doing that - will the trim pot on the board provide that or just delay the start and compress the range?

I'd recommend the 10 turn (or maybe even a five turn) as it has enabled me to fine tune the wire feed speeds - something I found very difficult with the single turn (act 3/4) pot

just adding to this, almost gone to the wall thread.

I've just completed adding a separate transformer to my Cosmo gasless 100. i know, i know its only gasless, but it was a pressie. and I do all my welding outside. do that with gas. any time of the year ( well rain excepted )

a long time back I did the brace to the drive rollers, a good mod. also I noticed twisting movement on the movable arm of the driver rollers, on the inside ( mounting closest to the drive gearbox ) a thin metal washer here stops the arm twisting on the shaft.

as my low end gasless 100 doesnt have a control board, only high and low amps ( 90 and 25 ) and the motor speed had no control. I decided to add a PWM controller ( made my own circuit, but any of them able to handle 24 volts will be fine. I put my scope over the motor and in my case the power supply is terrible as many have already found out. the pre-switch voltage will supply 11 volts at low speed and 16 at high )

so I set a 3/4 turn 47K pot. to be offset in its voltage output to vary from 8 volts upto 20 volts ( i did this by adding a 33k resistor to the low end of the pots resistive track. and to feed the supply the wire drive motor from my separate transformer.

I can adjust wire speed from approx 10inch per minute upto nearly 300inch/min now. using a proper PWM circuit and a MOSFET instead of a power transistor will be much more stable over its temparature range. the standard cosmo/sip motor draws approx 400 milliamps free running at 100% duty cycle on 20 volts supply.

I too also put a relay brake on the motor control circuit, and I added a flyback diode across the motor itself.

after already hearing about the temp variations. i've run over 15 minutes of running at high power ( hehe, only 90 amps ) but its got such a low usage cycle at this setting everything inside was getting warm I experience no wire feed variations at all.

I've been able to use the low setting to do welding now... in the past the motor control was so poor it was unusable. now i can sizzle my bacon at either setting, and get excellent penatration... even on 3mm steel. which i've never been able to do before. this welder had struggled welding 2mm before.

to everyone thinking about this... do it properly fit a PWM controller, and a transformer... use the normal control circuitry to supply your brake switching relay. doing it this way you'll not suffer any variations on motor speed, you'll have precise control from the pot controlling the PWM circuit and thus wire speed. welding will become so much more relaible.