hot rods

[martinez]

welded a few brackets up for a mate recently with my Murex 150 inverter, noticed that the rods were glowing red hot by the time I was half way through one, is this a sign of too much power ? it was difficult to assess the correct powere as i was at the end of a 45mt extension lead ! so had to turn it way past the 80 amps I had used with 2.5 rods.
any advice, apert from use a shorter lead ?

 

[madkayaker]

its quite normal for some special rods you use the first bit then let the rod cool while you use another and keep going like that or the flux falls off

 

[Welderpaul]

If your rod is glowing, you have too many amps for the size of the rod.

 

[TechnicAl]

Rods shouldnt overheat

Like Paul says its too much current or if its on the wrong pole, some rods will overheat DC- but they are fine DC+.
I think long leads can reduce the voltage so the effect is similar to putting the amps up (but I could be talking b******s)

 

[PTvor]

Inverters have a reputation for acting up with long mains leads, and upping the current may not be the answer.

any advice, apert from use a shorter lead ?

Use a buzz box if you have one around.

 

[decepticon]

doubt that if the extension leads are of a decentish size that 45mtr would cause any difference if you kept to 80-90 amps (more than enough for a 2.5). it travels further than that through house wiring anyway!
why would a 'buzz box' be any better, i thought inverters were the most efficient machines?

 

[Welderpaul]

Any more than 3x 2.5mm 110V extensions on our inverters and you notice the power drop.

 

[PTvor]

doubt that if the extension leads are of a decentish size that 45mtr would cause any difference if you kept to 80-90 amps (more than enough for a 2.5). it travels further than that through house wiring anyway!
why would a 'buzz box' be any better, i thought inverters were the most efficient machines?

The bookie which came with my inverter has a table of output current/extension lead length and lead cross section saying that up to 25 metres, 2.5mm flex is fine but at 50 metres you need 4mm flex. That's with 90-100 amps output. It doesn't explain what you need at distances between 25 and 50 metres. It says, "this is to reduce voltage drops and reduce risk of damaging the inverter welder".

Most decent quality extension cables are 2.5mm, people just don't need the extra expense and clumsiness of 4mm extension leads to run lights, power tools etc even at 50m. Welders are a bit different in the load they impose.

Buzz boxes are just transformers but inverters are a lot of complicated electronics liable to get confused if things aren't right.

I suppose another solution, apart from using a 4mm extension lead, is to do a codge using two 2.5mm extensions in parallel.

However, if martinez' 45m extension lead isn't 2.5mm anyway, and some of the extension leads I've seen are not, that may be the answer.

 

[brightspark]

2.5mm is the largest cable u can get in to a 13amp plug so no chance of doubling up

 

[PTvor]

13 amp plug for a 150A inverter? Shame on you.

The bookie I have also goes on to say that since the inverter welder requires a 16A fuse it is not classed as a domestic item and therefore comes without fitted plug and a suitable 16A plug should be fitted. Leaving things down to the buyer. I doubt the Murex 150 is different.

Anyway, I did say codge.

 

[brightspark]

i made no refrence to the welder amperage just the size lead that can be fitted in to a 13 amp plug .also i wouldnt run any welder or heavy load of an extension lead no matter what the length

 

[keith19]

i made no refrence to the welder amperage just the size lead that can be fitted in to a 13 amp plug .also i wouldnt run any welder or heavy load of an extension lead no matter what the length

What? You've never worked on site?

 

[Sean]

The bookie I have also goes on to say that since the inverter welder requires a 16A fuse it is not classed as a domestic item

Whats the odds on you melting the 13a plug?

 

[PTvor]

Whats the odds on you melting the 13a plug?

With a 130A inverter and a quality plug (with 13A fuse, not a paperclip) not great, but the with the inverter set to 130A the plug and socket will be near or beyond their limits, so it isn't ideal. It doesn't blow fuses at 130A.

Getting back on topic, I think what's happening with an inverter on a long lead with significant voltage drop under load is this.

The inverter has a set of big capacitors which it charges with rectified mains, to about 340V. In normal use with a short lead, they can be kept topped up to say, over 300V even with the inverter delivering max amps. The electronics convert the over 300V DC into 20 odd volts at welding current, and there's a feedback loop to keep the current to a set value. It all assumes the voltage on the capacitors doesn't drop below a certain level, maybe 290V under any conditions.

If you have a very long lead with voltage drop, the capacitors can't be topped up, as required by the design, when the inverter is delivering welding current and the current setting mechanism can't work as designed.

However, under no load the capacitors will charge as normal so if you want 80A and set the current to 110A to compensate for the cable, the inverter will deliver 110A for a time after you strike the rod, until the capacitors discharge, and 110A is much too much for a 2.5 rod.

It isn't a safe assumption that setting the current to 110A to compensate for low voltage will cause the inverter to settle down to deliver a steady lower current either.