Resistance-No Resistance wire welder

[yo han]

Thanks but all I did was adding some of my own ideas and visualizing it.
I couldn't have done it without awsum140's help.
Not everyone will want to use the same terminals for welding and measuring, it's just my personal preference and can easily be changed.
If anyone's got comments or improvements for the last schematic I've posted then please post it here.
Also, I have zero experience drawing schematics so if I've made mistakes then please let me know.

 

[tobarger]

For someone with zero experience your doing amazingly well
I have years of experience and couldn't do better
I've saved both of your schematics
Thanks again yo han

PS
Its the people with experience that scribble a schematic diagram with no regard for accuracy or details that are a problem in a thread like this. Keep up the good work.

 

[yo han]

For someone with zero experience your doing amazingly well

Thank you very much.
I was thinking, does D1 make any sense now that I've separated the DC power to the meters?
Perhaps it'll make more sense to put it before the LM2577 module?
It's not my intention to post this thing over and over again but if I feel an update can make it easier for people to understand then it's probably better to do so here it is again. I've given the lines different colors so it's easier to see what is what.
Red = DC voltage before the LM2577
Pink = DC voltage after LM2577
Green = measuring wires from meters
Blue = GND

I've used TinyCAD to make the schematic (a .dsn file) and attached the file to this post.

View attachment welder.zip

 

[awsum140]

Yo Han, D1 was originally there to protect the LM2577 boost board. It should be moved to the positive input of the LM2577 rather than the positive input for the meters. I am assuming, which can be dangerous, that the meters have their own reverse polarity protection. For total safety, it can be placed immediately after F1 and will provide protection for anything attached to the positive input line. If you do that it would probably be a good idea to make it a 1N4004 for higher current capabilities.

Thanks for the TinyCad link, I plan on fooling with it later today. I used to have AutoCAD, up to Rev11 anyway, but it is long gone along with the need for such a sophisticated drafting program.

 

[yo han]

Thanks awsum
I didn't know what the diode was meant for but it's to protect the components in case you accidentally reverse the polarity of the DC input right?
But I've checked the specs of the 1N4004 and doesn't it have the same current capabilities as the 1N4001?
1N4001 = 1A 50V while the 1N4004 = 1A 400V
Wouldn't an RL201 = 2A 50V be a better idea? Or, because I've already ordered, use 2x 1N4001 diodes in parallel?

[edit] Just checked back a few pages and Mad Scientist said a 12V wall wart capable of delivering 583 mA would suffice to power the unit. So I guess a 1N4001 would be more than enough right? [/edit]

 

[tarnishedhalo]

Yo Han what does the F1 in your schematic represent?

 

[yo han]

That's a fuse in case anything goes wrong.

 

[yo han]

And another update.
I'm getting there. Eventually...

View attachment welder1.zip

 

[awsum140]

Yo Han, you're right about the diodes, they are both one amp, just higher voltage ratings. My mistake.

 

[tobarger]

Looks good yo han
Its moving right along

Side Note:
Ohm meter is for testing EITHER at the 510 Connector OR at Terminals 1 & 2 not both at the same time
If using to test at Terminals 1 & 2 then remove atomizer from the 510 Connector

 

[Innocuous]

stick a two-way paddle in there - left on; center off; right on

 

[yo han]

Side Note:
Ohm meter is for testing EITHER at the 510 Connector OR at Terminals 1 & 2 not both at the same time
If using to test at Terminals 1 & 2 then remove atomizer from the 510 Connector

Yes, I know. But thanks for noticing.
I'm not going to add another switch there myself but if someone else is going to build this as well then it can easily be added.

stick a two-way paddle in there - left on; center off; right on

I wouldn't use a 3 position switch in this case. left on ; right on would make more sense.

 

[tobarger]

Both DT switches are marked and appear to be On Off On
The 4PDT can be a two position switch - On On
But the DPDT switch needs to be a three position switch - On Off On
Otherwise the lowest capacitance would be 2000uF instead of 1000uF

 

[yo han]

I was referring to Innocuos' suggestion to put a 3 position DPDT switch between the 510 connector and the terminals to switch measuring between them. A 2 position On/On would be better in this case.
I wouldn't choose to make the 4PDT switch to be a 2 position switch.
First, the measuring leads for the resistance meter and both GND and positive sides of the caps are sharing the same terminals. When switching from welding to measuring with the caps still being (partly) charged, you're risking to blow your meter. I've already built in a safety measure for that but I still think it's safer to have them disconnect first and then making connection to the measuring leads.
Second, when using a 3 position switch, the middle position turns off the meters and completely disconnects the terminals so it kinda acts like an on/off switch for the unit as well (not completely because the LM2577 is still getting power of course).

 

[yo han]

Hold on! The 2577 is only needed when in welding mode.
I'm just putting the 2577 on the same 4PDT switch terminal as the V meter so when setting the switch to the off position or the measuring position, the 2577 gets turned off as well

 

[yo han]

Done

View attachment welder3.zip

Parts list on eBay incl. US shipping costs:
(Click on part name to be taken to eBay)

F1 (10 pcs) $3.50

Holder for F1 (2 pcs) $0.99

D1 (25 pcs) $0.99

R1, R2 (10 pcs) $0.99 + $1.92 = $2.91

C1, C2, C3 (4 pcs) $5.95 + $1.75 = $7.70

XL6009 (same as LM2577) $2.18

Volt meter $2.45

Resistance meter $6.64 + $1.99 = $8.63

S1, S2 $2.35

S3 (2pcs) $2.50

S4 $4.88

Total: $39.08

Remember you will still need to buy a project case, your choice of terminals, a 510 connector (or whatever you want to use) and a connector for your DC adapter plug.

 

[Innocuous]

what are the dpdt (S3) and qpqt (S4) doing? (You labeled the other switches for use).

Man, that's a LOT of switches to throw.

 

[yo han]

S3 lets you choose between 1000, 2000 and 3000 uF The higher the number, the more capacitance.
S4 is doing multiple things:
- Switches the unit on and off
- Lets you choose between welding mode and measuring mode
- Discharges the capacitors over R2 when switching to measuring mode to protect the resistance meter

There are only 4 switches this way, not that much

 

[Innocuous]

Ah. Thanks & danken sie - I thought I was seeing that. Good to know my guesses were semi-accurate ;-)

What did you end up using for a power-supply/wallwart?

 

[yo han]

Ah. Thanks & danken sie

That's German

I haven't built it yet but I've got lots of wall warts lying around. I'm going to use a 12V 1A