- Status
interesting...i just followed gsa's schematic. hmm...i guess if thats what you think caused the diode to short out. im not well versed in electronics at all...as you might of guessed.
i have the on/off switch, the charge switch and on/off LED straight from the battery into the LM2577.
Last edited:
You limit the charge of the cap by varying the voltage applied to it with the pot on the LM2577.
interesting...i just followed gsa's schematic. hmm...i guess if thats what you think caused the diode to short out. im not well versed in electronics at all...as you might of guessed.
i have the on/off switch, the charge switch and on/off LED straight from the battery into the LM2577.
Just looked at the schematic and bom and your right, the switch before the lm2577 is n.o. Momentary switch so it's only powering the whole thing for a split second.
interesting...i just followed gsa's schematic. hmm...i guess if thats what you think caused the diode to short out. im not well versed in electronics at all...as you might of guessed.
i have the on/off switch, the charge switch and on/off LED straight from the battery into the LM2577.
The charge switch should be between the diode (not needed) and the discharge cap. The way you have it wired, you essentially have 2 on/off switches in a row (series). You need to isolate the cap from the LM2577 with the charge switch
I was thinking that jmarkus was using a straight on/off switch between the battery and lm2577.....so there would be nothing from stoping voltage being applied to the cap until something failed.
It really wouldn't make any difference how long you left it on - the cap is only going to draw current until it is fully charged; there really isn't anything that would fail. The only reason he blew the diode is because there is a large initial current drawn by the cap without using a current limiting resistor.
Edit: If you look at that page that was posted for Capacitor charging, try plugging in 0Ω and see what the initial charging current is.
The problem with just an on/off switch is you have to make sure you shut it off before welding. Or it is a momentary switch.
Last edited:
If you didn't have a charge switch and had an on/off (not momentary) before the 2577, then the lm2577 would continue to output voltage correct?
I had my charge switch stick closed a couple of times when I was using a 24v power supply. So it just kept sending voltage and it kept welding until the wires got orange and fell apart. I thought the fuse on the power supply would blow but it didn't.
Ah, but you were welding at the time. Had you shut down the unit completly before welding, this would not have happened.
The fuse may not blow, since the current draw of the cap is low if it is near full charge. You are also encountering some resistance of the Kanthal. Also, power supplies are usually designed to withstand a short circuit. It's is called a crowbar circuit.
The LM2577 board may not survive this; that's why I suggest using the charge switch after the board and a current limiter.
Last edited:
The purpose of the resistor that you removed was to limit the current
With the 3.6ohm 10 watt resistor I measured the current draw at 200mA while charging the cap. This peak current for a 1n914b diode is 1amp for 1 second or 4amps for 1 microsecond. Without the resistor I am sure the cap charged faster but it surely was putting out more than 1-2amps. Since that is a slow blow fuse in there, you may have even delivered 3 amps (internal limit of lm2577) or more (probably can sustain intermittent higher current).
I put the 10 cent diode there and put the momentary switch in between the battery and the lm2577 board thinking you could get away with a very cheap switch, if it was on the output side you just need to make sure you use a switch capable of 35vdc or more, depending on what you have laying around this may or may not cost more than 10 cents
Edit: wow, you guys are posting fast. The first part was directed to jmarkus...
With the 3.6ohm 10 watt resistor I measured the current draw at 200mA while charging the cap. This peak current for a 1n914b diode is 1amp for 1 second or 4amps for 1 microsecond. Without the resistor I am sure the cap charged faster but it surely was putting out more than 1-2amps. Since that is a slow blow fuse in there, you may have even delivered 3 amps (internal limit of lm2577) or more (probably can sustain intermittent higher current).
I put the 10 cent diode there and put the momentary switch in between the battery and the lm2577 board thinking you could get away with a very cheap switch, if it was on the output side you just need to make sure you use a switch capable of 35vdc or more, depending on what you have laying around this may or may not cost more than 10 cents
Edit: wow, you guys are posting fast. The first part was directed to jmarkus...
Last edited:
Yeah I wasn't on the same page. With the camera you had a power and charge switch also, so I didn't even think about a single momentary switch in front of the 2577.
Kinda kiss if you ask me....but I bought led displays to show the 2577 output voltage and I want to see if for longer than a nano second
The purpose of the resistor that you removed was to limit the current
With the 3.6ohm 10 watt resistor I measured the current draw at 200mA while charging the cap. This peak current for a 1n914b diode is 1amp for 1 second or 4amps for 1 microsecond. Without the resistor I am sure the cap charged faster but it surely was putting out more than 1-2amps. Since that is a slow blow fuse in there, you may have even delivered 3 amps (internal limit of lm2577) or more (probably can sustain intermittent higher current).
I put the 10 cent diode there and put the momentary switch in between the battery and the lm2577 board thinking you could get away with a very cheap switch, if it was on the output side you just need to make sure you use a switch capable of 35vdc or more, depending on what you have laying around this may or may not cost more than 10 cents
Edit: wow, you guys are posting fast. The first part was directed to jmarkus...
yes, thank you....i actually added it back after i shorted the diode. so it sounds like i should be ok.
Kinda kiss if you ask me....but I bought led displays to show the 2577 output voltage and I want to see if for longer than a nano second
Just put an on/off switch on the LM2577 and a charge switch before the cap... you can still have your fancy, schmancy LED display!
Just put an on/off switch on the LM2577 and a charge switch before the cap... you can still have your fancy, schmancy LED display!
Oh I wasn't planning on letting the fancy display go to waste
I'm planning on running the 2577 off a 12v power supply I already have on the bench for my lipo charger.
The purpose of the resistor that you removed was to limit the current
Really this is not needed, the amount of current needed to charge the cap isn't that great - the fuse is enough to protect the battery. When I get mine built, I'll measure ther current draw while charging the cap and report back.
I put the 10 cent diode there and put the momentary switch in between the battery and the lm2577 board thinking you could get away with a very cheap switch, if it was on the output side you just need to make sure you use a switch capable of 35vdc or more, depending on what you have laying around this may or may not cost more than 10 cents
I wouldn't use a tactile switch here, but any Radio Shack switch would be sufficient; especially if you used a resistor in the cap circuit.
Last edited:
Oh I wasn't planning on letting the fancy display go to waste
I'm planning on running the 2577 off a 12v power supply I already have on the bench for my lipo charger.
I'm just going to go with a cheap old 14500 (I got a few AA holders laying around) and fuse it; but it would be nice not to have to drag the DMM out all the time...
I agree....here is the led meter I got....probably cheaper places but this place had both the Lm2577's and meter's and expedited shipping.
Last edited:
All true, I just like to error on the side of caution when throwing stuff out there that I know other people are going to build. Personally, I am vaping a 30 watt 7 amp .6ohm dual coil on a mechanical mod with no fuses or any protection other that what AW provides internally, so I get where you are coming from
I would be curious as to the current draw for the charging without the resistor though, I can't remember right now but I seem to recall it was going to be at least 1 amp possibly 2 amps peak. While an 18650 of any brand can easily handle that, if you were powering this box with say an old 350mA 12v power supply you had laying around you might run into the internal protection of that device. The reality is that there are probably 50 ways to build a welder now that we all understand the basic parameters of the design, a month ago that was not really the case because we had not collectively put our minds together. The design I outlined and put up the schematic and BOM for works perfectly, provided you don't start removing things or switching stuff around without understanding what does what. I got most of the parts for the second welder today and am planning on putting a step by step for it on instructables for the people who asked for it, if it is followed step by step it will give anyone a perfectly functioning machine for exactly $25 and less than 1 hour of work. There is nothing wrong with doing it a different way, just some folks like simple to follow directions without having to over think it
Ordered this. Don't know why except I like gadgets and this goes to 60v.
http://www.ebay.com/itm/DC-DC-Max-4...t_Portable_Car_Appliances&hash=item257a3aea30
http://www.ebay.com/itm/DC-DC-Max-4...t_Portable_Car_Appliances&hash=item257a3aea30
- Status
Similar threads
