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Voltage drop on a box mod

1000moths

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Aug 18, 2014
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Hi,

I finished my first box mod, it's got 2 18650's in series going into a LM2596S DC-DC stepdown module.

The switch is fitted to a MOSFET (IRF540A MOS-FET Transistor TO220 Case | Maplin) so it doesn't die with the amount of amps coming from the duals.

I've got a Volt display connected to the 510 connector.

Without and atty attached it shows 7.6v (lower than i'd expect) but when I attach any atty it drops to 4.9 max.

Any ideas what ive done wrong?
 
I am not very familiar with the LM boards, I have one but yet to build with it. Others may be able to help more than me but a bit more info would be useful.

What voltage do you have at the batteries when under load?
What is the resistance of your atty?
What is the voltage at the gate(G) on your FET?
Does adjusting the LM board make any difference?

Can you also show us some pics of your circuit and do you have diagram you have followed?
 
Hi,

I finished my first box mod, it's got 2 18650's in series going into a LM2596S DC-DC stepdown module.

The switch is fitted to a MOSFET (IRF540A MOS-FET Transistor TO220 Case | Maplin) so it doesn't die with the amount of amps coming from the duals.

I've got a Volt display connected to the 510 connector.

Without and atty attached it shows 7.6v (lower than i'd expect) but when I attach any atty it drops to 4.9 max.

Any ideas what ive done wrong?


From memory,I believe the LM2596 PCB is only rated at 5-6 amps(maybe even less)which could be why your seeing such large voltage drops.I have a couple of these boards & was hoping to use them in my boxes,but I had to run the cells in series to get it to work & when I was adjusting the voltage I nearly removed several layers of skin as the components on the PCB were that hot.
 
From memory,I believe the LM2596 PCB is only rated at 5-6 amps(maybe even less)which could be why your seeing such large voltage drops.I have a couple of these boards & was hoping to use them in my boxes,but I had to run the cells in series to get it to work & when I was adjusting the voltage I nearly removed several layers of skin as the components on the PCB were that hot.

That's likely it then, as the voltage only drops once an atty it attached, and the volt reader is attached to the 510 so i'd be surprised if it's a problem with the circuit.

Any alternatives to the lm2596 that anyone could recommend?
 
That's likely it then, as the voltage only drops once an atty it attached, and the volt reader is attached to the 510 so i'd be surprised if it's a problem with the circuit.

Any alternatives to the lm2596 that anyone could recommend?

My workaround was to abandon any notion of varying the power until I found a source of PCB that could output upto 200 watts, I did find the circuit diagram to build my own but the main chip(naos raptor or alternatives)was proving elusive in the UK(then impossible as the supplier I intended using ceased stocking)

posted from a DIY juice cloud
 
Fair enough I guess I'll just wait for the 100w sx350's or whatever comes out

Sent from my SM-G900F using Planet of the Vapes mobile app
 
Fair enough I guess I'll just wait for the 100w sx350's or whatever comes out

Sent from my SM-G900F using Planet of the Vapes mobile app

Apparently, later this year a 200 watt sx type device is due. If they do, I'll be in there straight away as I love my present 0.14 ohm RDA powered from 4000 mah lipo pack:D

posted from a DIY juice cloud
 
Apparently, later this year a 200 watt sx type device is due. If they do, I'll be in there straight away as I love my present 0.14 ohm RDA powered from 4000 mah lipo pack:D

posted from a DIY juice cloud
ETA December but you know ETAs ;-)
 
I've looked at the raptors and am considering getting some shipped in from the USA. In the meantime I'm going to try an OKR 10 amp chip and see how that fairs.

Sent from my SM-G900F using Planet of the Vapes mobile app
 
From memory,I believe the LM2596 PCB is only rated at 5-6 amps(maybe even less)which could be why your seeing such large voltage drops.I have a couple of these boards & was hoping to use them in my boxes,but I had to run the cells in series to get it to work & when I was adjusting the voltage I nearly removed several layers of skin as the components on the PCB were that hot.

I use one of these boards and i believe they're only rated at 3 amps so if you use a low ohm build on them the voltage drops.
I've seen a 60A 300W raptor type chip on the box modders group FB page but i cant find the bloody thing now, i'll keep looking and try to find a link.
http://apps.geindustrial.com/publibrary/checkout/NSR040A0X?TNR=Data Sheets|NSR040A0X|generic 40A 200w raptor.
https://www1.elfa.se/data1/wwwroot/assets/datasheets/D12S300_eng_tds.pdf, 60a one.
https://www.facebook.com/photo.php?fbid=700791996656062&set=p.700791996656062&type=1&theater for a diagram if you have FB.
 
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