PWM or DC-DC?

[conanthewarrior]

Hi people, I was flcking through the instructions and saw I can change from PWM to DC-DC, I have tried both and can't really tell a difference.

What does the sigelei 30 watt use out of the box? DC-DC or PWM? As I will probably stick to that, not noticing and difference between the two.

 

[Tim Vatic]

DC-DC is a smooth flat line output
PWM or (pulse width modulation) is a Pulsed output.

DC-DC is the most accurate but yes, its difficult to distinguish between the two.

 

[conanthewarrior]

Hmm, which do most people use? I have read PWM may give longer battery life? Also my device comes standard PWM apparently, so I think I will use that as I have been using it for the past week in that mode and enjoyed it, so think I will leave that alone and keep it pulsed.

 

[conanthewarrior]

Ahhh I have found DC-DC mode on my device bypasses the chip and turns it into a mechanical mod, allowing you to fire lower than it would allow. I think I will stay PWM for the safety features.

 

[conanthewarrior]

AM I correct that the DC-DC bypasses the chip as I have read online, or is this wrong? As I am sticking to PWM if it is safer and have been using that.

 

[SteveZ]

I believe that is wrong. In DC-DC mode the chip will still regulate the voltage up if it needs to but it won't go lower than the battery's current voltage level no matter what the display says. In PWM mode the chip will use DC-DC mode above the battery's current voltage level but will vary the width of the voltage pulses to go below that voltage when it needs to based on your wattage setting and atty resistance. Phil Busardo demonstrated this with a scope in one of his reviews and I think other reviewers have confirmed this behavior.

In general, PWM is the way to go unless your settings and resistance puts your voltage on the border and you want to make sure the device chooses DC mode.

 

[conanthewarrior]

OK I will stick with PWM, I am pretty sure that is the standard setting as I had to put it in Dc-dc mode, it must of been PWM before that, and I was enjoying it fine so will stick with that. Clever stuff how it can go lower than the batteries actual voltage, I did wonder how it did that (And how it got over 7volts out of it) But I guess it is the magic in the box lol

 

[SteveZ]

Hehe, it does seem like magic sometimes. I understand in principle how they do both but to design a circuit to do that is way beyond my poor skills.

 

[conanthewarrior]

I have read of the 'rattlesnake effect' some PWM mods have. I haven't noticed my mod any different frrom dc-dc to PWM, so It's either not a 33HZ chip, or I just can't tell lol.

 

[conanthewarrior]

Right, just to double check, If I use DC-DC, it is still safe? Like If I used too low watts on an atty, it won't go wonky on me, or should I stick to PWM for safety, (have been using PWM, It was funny dry firing the coils, you could hear it cycling on and off, sounded kind of like a tazer lol) I can't really tell a difference between PWM and DC-DC, apart from say I choose 17 watts at 0.9 Ohms, on PWM it will read 4.0V, while DC-DC reads 4.2V.

 

[SteveZ]

I am assuming your battery is fully charged. at 17 watts and .9 ohm resistance you would expect about 3.9-4 volts which is what the PWM is giving you. In the DC-DC mode you get a minimum of battery voltage, thus the 4.2 volts. That means that you are actually getting almost 20 watts in spite of what you have the device set to. That is ok as long as your atty can handle the 20 watts. As the battery drains the watts will drop until it hits the 17 watts then it should stay there until the battery is completely drained. If you want to get the wattage you set the device to, you need PWM. But DC-DC will work most of the time. I think you would tend to get in trouble with a low ohm resistance where you want a relatively low watts. In that case the DC-DC will give you a radically different actual wattage much higher than you have set.

 

[conanthewarrior]

I am assuming your battery is fully charged. at 17 watts and .9 ohm resistance you would expect about 3.9-4 volts which is what the PWM is giving you. In the DC-DC mode you get a minimum of battery voltage, thus the 4.2 volts. That means that you are actually getting almost 20 watts in spite of what you have the device set to. That is ok as long as your atty can handle the 20 watts. As the battery drains the watts will drop until it hits the 17 watts then it should stay there until the battery is completely drained. If you want to get the wattage you set the device to, you need PWM. But DC-DC will work most of the time. I think you would tend to get in trouble with a low ohm resistance where you want a relatively low watts. In that case the DC-DC will give you a radically different actual wattage much higher than you have set.

Ok, PWM seems the way to go then. I think its what my device come set as, so I will keep it on that instead of dc-dc. What benefit does DC-DC offer in a vaporiser (not mechanical mod) as it seems like PWM has most of the advantages

 

[SteveZ]

Except for border cases I really don't understand the DC-DC only mode given that in PWM mode the device will automatically and silently switch to a straight DC output when it needs to boost the voltage.

I always leave my devices in PWM mode.