Measuring amps.

[Chegs]

I found a similar issue with my 1st "thrown together" battery box,tested for voltage drop & got some pretty dire readings.Added 2 batteries in parallel & tested again,result was the 2nd battery was able to overcome the resistances (I never found exactly where the resistance was high) and my RDA worked as well on the cobbled together box as it did on the proper mech tube.

 

[RicModMaker]

The dna20 draws 7a and they suggest using 22 gauge cable iirc. For a direct cell to atty type box, I would want to go much bigger. Mains cable is one option. Or go to an rc shop and buy a couole of handfuls of rc racing car motor cable. Its very flexible and can take proper high current.

The wire I'm using is 16AWG auto wire so I thought it would be good enough. It's pretty thick stuff.

 

[RicModMaker]

I found a similar issue with my 1st "thrown together" battery box,tested for voltage drop & got some pretty dire readings.Added 2 batteries in parallel & tested again,result was the 2nd battery was able to overcome the resistances (I never found exactly where the resistance was high) and my RDA worked as well on the cobbled together box as it did on the proper mech tube.

I defo think mosfets are the way to go.
Been reading up loads lately but am still a bit baffled as to what ones to use and how to wire them up.
More reading needed unless you'd be good enough to do a quick sketch for me Chegs?

I'd like to do one with a single 18650, 1 with 2 x 18650 in parallel and 1 with 2 x 14500 in series.
All with tactile switches but am not sure which mosfet type and size to use and where to put resistors etc.

Choices choices choices. Enjoying the learning though so it's all good.

 

[Chegs]

Best place I can think of right this very second,to learn about MosFets would probably involve a hunt round Breaktru's site,I'm off out very soon so no time time to research & post links Seedy sorry mate.

 

[doobedoobedo]

I use these:http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1688590

and wire them up like this:

 

[jcol]

I use these:http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1688590

and wire them up like this:

Thanks for posting that pic.
Is it a normal 15K resistor? as doing a quick google search is throwing up some all with different values
(sorry for the noob question lol)

 

[doobedoobedo]

The value of the resistor doesn't really matter, all it's there for is to pull the gate back down to 0V when the switch goes off, just don't use one that's too low a resistance.

My all day mod does without the switch completely. By using a massively high resistance (I use 47Mohm, higher is better) you can use a finger to make the circuit creating a resistive touch switch. Only down side is no metal drip tips .

 

[RicModMaker]

I use these:http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1688590

and wire them up like this:

Top man. Exactly what I'm after.
Can you tell me what relation the resistor has to the battery voltage. If I wanted to use 2 batteries in serial would anything need to be changed? I'm guessing that I'd need to double up the resistance.
:-)

 

[RicModMaker]

Sorry for the questions @doobedoobedo
When I get the resistors, do I need to get high wattage ones? There are so many 15k resistors out there.
Can I use a standard 6mm tactile switch?
Can I use a low amp slide switch?
I'm guessing I can beacause the high amp current won't be flowing through these switches. Can you confirm please?

Thanks again for your help. It's very much appreciated.

 

[doobedoobedo]

Top man. Exactly what I'm after.
Can you tell me what relation the resistor has to the battery voltage. If I wanted to use 2 batteries in serial would anything need to be changed? I'm guessing that I'd need to double up the resistance.
:-)

It's simply ohms law . With 4.2V you'd get a current of 0.28mA across the resistor, with 8.4V double that. So still negligible.

Sorry for the questions @doobedoobedo
When I get the resistors, do I need to get high wattage ones? There are so many 15k resistors out there.
Can I use a standard 6mm tactile switch?
Can I use a low amp slide switch?
I'm guessing I can beacause the high amp current won't be flowing through these switches. Can you confirm please?

Thanks again for your help. It's very much appreciated.

No need for high wattage resistors, see above. If you have any resistors kicking about work out the current leakage across them with ohms law, if it's acceptably small, then go for it.
You can use any switch you want, the current is so low, as I mentioned . That is one of the biggest advantages of separating the high current side from the switch.