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Little Big Project

fasteddie600

Mod Maker
Joined
Jul 15, 2014
Messages
372
Inspired by @Seedy and the pocket rocker mod, the good lady was going to get a wee box mod today. Unfortunately that box got ruined when I drilled the wrong side so that ruined my plan for a tiny box mod with a single battery.
So instead I built this with the time today.

2dik11k.jpg


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It's a bit of a plain jane on the outside except for the brilliant FDV 510 which is fantastic having sprung centre post.
Fitted inside it has 4 Turnigy Lipo power packs each rated at 35C continuous 100C pulse. Wired in parallel that gives over 100A handling continuous. 750mAh each gives it 3000mAh and an onboard 1A USB charger.
Switch is wired via 68A(continuous) MOSFET and 2.5mm wire.
Unfortunately no room for a fuse or a power switch, but I can live with that as it's only for me to use. I wanted an LED in there too but I gave up figuring out how to make a neat job of that with so little space.

Interestingly this has a much lower volt drop than my big power project box mod running 2xVTC5's! Aprox 0.3V better in the Lipos with a 0.13ohm coil running around 80-90W.

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I am happy, for a box that took 6hrs to build and cost under £30:yahoo:

Turnigy Batteries from Hobbyking @£1.90ish each
Box from maplins £3.09-not the greatest!
FDV 510 from Modmaker £5.99
Switch from RS £8.99 I pushed the boat out a bit there!
Mosfet about £1.50 from RS
USB board from Modmaker £1.99
Resistor about 2p and some wire.
£29.18

Not sure how many box MOD's I need but it is definitely more!:eyeroll:
 
Whole thing looks pretty good. .. to a non technical person the insides as always looking a bit scary
.. but hey it works and looks good. .. major success

Sent from my GT-I9505 using Planet of the Vapes mobile app
 
volt drop may be due to battery sag, lipos sag less @fasteddie600

I had expected the Lipos would perform better, but didn't expect such a big difference. 10W extra(2xVTC5 v Lipo pack at 0.2ohms) is enough that I can tell just by the noise!

Whole thing looks pretty good. .. to a non technical person the insides as always looking a bit scary
.. but hey it works and looks good. .. major success

Sent from my GT-I9505 using Planet of the Vapes mobile app

The insides are actually pretty simple, everything (except the last connection on FET and 510) has been heat shrunk/wrapped to avoid any possible contact with everything being so close together.
 
Finally found some time to do some destruction testing on both boxes today. I now have a coil/FET graveyard;)

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Testing has required a change of underwear! I got down to 0.07ohms then the FET on the Little box got stuck on and I had no way to shut the damn thing off and an atty kicking out 150W that I couldn't get near to remove. Thankfully the coils melted quite quickly otherwise it was about to be launched down the garden. I did have a fire extinguisher to hand(yes really) but that gets really messy.
I now have a new appreciation for FET's being in metal boxes! They can get really feckin hot! The total failure has melted a bit on the top of the plastic box, but hey £3 is not worth crying over and I now know where this circuit will go to.
The lipo batteries however didn't even get warm! So the FET's are the limiting factor on both MOD's and neither will really take the capacity that the Data sheet's would seem to suggest. I am no expert so maybe someone out there can enlighten me if I am doing anything wrong!

Bit more testing once new FET was fitted in the little box(uprated one for 110A). These are the results.

Little Box Safe atty load 0.2ohms+ (72W at full charge)
Big Box Safe atty load 0.18ohms+(72W at full charge)

I have used both down to 0.13ohms without issue, but that is getting a bit too marginal for my liking.

As always testing these boxes will be ongoing, at least now I am happy I am using the boxes more safely.
 
Finally found some time to do some destruction testing on both boxes today. I now have a coil/FET graveyard;)

261nc69.jpg



Testing has required a change of underwear! I got down to 0.07ohms then the FET on the Little box got stuck on and I had no way to shut the damn thing off and an atty kicking out 150W that I couldn't get near to remove. Thankfully the coils melted quite quickly otherwise it was about to be launched down the garden. I did have a fire extinguisher to hand(yes really) but that gets really messy.
I now have a new appreciation for FET's being in metal boxes! They can get really feckin hot! The total failure has melted a bit on the top of the plastic box, but hey £3 is not worth crying over and I now know where this circuit will go to.
The lipo batteries however didn't even get warm! So the FET's are the limiting factor on both MOD's and neither will really take the capacity that the Data sheet's would seem to suggest. I am no expert so maybe someone out there can enlighten me if I am doing anything wrong!

Bit more testing once new FET was fitted in the little box(uprated one for 110A). These are the results.

Little Box Safe atty load 0.2ohms+ (72W at full charge)
Big Box Safe atty load 0.18ohms+(72W at full charge)

I have used both down to 0.13ohms without issue, but that is getting a bit too marginal for my liking.

As always testing these boxes will be ongoing, at least now I am happy I am using the boxes more safely.

were the fets heatsinked ? dropping small volts at high current amounts to a lot watts dissipated as heat
 
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