5x26500 Mosfet Mag keeps flashing bulbs

[ellum68]

After waiting six weeks for my KIU socket, I finally got to fire up my Mag build tonight. I'm running 5xIMR26500 cells using a Mosfet setup as detailed by Petrev http://www.candlepowerforums.com/vb/showthread.php?t=182482 . It was quite a chore getting the thing together. I tried 64440 and 64447 bulbs and flashed each one after about one second after switching it on. Am I running too much voltage or did I screw up something when I built the mosfet? These were the IRC bulbs. I had a 64458, but cracked the glass before I got to install it. Theres nothing like wasting $20 worth of bulbs in one evening.

 

[mrartillery]

How much voltage do you have at the bulb socket pins? 5x 26500's shouldn't flash a 440 or 458, I have the same setup and no to date.

 

[ellum68]

I actually just tested that. I have about .6v with the switch off and 20.69v with it on. There is zero continuity between + and - on the switch assembly when the batteries are removed. I worried about my job on the Mosfet because everything was just so darned crammed when assembling. I added a copper braid to the tailspring and made sure all my solder joints were robust in the Mosfet, so resistance should be minimal. I didn't get to try the 458 as it got broke before install. The 440 and 447 were the IRC eco variety. I'm wondering if the heat simply melted the filament. The 440 seemed to melt and the filament fell from both ends when I powered up.

 

[mrartillery]

The problem you're having is due to the fact that Lux's test were done in "soft start" type setting with voltage added gradually. The 440 is a 12v bulb and when you all of a sudden throw almost 21v to it, they sometimes have a tendency to go , not all of the time but some. Plus this bulb only uses around 5.5a which doesn't pull the 26500's down near as quickly as the 458 will at around 10a.

 

[ellum68]

Thank you for the reply! This mosfet setup is actually a make do piece until AW gets more softstart units done. It looks like I need to get a 64458 comming and not break this one. I might try a 64432 as well as it seems to be able to take a healthy amount of voltage.

 

[mrartillery]

You should be able to power the 440 with no problems with a soft start, once the filament is hot it greatly reduces its chances of flashing it. Although, be careful when using the 458 with the soft start, the 458 is a 90w bulb but when overdriven it reaches over 212w. The AW is only recommended for bulbs up to 200w, but you should be okay if you use it in short bursts and not extended runs.

 

[ellum68]

Well, the 458 showed up today and it works perfectly. I can't wait for dark. It appears the IRC 440 and 447 simply can't hold up in a low resistance direct drive application. The heat is too much and the filaments just melt.

 

[mrartillery]

Well good Im glad it worked out for you. I think you will be well pleased with the 458, I currently am using this bulb in two different hosts with 2 different battery configurations, a 4d with 5 IMR 26500's and a quad bored 4d with 16 Elite AA's. Its one of my favorite hotwire bulbs, for good reason. Now, if you really want to step up your game get your self a throwmaster or one of FM's FM-3's. The 458 makes a beautiful round hotspot that throws a long way.