CamLight System's Frigi-Mod Kit for cooling CBAs is now available

[JohnMuchow]

After doing extensive temperature measurement of a West Mountain Radio CBA II operating at higher power levels, in our opinion, it should not be operated at a level above 65W (assuming < 25C. ambient temp.). At this level, the recommended max temperature for reliable operation has been reached internally. At 87W or so, the absolute maximum operating temperature of the MOSFET (a type of transistor) that functions as the load for the discharging battery, has been reached. And this is a temperature that no device should be operated at!

We're also very concerned that the MOSFET currently being used in the CBA isn't rated for use as a load. It does have ratings for use in switching applications where it's turned fully on or off, like in an ESC, but not when it's turned only partially on to become a variable resistor load like what's done in the CBA. Most MOSFETs need to have their ratings greatly reduced when operated this way, even more so as higher voltage packs are used (down to 8% to 25% of the rating!), but the MOSFET in the CBA is operated at the full power levels used for switching applications. When a switching MOSFET not rated for this type of operation is used this way, hot spots can form (especially at higher voltages) inside the MOSFET which can lead to "thermal runaway" and quick destruction of the MOSFET. Even at power levels way below the MOSFET's rating!

But, even with our concerns, we think that the CBA is a very useful tool at a great price (we have two of them!!) and we wanted to find a way to make it more reliable at higher temperatures and power levels. To do this, inspired by everydayflyer's great fan mods, CamLight Systems has put together a kit to help reduce the temperature of your CBA by up to 40 degrees-C during a 100W discharge! Using a new fan and MOSFET, the CamLight Systems Frigi-Mod Kit lowers the temperature of the MOSFET enough to operate it at 85W-90W before it reaches the max. "high-reliability" temperature. It won't reach the absolute max. operating temp. rating until 105W-110W (limited to 100W at 40V and 95W at 48V). And, the MOSFET we've selected for use in the CamLight Systems Frigi-Mod kit is rated for the exact type of variable-resistor load use it gets in the CBA. And while nothing can guarantee that your CBA won't blow its MOSFET after making the mods, these mods will significantly lower the chance of that happening if you regularly operate your CBA at above a 65W power level.

For more info on the Frigi-Mod kit and its origins, see the following thread:
http://www.rcgroups.com/forums/showthread.php?t=939345

CAUTION: Do not attempt these modifications unless you're very comfortable desoldering parts from a circuit board, cleaning the solder off the board, and resoldering on a new part. There are two very thin circuit board traces running from one of the MOSFET's pads and if you overheat that pad, the traces can become damaged.

Please note the following:
- Performing any of the modifications that are part of this kit immediately voids the warranty for your CBA.
- These mods do not guarantee that your CBA won't blow in the future! Operating at high temperatures stresses the MOSFET considerably and it can blow in 2 seconds or 20 years. There's no way to tell. But, the lower the temperature of the MOSFET, the longer it lasts.
- I am not responsible for any damage to your CBA that occurs while doing these mods or while operating the CBA after the mods have been completed. They has been tested thoroughly here at CamLight but we cannot guarantee the results on your CBA.
- You must have a 12V-13.2V, 750mA (or greater), regulated DC power source for the new top fan. The fan draws about 0.5A. This fan cannot be powered from the USB port as the CBA's on-board fan is.
- The fan is warrantied for one year but there is no warranty for the kit's MOSFETs. Each one is tested and confirmed to be working before it is bagged and sent out as part of the kit. Their sensitivity to static and overheating means I cannot be held responsible for any damage to them during installation. Please proceed carefully when installing the MOSFETs, making sure you have dissipated any static charge you're carrying.
- You will need the following tools to perform the mods; power drill, 1/8"-3/16" bit for screw and side air holes, 1/4"-3/8" drill bit for bottom air holes, #2 phillips screwdriver, good soldering iron with grounded tip.

The CBA Frigi-Mod Kit is priced as follows:
Option 1 - Complete Frigi-Mod Kit* = $19.99 + $4.75 Priority Mail shipping = $24.74
Option 2 - Two IPP048N06L MOSFETs** = $6.99, First Class postage included. Cost is $5.99 if adding Option 2 to Option 1 purchase.

Ordering Option 1 gives you the complete mods kit. You only need to order Option 2 if you already have a fan+hardware you'd like to use or if the MOSFET-only temperature reduction is enough.

Payment can be made via Paypal or check/money order. If paying by check/money order, I'll send out your kit(s) as soon as it clears. Please contact me by PM for my PayPal account address or mailing address and include your mailing address in the PM.

*The complete kit includes the following:
- Replacement 12V Delta fan
- Two IPP048N06L MOSFETs in an anti-static bag
- 2" length of desoldering braid.
- Small packet of thermal compound to mount MOSFET.
- Four 1-1/4", #6 sheet metal screws for top fan.
- Four 1-1/4", #6 machine screws for bottom fan.
- Four 3/8", #6 nylon spacers for bottom fan.
- Four #6 acorn nuts for bottom fan.
- 70mm metal guard for bottom fan.

**You do not need to order these separately if you're ordering Option 1 as two MOSFETs are already included.

[Edit] The brown wire going off to the right in the photo is from the thermocouple reading the MOSFET's temperature.
[Edit] Lots of various changes, please re-read before ordering if you haven't read it in a while.

[dmimlitch]

John

I just bought a CBA II and have not received it yet, but I want it to last. I am just a bit unclear as to what I need to order.

The CBA Frigi-Mod Kit is priced as follows (plus $4.75 Priority Mail shipping):
opt 1- New top fan + two IPP048N06L MOSFETs = $14.99
opt 2- Accessory/Hardware pack*** = $3.99
opt 3- Two IPP048N06L MOSFETs = $5.99



If I order the first option and the second option, do I need the third? Should I order the third just so I have spares? I am guessing that the third options is for people that have already done a fan mod.


Thanks for the help and thanks for making what looks like a good product even better.

Dave Mimlitch
Carrollton, tx

[Al Offt]

Dave,

<ref: If I order the first option and the second option, do I need the third? Should I order the third just so I have spares?>

I can answer that qustion with a No. When you order Opt 1, you get two MOSFETS: one to replace the stock one in the CBA and the second a spare just in case you break the first one (through static discharge or whatever) in the process.

Opt 3 is a courtesy John extended to me (and others) when I requested two more MOSFETS.

Alan

[JohnMuchow]

<snip> If I order the first option and the second option, do I need the third? Should I order the third just so I have spares? I am guessing that the third options is for people that have already done a fan mod.


Thanks for the help and thanks for making what looks like a good product even better.

Dave Mimlitch
Carrollton, txThanks Dave!
Yea...umm...what Al said. :)

John

[JohnMuchow]

I've uploaded the instructions for the Frigi-Mod Kit.

http://www.camlight.com/techinfo/CamLight_Frigi-Mod_Kit_Instructions.pdf

John

[JohnMuchow]

V1.10 of the instructions have been uploaded. This adds a step to Method Two of the MOSFET mod portion to tell the user to solder in the new MOSFET. :o

John

[JohnMuchow]

<arrgghhhhh>
I have received two of the three shipments of parts for the Frigi-Mod Kits. I tracked the third shipment and it won't be here until Tuesday so unfortunately the Kits will be going out on Wednesday, two days later than planned.

Sorry. :(

Why one UPS Ground shipment can get from California to NYC in 3 days, but the one from Minnesota takes 7 days, I have no idea. :mad: :censored: :mad:

John

[JohnMuchow]

I have received all of the parts a day earlier than I thought I would and the 4 kits that were ordered will be in Tuesday's mail. After buying parts for 25 kits, to get everyone's price down, I was hoping to move a lot more than 4 kits but hopefully WattFlyer and RC Universe will take a bunch. :)

John

[JohnMuchow]

The kits shipped out on Tuesday and hopefully everyone gets theirs before the weekend.
Please post your experience doing the mods when you're done! :D

John

[dmimlitch]

I just got mine. Sweet just in time for the weekend.

Thanks you John

[JohnMuchow]

Excellent!

I forgot to mention that there is an extra set of spacers in the kit. The shorter set is for use with the bottom fan guard. The longer set is used if you don't want the bottom fan guard in place. I don't know why anyone would skip using the bottom guard but I accidentally ordered the wrong length spacer but threw it in anyway. :o

John

[ebill3]

Speedy shipping, excellent packaging, correct parts, up and running at 6 PM PST 11/7/08. And I have a spare MOSFET.

Thanks, John.

Bill

[Al Offt]

Sorry I did not reply earlier. Got my kit at the end of last week (or was it two weeks ago?). Thanks for the quick delivery. I plan to work on the mod this weekend after I correct an issue with my older computer (appears it was close to its speed limit, parts aged and had to adjust BIOS settings).

I would like to be able to test batteries at the max limit of 150watts so I'm going a slightly different direction. I bought two large heat sinks from the local electronics shop and plan to make a sandwitch with them as the bread (fins out) and two MOSFETs (separated laterally and wired in parallel) as the meat. The kit's fan will blow air through a box tunnel across both heatsinks and down the space between them. I'm looking to cool both top and bottom of the MOSFET as well as to make sure I get the whole surface of the MOSFET snug against the heatsink.

If that does not work for whatever reason, I have two more MOSFETS to perform the mod as designed. I'll take pictures and post them.

Alan

[write2dgray]

Sounds interesting Alan, I look forward to seeing some pics of your more extreme solution.

[JohnMuchow]

Alan, definitely post pictures and the results of your testing!

John

[Al Offt]

Here are three pictures showing the beginning of the mechanical assembly to give you a better idea about the FET sandwich. I did mention that the heat sinks were surplus, didn't I :D . Had to cut off two fins worth of extra width but they had a bunch of holes predrilled and tapped so I used two of them for initial mounting of the FETs. I drilled two holes right next to the FETs (between fins on the other side :p ) and tapped the hole on one side to accept the 4-40 screw - had to grind the screw heads to fit between the fins. The long screws show those positions.

Second picture shows how both sides of the heat sink go together so the FETs don't lie on top of each other. The third picture shows how the heat sinks will be positioned next to the fan. Haven't made the heat sink shroud yet but when it's done, it will have tabs folded over on which to mount the fan. All that will sit next to the CBA (since its USB cable exits in the back while the battery leads are in the front).

Alan
BTW The T0-220 chips in the picture are 5v regulators. I do not trust using the MOSFETs because of static discharge.

[JohnMuchow]

Nice Al!
As long as the FETs cooperate being in parallel, I think that set up will keep them a LOT cooler than the stock CBA setup. If you can, give the FET mounting surfaces a going over with 000 steel wool to deburr any tiny scratches on the surface of the heat sink. Even burrs a couple of mils high will significantly reduce the mating between the heat sink and the FET.

Using a shroud is a great idea. It will significantly increase the effectiveness of the fan cooling of the sinks.

John

[Al Offt]

Hi all,
I have to apologize to any of you waiting to see if my approach will work. I've read a bunch about paralleling MOSFETS on the web and determined some design parameters based on objectives:
1. Since the SW will only allow 150W on startup and the fuse inside the CBA is 40amps, I decided to design for 20 amps max through each MOSFET.
2. To reduce an imbalance of current sharing, I plan to place a 0.02 ohm resister (some yet to be determined length of small diameter wire) in series with the source lead of each external MOSFET - i.e. two resistors, one to each MOSFET.

As mentioned earlier, the idea for these resistors is to help balance current between MOSFETs. Since the 'on' resistance of the MOSFET depends on the voltage difference between its gate and source and both gate voltages are the same, if more current passes through one MOSFET than the other, that current will cause an increase in source voltage for that MOSFET (relative to the other), reducing the gate to source voltage; thus, increasing the resistance of that MOSFET. Sensitivity should be decent since the gm (IIRC, change in drain to source current per change in gate to source voltage) of the MOSFET is around 100 (but probably not at our voltage/current levels) so a 0.01 volt increase in source voltage should cause a 1 amp decrease in current. To test for gate headroom, I'm designing for a total of 0.4 volts change from 0 to 20 amps through one MOSFET.

A lot of uncertainties at this point. I need to take a bunch of measurements on the current CBA's MOSFET to determine set points at different current levels and the voltage drop across the internal sense resistor (also 0.02 ohms from what John wrote). Next step is to determine what length of flexible 'small' wire causes a 0.4 volt drop at 20 amps (and can dissipate 8 watts). If all goes well, I will then wire up one external MOSFET with its individual source resistor to see if I have the gate voltage headroom and sensitivity to make the idea work.

More after Thanksgiving,
Alan

P.S. Please don't assume I know what I am doing with MOSFETs. I have experience with NPN transistors, not MOSFETS so my assumptions about how they work may be faulty. I'll find out.

For those of you electronically inclined:
Parallel MOSFETs in linear operation: http://www.nxp.com/acrobat_download/applicationnotes/APPCHP1.pdf, page 52
Eliminate Oscillation in parallel MOSFETs: http://www.microsemi.com/micnotes/APT0402.pdf

[JohnMuchow]

Great work Alan! You've done some terrific research and I'm very interested in seeing how this turns out.

The IPP048N06L selected for the Frigi-Mod Kit isn't a linear or planar MOSFET, as in the app notes, but it's spec'd for linear operation so I'm really hoping it works. It would give CBA owners another option for really, really bringing down the operating temperature of the MOSFETs and allow reliable continuous 150W operation (the CBA's software limit).

There are two 3W, 10mOhm current sense resistors in the CBA. But for some reason I'm remembering that they take the sense voltage from between the resistors, not from the top of the two. It might be worth a double check of the PCB to make sure.

Another doc about paralleling MOSFETs...for those of you REALLY like math:
http://www.irf.com/technical-info/appnotes/para.pdf

John

[Al Offt]

Thanks for the sense resistance information. I was puzzled by the thin trace between the two thick ones and what looked (from the copper trace side) like resistors in series. Your information solves that mystery.

Alan

[JohnMuchow]

For the life of me though, I can't figure out why they would have two sense resistors but only sense from one, especially if only using a single MOSFET. I must be missing something very obvious here. :)

Maybe double-check and probe those traces to make sure I traced them correctly. :o

John

[gulio]

I just got my Mosfet mod done. It went very well and will soon run a few low power runs in the cool garage. Fan kit to follow.

Mind you I've not soldered components onto a board before. Thanks to John's excellent instructions and attention to detail and complete kit it worked good and I'm very pleased.

I'd heard of desolder braid before , but had never used it. It works slick. I used method 2 and soldered before applying the paste. It makes for one additonal r&r of the board, but no matter because things lined up perfectly. I'm not the best solderer , but it looks like it was done by a pro. (sorry no pics) :(

Nice mod, I recommend it.

[Gus]

This morning I installed the Frigi-Mod that I received from John.

I elected to do Option 2 (I felt that it was a cleaner Modification). Everthing went very well, and I completed it in around 30 minutes. I had no problems, and everthing was as the instructions stated.

I spent another half hour or so testing the completed mod with no problems at all.

I am very happy with the Modification to the CBA II.

Gus...

[gulio]

2 questions :

How does the cba check temp (for giving the error message and shut down) where is it reading temp?

On the bottom fan , the idea is to blow air over the mosfet and components of the cicuit board right? Where is the outlet for the air? Is it to exhaust out of the side vents and holes?

I did mine a bit differently wanting the exhaust to be around the top edge of the circuit board (outlet above the board by the heat sink).

[gulio]

Since I'm asking questions :

would the unit work better inverted? and/or
would the unit work better with either/both fans in reversed direction?

[JohnMuchow]

The unit runs approximately 8C hotter when inverted and the unit will run MUCH hotter if the top fan is reversed and a bit hotter if the bottom one is.

The top fan, if reversed, will only pull cool air past the tops of the fins, significantly decreasing the heat sink's effectiveness). When pushing the air down, the cool air gets to all of the surface of each fin and is much more effective. My CC-400 load uses its fan in "expulsion" mode, i.e., pulling up, but there's a shroud coming a decent ways down the heat sink to force the air into the bottom of each fin before being pulled up.

The bottom fan needs to blow air into the hole in the PCB which the MOSFET is mounted in and if the fan was reversed, a lot less air will move past the bottom of the heat sink unless the case mods are done very, very carefully.

Regarding your first post...
IIRC, the CBA has a component on the circuit board that checks for ambient/board temperature. There's nothing connected to the heat sink to check the temp of the MOSFET or sink. Unless they're monitoring the voltage drop across the MOSFET as it heats up (a decent way to detect its temp), but I'm not sure.

The bottom fan's principal function is to blow air over the bottom PCB to prevent the fuse and fuse holders from dropping out at high current levels and also to blow air past the MOSFET and in between the heat sink and PCB. The exhaust holes/slot should be located between the heat sink and PCB. It's mentioned in the instructions (Step 11b, IIRC, in the bottom case mods section). Your setup positions the exhaust perfectly.

John

[JohnMuchow]

The top fan for the Frigi-Mod Kit is only rated up to 13.2V. Please only use a power supply or pack with an open-circuit (disconnected) voltage of 13.2V or less.

Do not assume that a 12V wall-wart you might use is regulated and outputting only 12V! Many wall-warts are unregulated and can often be above 15V before the fan's current draw might drop the voltage down. But the fan's controller IC can burn out wayyyy before this.

Two fans have burned out so far by being connected to a power supply at 15V or higher. Please only use a regulated 12V supply or pack that never, ever exceeds 13.2V.

Thanks!
John

[gulio]

:o Uh, both fans were all my fault:o
John graciously took care of me. Thanks.

for some reason I didn't get notice of replies close to this date.

And thanks for the answers about the cooling, that makes sense.