Semi-custom shark?

[wvaltakis2]

Wayne,

I'd like to get a shark setup with a max output of 300 ma and the pot removed for an external pot. Is this possible and how much would it be? Also, could you please point me in the direction of a pot suitable for mounting in a Mag? Thanks in advance.

~Chip

 

[wvaltakis2]

bump

 

[Greg G]

The Shark has a .1 ohm sense resistor in it. You can swap it out with a different one to get the current down. I'm getting ready to do just that on a Shark that is going in a headlamp I'm building. I want to limit the current to 500ma max.

On the pot, get a 20k logarithmic version. There are lots of them around made by different manufacturers. I bought a few the other day from a local shop.

Wayne is out of pocket at the moment. He'll be back soon. He can give you more defined answers about the right value for the sense resistor.

 

[wvaltakis2]

Thanks, I'll wait for his input on the value and whether or not he'll swap e'm (they're SMD if I remember right). I check Radio Shack and Hobby Town today, the only thing small they had was a 10k volume wheel Could someone just point me to a specific part I could order?

~Chip

 

[Greg G]

Digikey has lots of them. Someone posted a link to a 20k pot that would easily fit into a mag, but is was a linear pot IIRC. I don't know how it would work. I went with a logirithmic pot because that's what some other more experienced guys here said to get.

I would do a search. Use the google function up top, and check off the box that says to search CPF only. Type in "20k pot" and you'll some results you can read through.

Good luck.

 

[dat2zip]

Wayne,

I'd like to get a shark setup with a max output of 300 ma and the pot removed for an external pot. Is this possible and how much would it be? Also, could you please point me in the direction of a pot suitable for mounting in a Mag? Thanks in advance.

~Chip

The sense resistor used on the Shark and many other boards follows the resistor values according to the E12 range.

See this chart (yellow column) here.

The closest value would be 0.33 and I have those if you want them swapped.

Since I have not seen this request very often I will do this for you for free. If you order the Shark and select the remove trim pot option and then in the order notes put the request to change the sense resistor to 0.33 I can change the sense resistor at the same time I remove the trim pot.

I would really recommend others should reduce the sense resistor for maximum current of 750mA on the current shark as it extends the battery range options and makes the Shark thermal management easier.

There are a lot of pots out there to choose from and I have not suggested any one of them since I have not looked among the many out there to recommend any one in particular. I use digikey or mouser for many of my parts and mouser.

If anyone has a pot they have used and would like to recommend or share it that would be great.

Wayne

 

[wvaltakis2]

Thanks a lot Wayne, order placed.

~Chip

 

[wvaltakis2]

Flickering problem

So I have this driving a string of 5 one watt nichias off a D lithium with the "recomended" digikey 20k pot. The "upper" half of rotation doesn't seem to be doing anything and it flickers pretty bad. Did I get a bad pot or maybe a bad connection? Just looking for some input before I tear into it again.

~Chip

 

[wvaltakis2]

Flickering problem?

Maybe I wired it wrong? Currently I have the center tap going to the large pad and the two outer taps to the small pads...a little help please?

~Chip

 

[dat2zip]

The Shark really works best with multi-cell batteries. That said, your configuration should be OK.

You need to be careful to not let the battery voltage drop below 3V as seen by the converter board. So, even if your battery may be have a partial charge it's possible that the battery sag, wire voltage drops, voltage drop across the switch could make the voltage less by the time it gets to the converter board. When it drops below 3V the converter will not work correctly and possibly flash, blink or do other things. I don't know to what extent or behavior under these conditions.

I believe you have the pot hooked up correctly. I would test with only a fresh cell or with multi-cell to determine where the issue is. If with two cells you have full range control then one cell is not a working configuration and you might want to consider using larger wires and or switch to lower the losses in the wires/switches to see if that will help the one cell configuration.

You can also measure the voltage at the converter board while it's running to see if it's high enough.

Bottom line. If there is any way to up the input voltage would help the shark out a lot.

Make sure the Shark isn't getting hot. If it's getting hot it gets very inefficient.

Wayne

 

[wvaltakis2]

Thanks Wayne,

I should have mentioned that the first thing I tried was boosting the voltage with a second battery, no change. I guess I'll have to take it apart and check hinge out. I'm fairly certain it has more than adequate heatsinking but I'll check the Shark to make sure.

~Chip

 

[dat2zip]

Can you measure the battery current? Just curious on the battery current when you have full power.

I recall modifying the Shark and replacing the sense resistor. Pretty certain that is the one you got. You should not be drawing more than about 1.6A or so from the battery.

Is it possible that you got a 200k pot instead of a 20K pot? That might behave what you describe.

Wayne