AMC 7135's

[Packhorse]

Is there a practical limit to the number of AMC 7135 chips you can use?


I want to build a SST-90 based light running off a 8 x 18650 li Ion 3.7v battery pack.

I have made a few assumptions that may prove incorrect but we shell see.

On a fully charged battery the voltage will probably sag to at least 4 volt under load.
If I run the SST-90 at 7 amps (20 AMC's) the VF may be 3.6-3.7, So I need a voltage drop of 0.3-0.4volt. 0.4x7 is 2.8 watts that needs to be dissipated. Worst case I guess it could be double that.

Anyone done this before?

 

[tx101]

I asked a similar question a while ago here

http://www.candlepowerforums.com/vb/showthread.php?t=244079

In post #8 Darkzero states that he has tried some 8 x7135 and 10x7135
with 4 x NiMh cells. The 7135s get hot so who knows what will happen with
20

 

[Packhorse]

Thanks. I will running my at a lower voltage so I dont see the heat as a big issue ( I may be wrong).

 

[darkzero]

Thanks. I will running my at a lower voltage so I dont see the heat as a big issue ( I may be wrong).

When I was playing around with these, in my experiences, using more than 8 7315s with either one li-ion or three NiMhs, voltage drop under load was too much & the desired current couldn't be reached. With 4 NiMhs the current was delivered but the ICs got very hot very quick. I never tested to see what that sweet spot was since it would matter anyway as I wouldn't be able to find a suitable battery to deliver the required voltage under load. This was before IMRs hit the market which is a different story now.

 

[Packhorse]

Thanks for your input DZ.

I guess when you get to that point direct drive is a good option.

But for me the size of the battery pack is not really a concern.
As it is I can go up to 14 18650 cells. But 8 is what I am aiming for.
This will give ma about 0.35C discharge.


This is the project here. Skip to post 83 for the actual project.