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Changing input voltage on flex drive?

drjava

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If a flex drive is adjusted to a fixed current output (900mA) at 5 volts input, then if the input voltage is increased will the current remain stable? If the input voltage is increased, will the driver get hotter?

I have a DIY blue laser running off a wall wart at 5 v but I'm thinking of making it portable with a 7.2 volt high capacity LiPo airplane battery, but I don't want to cook the diode or the driver.

I also don't want to disconnect the diode to experiment with the dummy load if someone already knows the behavior of flex drives.

Thanks
 

DTR

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The flexdrive is a constant current driver with a max input of 5.5V and like a 2.8V minimum. The current is adjustable by the pot. If you set it to 1A with a 4.2V power source it will still be 1A @ 3.2V input or 1A @ 5V input;)
 

drjava

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Thanks. Especially since you sold me the driver :yh:

I did try to drive it with a 3.6 volt UltraFire ICR123A800mAh but is didn't seem to have enough current. I'll probably need higher capacity ones, or maybe C or D cells.

On the home made linear drivers, the heat on the regulator chip went way up as the input voltage went up. Is that also true of the flex type drivers? Or since they are switched are they immune from this problem?
 

DTR

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With linear drivers the extra voltage is dropped as heat. With a boost/buck driver like the flex it would not heat up any more with 5V compared to 4.2V but from what I have seen it does run a little hotter as the voltage is decreased. I am not sure why. It could be because it is drawing more current or that boosting creates heat. I am not sure. Maybe one of the electronics guys could put their two cents in.

On yours it is possible the battery can not provide enough current. Have you tried different cells? What was the current it is set to on the flex?
 
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drjava

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The flex was set up by you at 900mA. I have to admit it makes a very nice and impressive Blue Laser with the diode I also bought from you.

I have a Laserbee on order and I'll see what it is putting out with its glass lens when it arrives. I'm guessing around 700 to 800mW. I own very high current RC airplane LiPo batteries (from another hobby), but you've reminded me that even the 2 cell ones are way over spec for input voltage. Too bad since I already own them, and the associated rapid chargers. Some of them can supply up to 500 watts and are 2100mAh so it would have been nice to give them a new use powering lasers. The 3 cell ones are 11.1 volts, way too high for the flex. Are there "buck" drivers that could use these batteries to drive a blue diode at about 1 amp?
 

Kevlar

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Could he put 2-3 high amp handling rectifier diodes (1NXXXX) in series between the battery negative and driver negative to drop to voltage of the batteries before it gets to the driver?

Im not expert in electronics but it sounded good in theory to me. :thinking:
 

drjava

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Even if that would drop the voltage, would it be bleeding the power off as heatf in the diodes? If so it's not too attractive to me. Almost defeats the pupose of having a very high energy density battery if your're going to use up energy in heat. There's probably some switched power supplies that can "buck" the voltage without loosing power, but unless it's something I can buy for not too much I'll just give up on those batteries for lasers. I don't know if voltage dropping diodes are electrically different then adding resistance in series to drop the voltage. The resistors would certainly just make heat.
 

drjava

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In the laser hosts that take two lithium batteries, wouldn't the voltage be somewhere around 2 times 3.6 or 7.2 volts? What kind of drivers do they use?
 

Kevlar

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Like dtr said, linear drivers. The one he recommend from jib are very good.

There are several members who are very knowledgeable in electronics, hopefully they can chime in.
 
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LaZeRz

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Hosts that take 2x lithium batteries take Linear drivers.

Boost drivers dont need more then 4.2 volts because the convert current into voltage.

For example: A linear 1.3amp driver will take 1.3 amps because it isnt using extra current to produce more voltage. On the other hand, A boost will take less voltage but at 1.3amps it can take up to 2amps of current to convert it into extra voltage.

My hotlight build in my signature uses one of Jib's linear drivers at 429ma

I also have another hotlight with a 1.3-1.6amp linear from Jib
 
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LaZeRz

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You could also do this:



If you run your cells in parallel (connecting positive to positive and negative to negative) with a spacer inbetween you could double your run times and half your voltage.

For example, if you had two 900mah cells at 3.6 volts you would end up with (in theory)

1 cell with a 1800mah capacity at 3.6volts
 

Tonga

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Unless I missed something your 3.6v you mentioned above should easily work. I have a micro flex V5 set at about 1475mA in a host that uses the AW IRC123 750mAh and it fires around 1400mW just fine.
 




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