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Where are my volts going? trouble with Dorcy Jr. host

Zinsii

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I recently built a laser with a PHR diode running at 125mA, in a Dorcy Jr. host. I had a whole bunch of problems with it (as evidenced here: http://laserpointerforums.com/f38/help-w-broken-phr-pointer-42442.html) but I think i've figured out that the driver isnt getting enough voltage even though the battery is fully charged. Using my DMM, I tested the potential difference of the battery... 2.95 volts, plenty charged. Then, I put it into the bottom half of my Dorcy Jr. host, clicked it on, and measured the potential from the middle hole (that the spring goes into) to the threaded part on the outside which screws into the head... I got 2.32 V. I'm pretty sure that this is why the laser didnt work, because the flexdrive was only getting 2.32V off a full battery.

Now my question is... where did my .63V go? Why am I experiencing such a loss, when I see no corrosion or dirt or anything anywhere? Has anyone else experienced a similar problem?

Thank you
 



cust11

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There will be some power loss from travel. There will also be some loss through the switch. If the battery is weak it could easily drop from 2.9 to 2.3(below flexdrive threshold) simply by turning it on. That is why everyone uses Li-ion batteries. They handle current drain much better than the NiMH non-rechargeable counterparts. I had 2 1.7v e2 lithium batteries in my PHR. Both measured 1.62v but once connected to the battery holder they had a series voltage of 2.8-2.9v. I guess what I am trying to say is stay away from low mAh NiMH batteries and go with some stronger (3.6,3.7v) lith-ion batteries.

14500 = AA
10440 = AAA
15266 = CR2 (approx~)

Those are all 3.7v batteries.

-Mike
 

potatorage

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There will be some power loss from travel. There will also be some loss through the switch. If the battery is weak it could easily drop from 2.9 to 2.3(below flexdrive threshold) simply by turning it on. That is why everyone uses Li-ion batteries. They handle current drain much better than the NiMH non-rechargeable counterparts. I had 2 1.7v e2 lithium batteries in my PHR. Both measured 1.62v but once connected to the battery holder they had a series voltage of 2.8-2.9v. I guess what I am trying to say is stay away from low mAh NiMH batteries and go with some stronger (3.6,3.7v) lith-ion batteries.

14500 = AA
10440 = AAA
15266 = CR2 (approx~)

Those are all 3.7v batteries.

-Mike
He's using a CR123-- a primary one
The voltage loss can be due to bad connections,etc or simply because the battery is weak. Batteries will show less voltage under load than they will open circuit
 

cust11

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He's using a CR123-- a primary one
The voltage loss can be due to bad connections,etc or simply because the battery is weak. Batteries will show less voltage under load than they will open circuit


You got my point across in like 300 less words :shhh:. At least it is a general consensus.

-Mike
 

Zinsii

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He's using a CR123-- a primary one
The voltage loss can be due to bad connections,etc or simply because the battery is weak. Batteries will show less voltage under load than they will open circuit

Yes, I bought some rechargeables at radioshack today. it measures 3.38v, but goes down (seemingly impossibly) to 2.18v when in the host. I'm measuring the potential without load, would that make a difference? these drops seem extremely high, and wont let my flexdrive function
 

dr-ebert

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A primary CR123 with less than ~2.6V under load is dead, plain and simple. Measuring the voltage without load is pretty meaningless. If it shows less than ~2.9V under no-load conditions, I'd chuck it as well without further ado.
 
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Zinsii

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A primary CR123 with less than ~2.6V under load is dead, plain and simple. Measuring the voltage without load is pretty meaningless. If it shows less than ~2.9V under no-load conditions, I'd chuck it as well without further ado.

The problem is, I'm not running any of these tests with load, I'm simply taking measurements with a DMM straight from the battery, then straight from the case with the battery inside and the power turned on. I dont have anything else hooked up to it, and I'm still losing that much, im curious if anyone has any suggestions as to why I get such a low reading.

Until I can figure out what's going on, this host seems worthless
 

dr-ebert

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Ah so. First, make sure that the contact points where you put your probes are clean. The threaded part may be anodized, try sanding it a bit and retry. Make sure you use a fresh battery for that.

Failing that, I'd consider a (reverse-voltage protection?) diode somewhere in the circuit. I've read some post a long time ago, where a current-limiting resistor was hidden under the epoxy holding the switch in place, not quite the same issue but still... Try to take the host apart as far as it'll go to find out where exactly the voltage is lost.
 

CRFultz

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The piece that is pressed into the positive end of the barrel has a circuit board beneath it. That is the original driver for the LED. Did you modify it.
 

Zinsii

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The piece that is pressed into the positive end of the barrel has a circuit board beneath it. That is the original driver for the LED. Did you modify it.

maybe it has something to do with this. I havnt touched it though.
I'm measuring 2.93V (down from the battery's 2.98V today) from the positive contact inside the dorcy to the negative contact of the battery with the bottom of the host removed. (I get my full 2.98V when I put the battery on the bottom spring, click the power on, then measure from the inner rim of the bottom to the positive contact on the battery)

the only measurement I cant get is from the positive battery to the negative contact on top of the bottom half, I might be able to rig up something with wires later but I have to go at the moment.

do you know how I can get to that original driver? thanks
 
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CRFultz

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I remove the whole assy. and use a enclosed module that makes contact with the positive end of the battery. I remove them by placing a round wooden dowel into the battery compartment and using it as a punch, I then "punch out" the driver and pill holder. If i remember, I had used a small drill and drilled a small hole into the very center of the positive contact and soldered a solid wire that would stick up to the height of the hole on the black plastic shield in such to make a good contact with the spring.
This is discussed quite a few times on other posts so you might want to check them before proceeding.
I still make Dorcy's but the heatsink is sealed with the drive inside and a circuit board cap makes the positive contact with the battery. I don't like springs pushing on a fragile little drive. Here is a simular setup. I believe these were for a Aurora host, but the module setup is approximately the same for the dorcy.

DSC01750.jpg

DSC01744.jpg


Good luck

Chuck
 




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