Willie Hunt Regulator question

[Phaserburn]

In a WH Regulator setup, where the bulb is being supplied 3.6V and is drawing .5A, can the bulb be replaced with another 3.6V one that draws more current, assuming I use NiMH cells that can easily supply it? This question relates to my other one on BD bulb replacement on the Supernova headlamp in the headlamp forum.

 

[js]

Yes. Change away.

The LVR is a voltage regulator (except during soft-start when it limits current). It will draw whatever it needs from the batteries in order to supply the equivalent of (in your case) 3.6VDC to the lamp.

Keep in mind that the voltage of the batteries under load MUST be above the set-point voltage in order for the LVR to regulate. This is more complicated than it sounds, because the instantaneous current draws from the LVR can be very high, and some batteries will sag considerably during these "ON" pulses. Just make sure you have enough of an overvoltage and that the batteries are more than capable of handling the DC current draw that is needed by the lamp.

 

[PeterB]

I think the current demand is even worse.
Lets assume for simplicity a 3.6V / 0.5A lamp and a 7.2V battery (with 0 internal resistance)
The LVR applies 7.2V pulses and during these pulses the current will be 7.2V/lamp-resistance=7.2V/(3.6V/0.5A)=1A
The duty cycle is 25%, resulting in an average current of 0.25A.
The internal battery losses can be quite high if the battery voltage is much higher than the lamp voltage, therefore the high efficiency numbers can be misleading

 

[js]

PeterB,

There is some capacitance in the LVR which smooths things out. Plus, all batteries have a certain amount of free carriers hanging around which will jump into the fray during high demand. These are most often quickly depleted, but not always, and they are quite significant. In lead-acid batteries particularly so.

Anyway, these are definitely at play at the switching frequencies involved in the LVR.

Plus, for most application the battery voltage is less than twice the equivalent bulb voltage, and can never be more than 2.5 times the bulb voltage for safe operation of the LVR.

So, I don't think that the high efficiency numbers of Willie's LVR are misleading at all.

 

[Phaserburn]

In this case, the BD Supernova is a 4-cell unit, or 4.8V nominal. Am I correct in thinking using 4 NiMH AAs would be sufficient to power the regulator and a higher current bulb? If 4 alk AAs can supply a .5A bulb, wouldn't the NiMH's be ok for higher power?

Finding another bi-pin at 1A or so that fits the Supernova is another story. Any info? At what point (watts?) will a plastic reflector have heat issues?

 

[udaman]

[ QUOTE ]
js said:
Yes. Change away.

The LVR is a voltage regulator (except during soft-start when it limits current). It will draw whatever it needs from the batteries in order to supply the equivalent of (in your case) 3.6VDC to the lamp.

Keep in mind that the voltage of the batteries under load MUST be above the set-point voltage in order for the LVR to regulate. This is more complicated than it sounds, because the instantaneous current draws from the LVR can be very high, and some batteries will sag considerably during these "ON" pulses. Just make sure you have enough of an overvoltage and that the batteries are more than capable of handling the DC current draw that is needed by the lamp.


PeterB,

There is some capacitance in the LVR which smooths things out. Plus, all batteries have a certain amount of free carriers hanging around which will jump into the fray during high demand. These are most often quickly depleted, but not always, and they are quite significant. In lead-acid batteries particularly so.

Anyway, these are definitely at play at the switching frequencies involved in the LVR.

Plus, for most application the battery voltage is less than twice the equivalent bulb voltage, and can never be more than 2.5 times the bulb voltage for safe operation of the LVR.

So, I don't think that the high efficiency numbers of Willie's LVR are misleading at all.

[/ QUOTE ]

Show me the money! Show me the money! Oh sorry, I slipped back in time to another thread on regulation, hehe. Hmm, so is js talking smoke out of his *** again /ubbthreads/images/graemlins/wink.gif, where are the links /ubbthreads/images/graemlins/wink.gif to references that support these statements. Ah hah! I knew it, that prior reference to same voltage or higher was blowing smoke out.... As far as Willie H. regulator systems, AFAIK, they all must fit specific voltage parameters, must be some difficult to determine number above, not equal to the voltage you want regulated to (at least until he comes out with better/more flexible versions), and the voltage of your source must also not be too high above the desired regulated voltage...yikes, isn't that like a high-maintenance spouse or g/f /ubbthreads/images/graemlins/grin.gif.

Oh well, I guess it never hurts to repeat the same information in multiple posts, so before I submit my pictorial reviews of the unregulated & regulated versions of the W.Hunt/Skip L. 8AA-2D adapters later tonight or tomorrow...

If only Willie Hunt had set the voltage to 3.8 or 4v, then you'd have shorter bulb life, but much brighter/whiter/higher outputs from a variety of 3.7v bulbs /ubbthreads/images/graemlins/frown.gif

LInks to Willie stuff:

Low voltage lightbulb regulator circuits

Usenet.rec.climbing-Willie Hunts regulators

Counting Crows-
I been hanginaround this town on the corner
I been bummin' around this old town for way, way,
way, way, way too long

Doh, what the...'free carriers hanging around'??? now would that be the top quark, yes? /ubbthreads/images/graemlins/confused.gif What are the free carriers doing during low demands; drooling over JA? /ubbthreads/images/graemlins/crackup.gif

Most, if not all, consumer AA NiMH are rated for capacity at C/10, so it is not easily to anticipate how much voltage drop there will be under higher loads, but any of the batteries that have been mentioned by Ginseng or me for high-wattage/current draw incandescent uses should work fine for anything Phaseburn is considering...umm except. Well there are some bulbs that might/would work for the 8AA-2D regulated adapter which is a 2x4 parallel/series stack (i.e. 4x1.2v = 4.8v are being regulated down to 3.6v).

Carley's 805 xenon at 3.7v/1.6a will be slightly under-driven/yellow---back ordered for at least 7 weeks, or the 1122 halogen-xenon at 3.5v(except it draws 2.3a which maybe too much for the regulator which has only been stated to go up to 2a...maybe when fivemega receives his 1122 potted order, he will post results to the review thread I'll be starting shortly).

It is difficult to say how much heat a specific plastic reflector can handle. In the M*g, where the reflector is not in actual physical contact with the bulb or it's holder, 10w is about the maximum. I know that in a cheap yellow Energizer 6v lantern light where the bulb is held in position in the reflector itself, a 5.5v/1a halogen bulb will start to melt the base of the reflector if the light is left on continuously for long periods.

Carely 1122 Halogen/xenon 138lm, but at 8watts might melt some plastic reflectors

Carley 805 more efficient using 1.6a, and still might melt plastic at a more yellow color and 5.8watts...but the bulb size is T2.5 so the filament is likely bigger, will it focus to nice tight hotspot?

 

[js]

Oddles,

Are you on a mission to annoy me? Good for you that you have JA as your avatar to smooth things over.

A rechargeable battery works due to an electrochemical reaction. This is a complicated thing to model and understand, and to tell the truth I have not tried to do so yet. But one thing I do know for sure is that all batteries can deliver MORE instantaneous or short-term current than continuous current. You see this all the time on web sites "10 amp continuous, 15-20 amp bursts". etc. You have seen this, right? Or do you need me to provide a link, oddles?

Anyway, this is why a lead-acid car battery can provide an insane number of "cranking amps" for starting a car, but the battery couldn't provide that current for very long. Hence the reason why people try a couple times to start their cars, the let the battery "rest". The "free electrolytics" or whatever the heck they are called, have time to replenish.

Blowing smoke indeed! My point is simply that batteries can provide much more "burst" current than continuous current, and this meshes with the LVR regulation scheme.

As for 2.5 being too narrow a factor for batteries and regulation--SAY WHAT? NiMH batteries, for example, start at 1.4-1.45 volts/cell and fall to .8 volts/cell at end of cycle. That's still not 2.5. Heck it's not even a factor of 2.

I honestly don't know what you're talking about sometime, udaman. You're way out there, or left of center, or SOMETHING. And comming from me, that's saying a lot.

BTW, how come you never responded to my PM. I didn't even get a read receipt. Maybe it got lost.

 

[turbodog]

[ QUOTE ]
Phaserburn said:
In a WH Regulator setup, where the bulb is being supplied 3.6V and is drawing .5A, can the bulb be replaced with another 3.6V one that draws more current, assuming I use NiMH cells that can easily supply it? This question relates to my other one on BD bulb replacement on the Supernova headlamp in the headlamp forum.

[/ QUOTE ]

Yes, it's ok to change up to a bulb that pulls a max of 2 amps. Heat is another issue.

Whenever the wa/ca group buy comes in you might be able to find someone that bought some bulbs and buy some from them. I know I am getting several bulbs in the 3.6v range. 3.6v is right where the willie hunt regulator is, the stinger is, and a pila cell runs.

You *might* try a stinger bulb or a strion bulb.

 

[Phaserburn]

turbo, I have a Strion and Stinger bulb on the way already. The SL TT 3C uses 3.6V/.9A bulbs, and might be a good choice should the others not work out.

 

[PeterB]

Jim,

your arguments are certainly right, but nevertheless I believe that the increased current peaks are the main limit for the overall efficiency.
I would like to use some math to show the problem:
Pbulb= Bulb power (should be constant
Vbulb= Bulb voltage
Vbatt= Battery voltage
Iavg= average bulb current= Pbulb/Vbulb
Q = voltage ratio Vbatt/Vbulb
IPeak= Peak bulb current= Q^2*(Pbulb/Vbatt)

The ohmic losses (in the battery+wiring...) are
Ploss= Ipeak^2*R = Q^4*Pbulb^2/Vbatt^2 *R

For a given battery voltage and bulb power the losses increase with (Vbatt/Vbulb)^4, which means that R has to be minimized carefully for large differences and high current bulbs.

 

[js]

[ QUOTE ]
PeterB said:
Jim,

your arguments are certainly right, but nevertheless I believe that the increased current peaks are the main limit for the overall efficiency.
I would like to use some math to show the problem:
Pbulb= Bulb power (should be constant
Vbulb= Bulb voltage
Vbatt= Battery voltage
Iavg= average bulb current= Pbulb/Vbulb
Q = voltage ratio Vbatt/Vbulb
IPeak= Peak bulb current= Q^2*(Pbulb/Vbatt)

The ohmic losses (in the battery+wiring...) are
Ploss= Ipeak^2*R = Q^4*Pbulb^2/Vbatt^2 *R

For a given battery voltage and bulb power the losses increase with (Vbatt/Vbulb)^4, which means that R has to be minimized carefully for large differences and high current bulbs.

[/ QUOTE ]

I agree. Short runs or heavy gauge is a must. And yes, certainly what you say is correct in that this and similar things must reduce the efficiency somewhat. But still, the LVR is pretty darn efficient nonetheless.

But, to get down to some details, I'm not sure I agree with your equation:

IPeak= Peak bulb current= Q^2*(Pbulb/Vbatt)

How did you arrive at this?

 

[PeLu]

As stated before, you need some capacitor, so the peak current is supllied mostly by that.
And a 1:2.5 range is not that bad, actually more than even needed with alkaline D cells, it was choosen wisely.
The Willie Hunt LVR is still the most efficient regulator for use with incandescent bulbs.
And I cannot see how it could be improved. As it is not a switching regulator it never will do anything else as converting down and it never was intended do do anything else. This is not a lack in flexibility, it is just what it is designed for.
And it also does not really regulate voltage, but it does not matter for the user .-)

Edit: BTW, the reason that several batteries have stated a higher short term discharge current is mainly for thermal reasons.

 

[js]

The LVR is NOT a switching regulator? I'm almost certain that this is patently wrong. It IS a switching regulator, and it does really regulate the effective or RMS voltage of the filament. I know this because I know the method by which to measure the regulation setpoint of the LVR with an oscilloscope, and it involves finding the true RMS voltage of the signal. Also, the Fluke 189 has an AC + DC mode that will measure the voltage of the LVR output.