Converting Spotlight Power Supply

[stj]

Re: Converting Spotlight Power Supply

in plain language, your going to have to deal with the optics to get the beam angle you want.

[Curious.George]

Re: Converting Spotlight Power Supply

I know its long obsolete tech with plenty of heat dissipated. Speaking about efficiencies, can you guys suggest a modern cree led 50W spotlight at low cost? I've small cree or similar flashlights brighter than this spotlight, but larger cree lamps seems to be on a costlier side.

You're thinking in the wrong terms (units of measurement).

A "50W cree" will dissipate just as much power (heat) as a 50W incandescent.

What you really want is an LED that throws as much LIGHT as the 50W incandescent/halogen -- but at a much lower power dissipation.

And, this is where things get tricky... are you concerned with "total light output" OR light at a specific point in space? (SPOTlight)

[sambul83]

Re: Converting Spotlight Power Supply

I know its long obsolete tech with plenty of heat dissipated. Speaking about efficiencies, can you guys suggest a modern cree led 50W spotlight at low cost? I've small cree or similar flashlights brighter than this spotlight, but larger cree lamps seems to be on a costlier side.

@ stj

Thanks for pointing to this nice recovery charger.

[Curious.George]

Re: Converting Spotlight Power Supply

plastic melts, wires heat up, tracks burn - and most barrel connectors are only rated for a couple of amps.
the ones on laptops are constructed differently - even the plugs are different and more expensive.

Moving to a higher voltage could conceivably only increase the power dissipated in the bulb and not affect the current flowing through conductors (foil and wire). E.g., a 50W 12V bulb would result in the same amount of current flowing as would a 25W 6V bulb.

What's changing is the POWER. And, that translates into heat.

Leave such a lamp on for any length of time and I suspect you'll find the acrylic "lens" turns to mush. Plastic parts in and near the "socket" (I've not examined this particular lamp) could also be compromised.

We ALL know how hot light bulbs get -- having each tried to remove one before letting it cool down, completely!

(Note to OP: don't touch bulb glass -- even while cool -- with your fingertips as the oils from your hand will compromise the bulb. Wear gloves or use a clean tissue/cloth)

[Curious.George]

Re: Converting Spotlight Power Supply

Wouldn't adjusting the resistor value on that board, soldered in sequence now with the diode, and shorting the diode allow to use 12V power adapter instead of 6V?

Think about it... you want to ensure the "bulb" never sees more than 6V (lest you "open" the filament). So, roughly half (6V) of the voltage available (12) would have to disappear across that resistor. In effect, you woul dhave an equivalent light bulb *inside* the lamp operating at the same voltage as the real light bulb (6V) and passing exactly the same amount of current THROUGH it (cuz it is in series with the real bulb). So, you would be dissipating roughly the same amount of power IN that resistor as you are in the real bulb... so far, that seems to be ABOUT 25W.

And what can possibly happen with the jack at 12V instead of 6V - melting is not likely I guess? Laptop 12V power adapters are seemingly all switching converters?

The current through the jack would be the same... instead of ~4A at 6V you would see 4A at 12V (in the case of a 50W replacement bulb).

The bigger issue might be the effects on the "lens" (bulb cover) as the doubling of POWER being dissipated in the lamp increases. Light bulbs are inefficient devices. Most of the power dissipated in them is HEAT, not light. Chances are, the type of plastic chosen wasn't selected for its thermal characteristics BEYOND what the original bulb was intended to produce.

[stj]

Re: Converting Spotlight Power Supply

different chemistry.
if you really want to mess with lead-acid batteries then look at a B6 clone like this:
https://www.banggood.com/IMAX-B6-Min...p-1202402.html

[sambul83]

Re: Converting Spotlight Power Supply

Wouldn't adjusting the resistor value on that board, soldered in sequence now with the diode, and shorting the diode allow to use 12V power adapter instead of 6V? And what can possibly happen with the jack at 12V instead of 6V - melting is not likely I guess? Laptop 12V power adapters are seemingly all switching converters?

I can look at a 12V lamp, but current lamp seems soldered now to the wires in a way hard to get to. I couldn't shake it by hand in its sit after removing the holder, and using pliers on the lamp seems prohibitive. Since you mentioned a "dead" battery, I wonder if I can try recovering the dead lead battery with this smarter Nitecore charger? I know, it doesn't support SLA batteries, but what can happen if I try? Won't provide enough voltage at 7.9V to fully charge, but at least may recover the battery to the initial state, from which it can be charged by the supplied lamp charger? Or the charging cycle for lead batteries is totally different?

[stj]

Re: Converting Spotlight Power Supply

plastic melts, wires heat up, tracks burn - and most barrel connectors are only rated for a couple of amps.
the ones on laptops are constructed differently - even the plugs are different and more expensive.

[eccerr0r]

Re: Converting Spotlight Power Supply

... and then the plastic melts (don't go up in watts....)

[Curious.George]

Re: Converting Spotlight Power Supply

Just confirmed using an old Buffalo router power adapter 5V 2.5A. Both lamps are lit now with diode-resistor combo short and also the 2 jack terminals short. It draws 3.5A current, but initial voltage 5.9V drops to 5V, so the lamp is not so bright.

Insert your ammeter into the circuit to see exactly how much power is being drawn by the lamp (power = volts * amps) at that 5V level. This will give you an idea of how much current is likely to be drawn, eventually, at 6V. It rarely hurts to oversize the power supply!

I guess I need to buy a 6V 4A adapter now.

See above.

Is there a way to use a 12V adapter by modding the board, since I've a few with 2.5-3A rating, so they will heat up a bit at 3.5-4A but still working?

Yes, but it would depend on the actual adapter (i.e., it is likely not practical).

A smarter approach might be to see if you can find a (mechanically equivalent) replacement bulb that is rated at 12V (instead of 6V). I have numerous "oversized" lights and use them so rarely that the (rechargeable) batteries are almost always "dead". So, I've taken to just making sturdy (heavy gauge to reduce IR drops over these longer cables) coiled cords with "DC power plugs" (I have no idea what folks now call "lighters" in cars) so that they can be powered from such an "outlet". I've installed additional "outlets" in various places (under hood; rear of vehicle; etc.) to make it convenient to use these lamps. (I also have 12V "power packs" that I can sling over a shoulder for those times when I need to carry such a lamp with me).

What you will then have to worry about is the amount of heat thrown off by any larger lamp that you choose to fit in its place (e.g., you may end up with a 50W lamp instead of 25W -- watts == heat). I have a few "flashlights" that throw enough light (heat) that you can tell if they are on -- with your eyes closed -- just by holding your hand in the beam!

[eccerr0r]

Re: Converting Spotlight Power Supply

Only if you also add a switching converter.

[sambul83]

Re: Converting Spotlight Power Supply

Just confirmed using an old Buffalo router power adapter 5V 2.5A. Both lamps are lit now with diode-resistor combo short and also the 2 jack terminals short. It draws 3.5A current, but initial voltage 5.9V drops to 5V, so the lamp is not so bright. I guess I need to buy a 6V 4A adapter now. Is there a way to use a 12V adapter by modding the board, since I've a few with 2.5-3A rating, so they will heat up a bit at 3.5-4A but still working?

[budm]

Re: Converting Spotlight Power Supply

A lot of these cheap plug in chargers, in order to prevent damage of the charging circuit of the large lamp load, use a 3-wire switched barrel connector that cuts off the load when it's plugged in. You'll have to defeat that switch.

Yep, you can see that the DC input jack has two terminals used for switching out the battery negative from feeding the circuit when the charger is plugged into the DC jack. I have similar set up my spot lights.

[sambul83]

Re: Converting Spotlight Power Supply

A lot of these cheap plug in chargers, in order to prevent damage of the charging circuit of the large lamp load, use a 3-wire switched barrel connector that cuts off the load when it's plugged in.

Yes, that's why the trick with shorting the resistor-diode combo didn't work by itself, so I short 2 power jack mounts too, as it has 3. Will try with the right adapter now. If still not working, will draw the diagram. I don't remember, if the lamp was ever lit when the power adapter was hooked in and the battery charging.

@ Curious.George

Thanks for the explanation and suggested solution. I'm working on it in free time.

[stj]

Re: Converting Spotlight Power Supply

why dont you just draw a diagram of the wiring and board.

btw, your not powering that lamp with the original charger - it will burn up the windings.

[Curious.George]

Re: Converting Spotlight Power Supply

I'm a little confused, how this PCB normally works? Once connected to a power adapter (the bad one with small transformer ), it starts charging the battery. Once the battery charging current drops near 0, the charging circuit then drops slowly, while the battery (only?) supplies voltage to the lamps?

Think of it as two circuits that coexist:

One is the battery powering the lamp (and the little LEDs?). This consists of the battery, the switch/trigger and the lamp.

The other is the charging circuit. It consists of the external transformer, a diode (to ensure "DC" of the correct polarity flows towards the battery) and a ballast resistor to limit the current into the battery.

The voltage loop around this circuit indicates:

Vtransformer -~0.7V (diode) - Ibattery*Rblue = Vbattery

Rearranging this:

Ibattery * Rblue = Vtransformer - 0.7V - Vbattery

This indicates that the current flowing into the battery ("charging current") is

Ibattery = (Vtransformer - 0.7V - Vbattery) / Rblue

I.e., as the battery voltage climbs, the current flowing into it falls.

Ideally, the battery would eventually charge up to (Vtransformer - 0.7V) -- at which point the Ibattery would fall to 0 and charging would stop.

But, Vtransformer is significantly higher than the battery chemistry will ever allow Vbattery to attain. So, there will always be some Ibattery flowing into the battery. This, eventually, "cooks" the battery because it presents as "heat" inside the battery.

That's why these sorts of charging schemes suck.

So, if I short the diode and resistor combo, what should I do with black and red wires hooked to the (former) battery?

Leave them disconnected (tape the ends if you think they might short out to "something") -- there should be planty of room inside the light with the battery gone!

Is voltage to the lamp supplied only through the battery wires, and not by the diode - resistor combo, even if they are short? Or both sources supply voltage to the lamp, and while charging battery voltage raises, current through the diode to the lamp drops? But if the lamp is also fed by the diode circuit, why would the battery discharge so fast?

You're removing the battery so the only path into the "lamp" is via the external power source. If you leave D1 and Rblue in the circuit, then the amount of power that can reach the lamp will be limited by Rblue. The role of that was to limit the CHARGING CURRENT so we want it out of the way.

If you'd prefer, you could wire the external power connector to the battery connections directly. But, if you trace the foils, I suspect you will discover that my "patch" already does this with less work.

[eccerr0r]

Re: Converting Spotlight Power Supply

A lot of these cheap plug in chargers, in order to prevent damage of the charging circuit of the large lamp load, use a 3-wire switched barrel connector that cuts off the load when it's plugged in. You'll have to defeat that switch.

[sambul83]

Re: Converting Spotlight Power Supply

The rating 25W for for this spotlight lamp I found on the web. Its not seen anywhere on the lamp, so I don't know if its accurate. I'm a little confused, how this PCB normally works? Once connected to a power adapter (the bad one with small transformer ), it starts charging the battery. Once the battery charging current drops near 0, the charging circuit then drops slowly, while the battery (only?) supplies voltage to the lamps? So, if I short the diode and resistor combo, what should I do with black and red wires hooked to the (former) battery?

Is voltage to the lamp supplied only through the battery wires, and not by the diode - resistor combo, even if they are short? Or both sources supply voltage to the lamp, and while charging battery voltage raises, current through the diode to the lamp drops? But if the lamp is also fed by the diode circuit, why would the battery discharge so fast?

P.S. I followed your suggestion, but current through VOM stayed at 0. Then I short 2 terminals as shown on the pic below. Side lamp gets lit, but when switching to the main lamp, it didn't lit. I suspect, the current fed by the original adapter is too low for the main lamp, or the diode get turned into a "blown fuse" for the main lamp as the current raises? Will try to find the right adapter 6V 4A tomorrow and check again. If keeping it short like this and it works, would I need to verify or change anything else? I guess still need to short the diode-resistor line?

[Curious.George]

Re: Converting Spotlight Power Supply

I have another 6V 2A adapter with the same plug size.

It also needs to be of the same polarity (which appear to be center positive, barrel negative) and (somewhat) "regulated" -- not just a "transformer with a bridge".

I just need to rewire the board to hook it directly to the lamps through the existing jack without charging a battery. An suggestions namely on rewire, since I don't won't to spend more on this old spotlight?

It would seem that the adapter's "positive" output (the circuit will also tolerate an AC input) is passed through a diode (DIOD1) and then a ballast resistor (the large blue one) to the batteries positive terminal. The barrel of the adapter is "system ground".

So, to act as a battery eliminator, that ballast resistor needs to be bypassed as it will otherwise represent a higher output impedance for the "power supply" (which means less power available to the lamp).

The diode ALSO needs to be replaced as it is probably just a 1A device and the lamp will want to pull several amps through it -- turning it into a (blown) fuse!

~25W = 6V * 4.16A

Even if you fudge the lamp rating and the battery voltage, you're still well above what a 1A diode would be comfortable passing.

You can verify this BEFORE modifying the PCB: get a VOM and set it to the 10A scale (usually, this means moving the "+" lead to a separate input on the meter designated for 10A measuements). Connect the meter across the diode+resistor combination (anode of diode and "battery end" of the resistor).

Plug in power adapter and you should see that ~4A bypassing those components by flowing through your meter. The lamp should light, etc.

[stj]

Re: Converting Spotlight Power Supply

they are junk, just a poor battery, a tiny transformer to charge it, and a motorbike headlamp.

i only did what i did because the case was nice and it had a big reflector - bigger than this one.
and i had all the crap laying around doing nothing.