Converting Spotlight Power Supply

[sambul83]

I've an old Canadian Tire 37-9452 Halogen Spotlight, which seems to have 2mln candle H3 6v 25W halogen lamp, powered by lead battery SD620 6v 2Ah (cycle 7.25-7.45, standby 6.8-6.9 Yuyao SanDing Electric Ltd, size 3x1.85x1.5 inch), which is charged by the power adapter TL-9B 9V 300mA.

The battery is now dead, and I can't find replacement of the same size that would fit inside the Spotlight. Can you guys suggest & link a suitable battery model? May be using Li-Ion battery will be the best choice, but which one and how to charge it regularly without the Spotlight disassembly, as the internal charger is very basic and likely won't do it?

Alternatively, I'd use it without a battery, by powering directly from a 6V 2A power adapter, connected to the same female connector on the Spotlight. The question is, how to modify the PCB schematics to preserve all switches functionality (side/main lamp switch, handle lamp On/Off, red power led), but power the lamp directly? Current PCB layout only seems to charge the battery, which in turn powers the lamp if there is any remaining charge in the battery.

Interesting is, the battery is 6v 2A, but the power adapter used is 9V 300mA, and in fact its idle voltage is 18V DC as measured by a multimeter. Why is that?

[sam_sam_sam]

Re: Converting Spotlight Power Supply

Here is a thought

Use a one to three watt LED module where the front lamp is there now and use 18650 or 26650 batteries

[eccerr0r]

Re: Converting Spotlight Power Supply

Powersonic PS-621 SLA should be a fit. It seems to be fairly readily available. Remember it's a 6V 2Ah battery pack. That 'h' is important.

Power adapters for lead acid charging tend to be really crappy resistive drop diode halfwave rectifier. Except if you leave it charging, yes it will kill the battery eventually. However they work fairly well for a while and is very cheap...

I don't think you can use that wall wart to light the lamp. The wall wart cannot supply enough power by itself - it needs the battery as a "capacitor" - you have to get a much beefier power supply to light the bulb. Even a 6V 2A power adapter is too weak, you need a 4A power adapter.

[sambul83]

Re: Converting Spotlight Power Supply

Thanks for the battery hint, though its too costly in Canada for the task, like CAD45 shipped. And if I use 3W led module, I'd need to replace the internal battery charger with some different board? There might be a problem with holding the 3W module in place or cooling it well.

I prefer to power the front and side lamps directly from a 6V 2A power adapter I have, and don't use any battery. Would that be the right spec adapter, and how should I rewire the existing board? I can post more pics if the board layout is unclear.

[stj]

Re: Converting Spotlight Power Supply

i have seen those with split open batteries, the charger is shit and kills the pack.

[CapLeaker]

Re: Converting Spotlight Power Supply

that charger killed that SLA battery. They just gave you the cheapest transformer based dumb charger there is. Look at the dimensions of that battery. Maybe a regular 6V 4Ah will fit? I think it is the same length and width, but I can't see the depth. And don't use that charger anymore, or you will kill the next battery too, because the charger does not stop charging the battery, hence a dumb charger.

If you want, just wire a 6V PSU to the terminal where the battery was. You saw the 18V on that charger, because it wasn't loaded. As you load it more and more, the V will drop.

[sambul83]

Re: Converting Spotlight Power Supply

The 6V 4Ah battery won't fit for sure, its longer and somewhat bigger. I'm looking for "no battery" solution now.

I wanted to reuse the existing jack that is firmly mounted in the plastic case and is preferred to a 2nd standalone jack wired to battery terminals. I just need to figure out how to disable the charging circuit without affecting other functionality like switching btw front and side lamps, red power led, and a lamp handle power switch. Its likely a very simple rewire, I'm just not good enough in PCB schematics to figure it out, but can solder easily if someone suggests required changes.

I wonder if I can simply short the former battery wires to the existing power adapter jack contacts on the board? Since the 6V 2A power adapter will provide 6V, the charging circuit may stop charging the "battery" thinking its fully charged, and the lamps will be powered by the adapter via the existing jack, with all switches working. How does that sound?

[kaboom]

Re: Converting Spotlight Power Supply

i have seen those with split open batteries, the charger is shit and kills the pack.

Yes, 9v under load! 18V unloaded/9 under load suggests a 12v transformer which is severely undersized= cheep junk.
Even under load, this one's 3v too high!

A 7806 with a 1N4004 elevating the common leg (setpoint 6.7v) with a schottkey in series to batt + will do. The max charge voltage will be ~6.3V. Another 4004 in the common leg will raise standby voltage to ~7v; one schottkey and one 4004 will give ~6.7v.

The buck-converter equivalent is an option for reduced dissipation.

[sambul83]

Re: Converting Spotlight Power Supply

Is your above advice related to improving the charger? But I don't have a reasonably priced battery for it. Can you suggest, how to rewire the board to power the lamps straight from the power adapter?

[kaboom]

Re: Converting Spotlight Power Supply

Is your above advice related to improving the charger? But I don't have a reasonably priced battery for it. Can you suggest, how to rewire the board to power the lamps straight from the power adapter?

You can't do this with the adapter you have now. It's not even remotely adequate.

[stj]

Re: Converting Spotlight Power Supply

check ali-express for the battery, but be warned - most of these lamps cost less than a decent battery.
also the average life of a sealed gel-cell is 2-3years only.
(with correct charging)

[stj]

Re: Converting Spotlight Power Supply

i actually adapted one of these many years ago to use a compact flourescent lamp in the front, driven by the guts of an amergency escape sign in the back.
(charger/invertor + "C" nicad pack.)

[sambul83]

Re: Converting Spotlight Power Supply

@ kaboom

I have another 6V 2A adapter with the same plug size. I just need to rewire the board to hook it directly to the lamps through the existing jack without charging a battery. No such batteries on Aliexpress either, and they won't hold the charge for a long anyway, so the lamp was bright only for a short time on a battery, and then faded. An suggestions namely on rewire, since I don't won't to spend more on this old spotlight?

[eccerr0r]

Re: Converting Spotlight Power Supply

You need a 6V PSU that can supply 4 amperes. Else you will need a battery that has low enough impedance to supply that 4 amperes (which that 6V 2Ah battery can do.)

[eccerr0r]

Re: Converting Spotlight Power Supply

You know... that 2Ah battery and that 25W halogen lamp, I would only expect it to last maybe 20 minutes anyway, and that's with a new battery...

... just to reset people's expectations...

[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.

[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.

[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?

[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.

[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.