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Dacor UL750 LED conversion - DIY
*****Warning: As the title of this forum states, the following is DIY. Try this at YOUR OWN RISK**** (ie. NEVER A BAD IDEA TO CARRY A SPARE LIGHT (or 2) WHEN DIVING)
Rather than dole out a couple hundred bucks for a new high-output/super-bright LED underwater light i decided to try and replace the existing halogen GE 7550 bulb in my Dacor UL 750 dive light. The stock bulb is a 8w 6-volt Par 36 halogen bulb. Retails for around $10 but is prone to breakage every time you open the light and average life expectancy (approx. 50hrs according to GE). I have no idea what lumens a GE 7550 8w halogen bulb delivers. If I remember correctly i would get anywhere from 18-24 hrs of burn time with a single alkaline 6-volt lantern battery. The battery this light is designed to use.
GE 7550 6-volt halogen screw terminal;
Operating Voltage - 6 volts
Watts - 8w
Amperage - 8w / 6volts = 1.33amps
Life expectancy - approx. 50hrs
LED replacement bulb
If you do some searching online there are loads of Par 36 bulbs out there but not many choices when it comes to ultra-bright LED (also known as WhiteLight) in DC voltage...especially 6-volt. This project uses the Grote 12v 'Trilliant' 36 bulb. Recently purchased here in Toronto, Ontario for $120 on sale at a local auto-parts store. Comes in a standard 'Tractor-beam' or 'Wide-angle' projection. I bought the 'Tractor-beam' version (Grote part #63821-5) Grote makes all kinds of automotive/tractor/utility vehicle stuff so i figured they are a reliable source for quality LED products. Not all LED lights are equal. These are the specs for the 'Trilliant' 36 bulb;
Diameter - 4.39" (111.63mm)
Depth - 1.42" (49.29mm)
Operating Voltage - 10 to 30 volts (this is important as you don't want the LED to shut off during normal battery operation - ie. inevitable drop in voltage)
Amperage - 1.4A at 12 volts / 1.44A at 12 volts
2 qty. 4 C-cell battery holders with solder tabs
3 or 4 packs of quick connectors (depending if you want to keep your old setup/bulb & 6-volt power source)
Now, of course you're probably thinking...12-volt? how do you run that with a 6-volt lantern battery? Good question. In fact, a lot of 6-volt batteries are simply 4 individual 1.5-volt batteries packed into the square metal shell. Often they are 'F-cells'. Not readily available in stores or online (I suppose if you're a hard-core battery person you can find these no problem) It's relatively straightforward building your own battery 'pack' as long as the combination of cells totals 12-volts
8 x 1.5-volt AA
8 x 1.5-volt C
8 x 1.5-volt D (doubt i could fit 8 of these in this lamp shell)
I chose to go with 8 C-cell batteries. This battery is relatively cheap and easy to find in various stores (hardware, pharmacy, grocery etc.)
This DIY project could very easily use rechargeable C cells but i don't own any (yet). I think alkaline has longer amp hours than rechargeables though (in general at least)
I built the battery holder using a combination of 2, 4 C-cell holders as you'll see below. Fortunately for me they came with plastic snaps on their backs so i could simply 'click' them together and voila, instant 8-cell cartridge. Each holder has battery solder 'tabs' so it was quite easy to solder the 2 in series (also commonly referred to as 'daisy-chain') to get the required 12-volts.
The Grote LED bulb is designed as a direct replacement for normal 12 volt Par 36 bulbs. Used a lot on tractors apparently?
Therefore it 'should' fit the Dacor UL750 no problem. It does, but make sure you line up the bump on the back of the bulb with the correct location on the Dacor UL750 housing (see picture below)
I'm no expert but I'm pretty sure that flashlight performance is largely related to the current draw (amps) of the bulb(s) AND the capacity of the battery(ies) supplying the power.
I have minimal knowledge of battery current discharge 'curves' so i'll leave the exact math up to you. Here's a brief (rough guess) overview of what i would expect from this LED bulb;
17 watts / 12 volts = 1.4amps (matches manufacturers specs)
A typical alkaline C battery can deliver up to 8000mAh (8 amps for 1 hour, 4 amps for 2 hours ...you get the idea)
8 C batteries x 8amps each = 64amps (In reality probably less but again, these are ROUGH calcs)
64amps / 1.4amps (draw) = 45hrs
Therefore this LED bulb in theory could operate for up to 45hrs on 8 C batteries (Alkaline). Now, i know what you're thinking...45hrs, no way.
I have yet to do an actual test using C batteries however i did build a 8 AA battery pack as well for fun. Installed it, turned on the light and walked away.
After checking every 30 minutes or so i found the light stayed lit for just under 12hrs.
NOTE: The intensity decreased significantly after 2 hours but levelled off for the remaining 10.
I don't think AA can maintain the 12volt output for very long but i have to admit i was surprised how long the light stayed on. Most likely something to do with the electronics of the LED driver/board? maybe someone more knowledgeable can shed some 'light' on this topic
A picture is worth a thousand words, so here you go;
(Experience is worth a thousand pictures)
Thanks for the info. I will definately use your battery pack idea. I was wondering how I would go about getting 12volts.
I've been searching for bulbs that are way less than $120.00. Whelen make aircraft landing and taxi lights that are still in the 180 -200 price range, which to me, defeats the purpose of a DIY modification to this light.
Have you tried it underwater yet? What did you think of 800lm? Nice isn't it?
Thanks for sharing. I may post a link to this on NWDIVECLUB.com when I ask again about replacement leds.
You're right about the cost. I recently bought my Dorcy (shown above. paid approx. $60) as a replacement backup light and I couldn't believe how bright the new ultra-bright LED flashlights are these days! I've seen all kinds of LED flashlights but only the ones with what I would call regular tubular LED bulbs.
The Dorcy & the Grote LED's look almost flat/square shape. They are so bright it hurts the eyes to look at them directly. No comparison to the aforementioned bulbs or halogen for that matter.
I looked at the Whelen bulbs too but couldn't source them under $200 here. I bought the Grote bulb on sale and at the time i asked the fellow behind the counter what the reg. price is... he said $277!! ouch! I don't think they sell many for that. I definitely recommend sourcing it online or through discount auto part dealer if you can...shop around whatever you do.
At this moment i'm literally packing my gear for a trip to Cozumel (leave tomorrow am). I'm hoping my bro-in-law will be in for a nite dive (or 2!)
either way I'll try it out in the pool when we arrive. will try to post some photos of my in-water tests
By the way, this lamp is now ridiculously bright...seriously. I can't believe the difference, there really is NO comparison.
In fact, after some indoor testing i've noticed 2 or 3 yellowish rings (very subtle) within the beam.
I can only guess at this point that it's the old Dacor plastic lens cover that has discoloured over the years and the brilliant/stark whiteness of the LED makes it noticeable...did that make sense?
don't think it will matter much but may show up in photos? something to think about.
I remember a buddy from years ago that bought a pistol-grip 6-volt light (US Divers i think?)
It had a perfectly clear lens cover and focused the light more forward than the Dacor...wish i could get my hands on one of those!
Feel free to PM if you have any questions. I'm not online that often but will check back occasionally
PS. It was your post back in the fall that gave me the idea to try this. Thanks to you!!
Thanks for your very informative writeup. I'm thinking that a battery pack made up of 4 or 8 18650 Li-ion rechargeable batteries at 3.7V 3800mAh each would work well. Four of the larger 26650 Li-ion rechargeable batteries at 3.7V 4800mAh would work as well.
Should be an improvement matching LED technology with the current battery advances.
In my Dacor UL750 light I substituted a 4 D-cell battery pack for the lantern battery years ago. This way rechargeable D size batteries can be used. I have never seen a rechargeable 6V lantern battery. I got the battery holder from Canadian Tire in Toronto. I had to add some lead as ballast in the bottom drawer of the battery holder to get the light to neutral buoyancy. I used several tire balancing weights for this.