ELIMINATE 2 'D' CELL BATTERIES

[CJ WORTH]

Hello All: CJ Worth here with a question re: tankless water heater; LP Gas heated - 18L tankless - USA 120V household current - 2 'D" cells for igniter - water pressure automatically excites igniter -

(step-by-step / part for part)(where it goes, etc) --- I am a Kia auto expert not an electrician } What I need is a diagram and exactly what to buy and how to build a compete battery eliminator. I tried a good quality 3v-4 1/2v-6v-7 1/2v-9v 12v (switchable) with dummy D cells all checked out according to multimeter/ohms readings however, it will not fire(ignite) gas. So, whatever I did was somehow not correct.
Can anyone out there give me a simple diagram and a layman's instruction on how to build one? In the alternative, can I purchase a "drop-in" eliminator? is yes, brand? model? where to buy? cost? THANK YOU, CJ WORTH
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[dick_freebird]

An igniter being a spark generator, probably wants a high
(but brief) primary current and then snap it off to get flyback
voltage across a spark gap.

That means probably a relatively high current for the
duration of the coil dwell. Those "battery eliminator"
products may not match the short circuit current of a
D cell, if they're meant to power a radio or other low
drain electronics.

I'd start with measuring a D battery's load line, and
comparing to the "eliminator" specs - particularly max
output current, but check the basis (they may spec
current @ 1.5V, which may not be how the igniter really
operates - may just be D cells, coil and relay, and the
current can go a lot higher if you let the voltage drop
some more.

If you have a 'scope you could put across fresh working
D batteries in the water heater, and record the ignition
event, that might help you decide what the power source
attributes need to be.

But roughly speaking I'd check around for a 3V, >2A
DC-DC (or AC-DC) converter - or a 3VDC "wall wart"
and a really fat capacitor (I believe they sell supercapacitors
in that range, which likely would do the job; you could
use a higher voltage wall wart with a resistor divider to
charge to exactly 3V if that is easier to come by.

 

[crutschow]

You could try a super-capacitor (1 Farad or more) as dick suggested, with the power supply you have.