Note this page...modified old detector to use as 12 disconnect alarm. Wiring,switching and power supply for alarm after power turned off was done using it. However last thing was I blew up old detector and ended up using an off the shelf low voltage alarm. Though now irrelevant to adding 12v disconnect alarm, modifications to the old detector left due to that how wiring was laid out and described.

This page entirely for my own reference...IF adding a system disconnect alarm tied into camper 12v system there is enough residual voltage to power alarm for a second or 2 with no other modifications needed.

Adding 'back' battery disconnect alarm

Replaced the LP detector...

Our original was a CCI Controls #7773.2. No longer made. MTI Industries makes a direct replacement 30-442-P. Original is installed in a cutout on wall so using the MTI al was a CCI Controls #7773.2. No longer made. MTI Industries makes a direct replacement 30-442-P. Original is installed in a cutout on wall so using the MTI that uses same hole, seems like easy decision.

However new detectors do not set off alarm with low voltage or being disconnected. Didn't realize that until installed. Also, from what I gather, new ones have about 10% early failure rate, usually in the middle of the night. So I added a switch for ability to disable LP detector without having to disassemble cabinet to get to it should that event happen. To alert against detector accidentally being switched off adding 'back' an alarm, secondary but I also miss the audible conformation when batteries shut down.

Well vendor talked me out of ordering low voltage alarm I was looking at saying he didn't think it would work for our application. 12v disconnect verses low voltage... on the one hand correct, turning off 12v would trigger alarm but there would be no power for it to sound. He could not say if residual system voltage stored by camper would let alarm sound, (like our old detector did). But because I added a switch before detector it removes system residual voltage to sound anyway.

So I'm going to set up modifying old detector. If I can get it to work, sound after system power removed, then pursue adding alarm unless modifying detector works well enough. Testing old detector indeed powering from 12v power supply, turning off power supply, detector sounds for a second until power drained from supply. Turning off with switch, removing detector from supply, detector only chirps. So need a source of power to allow alarm to sound for a second or so if power cut....

Capacitors! They charge and store power while connected then discharge when power removed, keeping alarm powered, albeit briefly. Would duplicate system drain down....So to verify idea without buying alarm to test Im hacking old detector to use as'n alarm. It has the function, alarm when voltage removed and a very obnoxious speaker. Just need to disable the sensor part removing any potential LP alarm feature (or failure).

    update: you can skip this section or continue FYI but I blew up the detector. It was working awesome-free but last mod shorted it out. All of the wiring, added power source and switching will remain and transfer over to new alarm.

    What makes the unit an LP detector work

    Obviously lot of other stuff but this is main component, ...TGS2610 sensor. Two function, a small heater and the sensor element. I tried just removing unit but power pass thru of the heater needs to be seen by board that its working or it sounds alarm. So cut the 2 legs of the element taking it out of circuit, leaving its heater intact.

    Shown here legs #1&4 cut and isolated. I didn't try, though will if this works, a jumper from pins 2&3, allowing power to pass but removing failure possibility of heater. I suspect more units fail because the heater quits verse element failing. What i don't know if its a measured amount or just any power going thru heater. Once this works (supplying capacitor power) I can afford to play with. If I fry board I can replace with an off the shelf alarm.

    Now for capacitors, ...

    Old computer mother board,. It has 4 16v 1500uF capacitors. Perfect, well free, removed from board

    Assembled as pack, adding diode so this only feeds detector. Also adding a light before 'pack' on the incoming 12v to help with charging capacitors.

    Light bulb just helps with the inrush current on initial charge (detector powering up). Bulb gets bright then all but goes off once capacitors 'charged'. Also, sort of, acts as fuse.

    Initial plan

    As system 12v disconnect alarm but more to alert if switch to LP detector turned off.

    And final, though can defeat power off to LP detector alert, I added another switch. It allows turning off alarm should it fail (more likely) keeping LP detector powered (again generally alarm fail is in the ON mode). Which is why the initial addition of switch in the 1st place. So at dark thirty, alarms going off, I can disable with out tearing into cabinets to get to wiring. Turn off gas go back to sleep-alert. This is what Im doing, not what you should do.

    Testing modified old detector with capacitor pack and it works. Remove power by turning off power supply, units alarms until power drained from supply, remove detectors lead from power source alarm still sounds for about 1 1/2 seconds draining capacitors. Cool.

    Hot glued capacitors inside of old detector. Used acetone wiping any LP reference, labeled just because..

    Installed in camper.'New' alarm is behind paneling. Wired its switch to receive power from lead to LP detector. Behind the paneling muffled alarm to much, ended up cutting a hole for speaker.. Hoping I wouldn't need to add extra hole. But it works.

    Turning off either switch sounds alarm or 12v system turned off sounds alarm. Alarm can be disabled and still have LP detector. Normal active is both switches on. Pretty happy- wasn't sure.

    As I've already added ability to defeat alarm adding the alarm switch, I think I'm going to change its switch to a double throw. So it can be powered by LP detector on, off or direct to 12v system. Logic is for home use/no propane, not short cycling the LP detector and still have audible 12v system alert. If I die because I added a switch- well serve me, thin out and strengthen the gene pool. Not really cause I already have offspring...

    Just switch wiring....

    Replaced the alarms on/off with an on/off/on. Power from LP detector/off/ or direct power from camper. Works well, Decided to remove alarm again, take out its pilot and add about 12" of wire to remotely mount it so I can 'see' when its powered. If alarm sounds you can see at a glance which is turned off. Course I guess just looking at switches would tell...Removed pilot, add 12" lead between board and LED. Tested-cool remote LED

    Getting ready to drill the mount flange of LP detector so the alarms LED would be directly under the new LP detector 'on' pilot. 1st I want to look at the heater, see if I can bypass or remove.

    Looking to see if I can bypass heater circuit. Not liking how intense its glowing...I don't know if its always done that or its getting more power due to element disconnected, either way its unneeded source of failure

      And FAIL
    Setting up on power supply, testing the alarm, rewired LED then I probed the heaters pins to measure how much power going thru and POP!! and smoke. Not sure exactly what I touched but blew out half the circuit components. jeesh...I managed to find most of the components that obviously blew. Robbing old electronic boards for parts, replacing bad stuff, but couldn't get it so much as blink. Its toast.
    Really bummed because it was working, then again the heater kinda bothered me so maybe it was short lived any way. One the other hand proved 'proof of concept'. I hadn't really thought I would use old detector other than to see if I could make it work as an alarm, and if so then getting an alarm. It was just that I got this far and it almost worked. Gonna have that sometimes..

    New alarm is in the mail.

    Starting over.

    Well not exactly, switching, wiring and capacitor will be reused, just replacing my 'custom' alarm with an off the shelf unit

    New alarm is a low voltage detector. Simple small unit, should 'bolt in' in lieu of my cannibalized old detector.

    Issue is mounting, its just a circuit board. Then getting its 'horn' mounted over the hole I cut in paneling. I assume I can flip the piezo so it protrudes other side of board (ordered 2 :). Still have access to pot and terminals.

    Sketched in the frame work behind paneling. Modified detector sat within framework. Cant mount new alarm to paneling. What I came up with. Cut a piece of 1x4 (yellow) to fit within existing 1x2 frame on paneling. Will allow mounting the new alarm to it, then place behind paneling.

    Mounting the alarm and capacitors. Bored a couple of holes to create funnel for sound, hole lines up with hole in paneling. Should address how muted placing behind paneling was but more to place over existing hole.

    Cover 1x4 with aluminum tape, I dunno-electronics on wood...Cut up the old lp detector case, shorten about an inch. The old case will screw to the 1x4 as a cover. Using old circuit board as an insulator. New alarms horn will enter 'funnel'.

    Problem is I need to access wiring terminals and the adjusting pot. With the horn into 1x facing outward they also would be inside funnel.

    Only 2 solder pins hold horn so un-soldered and flipped to other side of board (pins to same holes)

    Horn will enter funnel with the terminals and pot exposed and accessible.

    Cleaned off old detectors board, drilled 1/2" hole for horn, mounted components. Though self supporting, immobilized with hot glue, adding few zip ties

    Assembled. Pretty hacked but very functional

    Added alarm pilot to flange of LP detector

    Though I drilled and installed thru the flange, not interacting/ with the internals of detector, Im sure warranty null & void.

    Slipped assembly into framework-not that this shows much. Single screw at angle thru top frame holds in place

    Mounted and functioning. Really odd is to the naked eye the LED colors are reversed to what the camera shows?
    Have LP detector, switch to disable should it fail, audible alarm if/when switch power to LP detector turned off, switch to power alarm by detector power, disable alarm or use alarm without detector. Visual leds for both.
    Normal use both switches on. In storage when camper not being used, LP detector would be switched off, alarm left on, so going in out of camper still have audible alert power on/off without short cycling detector.

    And lastly, paint tops of switches

    as secondary reminder of switches position. Camper in use should not see red...

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