18 volt timer

[stinkingdog101]

I am using two 18 volt cordless drill batteries to power a 12 volt trolling motor. It is a low budget toy that I am assembling out of PVC pipe . I want to be able to use a timer on this motor that will not exceed 5 minute run time. As you can see I have a disparity between the voltages > although the motor seems quite happy at 18 volts. I saw a timer on Ebay that is a DEI 528T adjustable 12 volt pulse timer but the timing only runs up to 90 seconds. This seems idea with the exception of the run time. I need at least 1 to 5 minutes adjustable. ALso the voltage is wrong. Any ideas as to how I ca get this home built project off the ground would certainly be appreciated.

 

[shrtrnd]

My only input, would be that over time, you may cook your 12V motor, running it at 18V. I think you should drop your voltage, then work on your timer. Frankly, I'd be looking at an already build timer, mechanical if possible (used a lot in sauna/spa applications. (Works basically like an egg or cooking single-turn wind-up timer, with elec contacts.)
All Electronics Corp in California frequently has cheap timers like this. They buy closeouts from companies who end production runs, and then sell-off their excess inventory. If you go to them on the net, and get on their mailing list, you get their most recent stock in a printed catalog, once a month (besides what you see on their website). Good luck on the project.

 

[NickS]

Don't forget scavenging. You can find high current wind up timers in toaster ovens too so maybe a trip to a local second hand store could yield the part. As for the voltage drop you want to use a buck converter but for us to be much help we need to know what kind of power the motor requires.