12v to 3v conversion

Thanks again for detailed research and advice. I look forward to putting it all together. I may take a few months to get around to it, but I will post pictures when it is done. James

Oldspark, It worked just as you suggested. I soldered the connections and it is working fine. I will connect the other 5 timers and a solar panel and let it run all summer. Thanks a million, James [/IMG]

James - thank you 2-million! Great to get your update and a working pic (which already looks as permanently installed as many of my projects LOL). I see you went with the eBay 121171591143 LM2596 DC-DC Step Down Module. I'll consider that for my future buys - its connectors are a nice addition and it has the common reverse polarity and overload protection and multiturn pot. Even tho your timers might do with far sloppier voltage regulation using mere resistors or zeners, IMO the LM2596's fourfold power consumption difference from 12V is a massive advantage. IE a 12V battery will last 4x longer, or can be 4x smaller etc. Or 2x if using a 6V battery. Look for lot's of five etc deals for that or similar converters. Not that I'd normally risk big bucks on an unsampled bulk buy but such converters are mature technology and I have yet to find any duds. (Maybe 3-4 different buys of lots of 5; all tested tho only a few used in practice.) And I always buy extra for convenience or spares - especially if postage costs are high (and units cheap) - tho mine are almost always ex-China with free postage... dang! - can't use unit versus postage cost to help determine optimum quantity buy.     Incidentally, you'll probably find that after setting the trimpot and attaching the connectors you can seal the module - eg, coat with some conformal coating - except perhaps if running nearer to 2A output without heatsinking. I'll often spray 2 coats of PCB Lacquer before dangling my things in engine bays etc. My 1.2MHz dc-dc converter worked fine like that - I suspect its temporary outage after a high pressure wash had more to do with its distant connectors that may have water-shorted. My point being that you can probably stick the LM2596 modules to the back of the timers etc rather than the trouble of a housing etc. Otherwise co-locate the modules in a box near the battery or solar regulator etc. Which location method depends on situation & preference. EG - dc-dc converters are usually at the load end for long transmission distances to compensate for voltage drops, or where mere end replacement does both converter & timer. Otherwise central colocation of modules may be the more desirable.    Anyhow, best wishes. I hope the modules prove reliable (I'm sure they will). Lifetime cost $aving$ could be an interesting followup tho you said ~monthly replacement of 2 AA batts so using my calcs... two Aldi 25c AA cells => 50c/month so after 12 months you're ahead excluding solar & 12V batt costs. Then there's the maintenance free and "set & forget" aspect...

First, due to low water pressure, we only open one timer at a time. The module is rated for 10A. I planned on using one module and running the timers in parallel unless that is a bad idea. If that presents a problem I can always add 4 more modules. I plan to buy spares anyway. I prefer to place them near the battery and solar panel in a protective case. My only concern is condensation if the case sweats. My design takes into account the line drop over the longest run of 30 feet.

By module do you mean the dc-dc converter? (Because isn't that only rated for 2A else 3A with heatsinking etc?) If you mean something else then fine. (eg solar module etc) Timers in parallel should be fine. IE - I think your timer/valves were all low current and one dc-dc conv may handle all or more than one. (Unless that's the 10A module you referred to in which case it's a peak load and might still be ok...?) Plus the dc-dc conv is supposedly self protecting and should shutdown in case of overcurrent (rather than cause a brownout situation that can damage loads). If so, a power cycle resets the dc-dc conv. [ If it does limit current but continue to supply at a lower voltage like analog/linear voltage regulators do, then beware - the timers/valves may not like it! ] One concern might be simultaneous power-on or switching of valves resulting in current surges but they are likely to be short and handled by the dc-dc conv. And maybe capacitor(s)... But see if you have behavior problems. I'm thinking maybe a small cap to act as a filter against valve transients, and maybe a larger cap for current-surge ride-thru, but that/they might have issues (but probably not).      Again, some sort of PCB coating should negate condensation issues. And you are taking into account your run lengths (yay!) and hence using my generally preferred centralised solution. (Unlike and old example of a 200m cable to a camera where the converter was therefore placed at the camera end.) Being battery powered, the voltage probably isn't too critical. IE - typical alkaline batts are up to 1.65V hence your timers should tolerate 3.3V if not 3.6V for other cell types. And it might operate anywhere down to ~2.0V tho I'd assume not that low... maybe 2.7V??? If they were solenoid type valves I'd probably adjust the vregs (dc-dc convs) for 3.0V at the valve end with valve energised provided 3.6V is not exceeded with valves de-energised. But if they are motorised and only draw current whilst changing state I'd merely ensure they operate ok at whatever voltage you set tho I might then set for a higher voltage, say 3.2 - 3.5V. Circuits like this can be tricky. The timer might handle 5V or more but solenoids can burn out with overvoltage (ie, overcurrent) and motors can burn out with undervoltage - ie, they never develop the power to get there so they just heat up. Luckily electromagnetic devices like that tend to be quite robust and tolerate relatively large deviations from "nominal" operational voltage for reasonable times. There's also the impact upon overall current draw from the battery but I doubt that's a concern and it would probably only be 20% difference if that.

Thanks again. 3.5v should drop to 2.7v at 30 feet. I feel safe at 3.5v. I will run more test over the weekend and post back.