Simple 12V timer needed

plexed

I have a 60W panel set that runs an electric fence around my yard, and I want to also have it run a ventilator fan in my garage. I need a simple 12V timer that can control about 5A. I only want to run the fan a few hours a day, so a dusk-to-dawn won't work. It also needs to be able to handle cold weather, so a programmable thermostat won't work.

The only one I see out there is the Flexcharge digital, but that is way overkill at $75. Just looking for something simple like the dial I use for my Xmas tree that cost me 10 bucks.

Any help appreciated.

mike95490

Re: Simple 12V timer needed

There are some "digital" 120V timers that may run on a small mod-sine inverter.

Does the venting need to happen daily, regardless of cloud cover, or weather ? If you need a fan in clouds, that's going to take a lot of battery power.

Would a fan connected to a PV panel, to run when sun is out, be suitable ?

2) the panel running the fence, will generally not run anything else, it uses it's power to charge the fence battery. if you siphon some of that power away, for a fan, you run a risk of having the fence go dead. if they could have gotten away by selling a 50W panel, they would have, and kept the price difference.

plexed

Re: Simple 12V timer needed

Thanks for the response.

The fence uses hardly any power at all. Fence charges typically sip electricity rather than chug, so I should have plenty left over for the fan. I went hunting last month in bear country and used an electric fence around my tent that ran on two AA batteries.

I bought the 60W panels separately, so it wasn't sized by the fence maker.

If I run low on power, I can just cut back on the time the fan is on. It is used to get stale gas and grass clipping smells out of the garage mainly.

crewzer

Re: Simple 12V timer needed

Switching DC can be rough on contacts, so DC-rated switches, relays, etc. tend to cost more than similarly rated AC products.

Morningstar makes an interesting charge controller / timer that might be of interest to you. See: http://www.morningstarcorp.com/en/support/library/SL.DAT.Datasheet.01.ENG.pdf

HTH,
Jim / crewzer

plexed

Re: Simple 12V timer needed

That device would be PERFECT if I didn't already have a charge controller. But spending $90 to run a $10 fan?

Seems like a good niche opportunity exists for someone to make a cheap 12V timer.;)

banjorene

Re: Simple 12V timer needed

Noticed this on ebay dont know if link will work

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=370103122657&ssPageName=MERC_VI_RCRX_Pr4_PcY_BIN_Stores_IT&refitem=370103117084&itemcount=4&refwidgetloc=active_view_item&usedrule1=CrossSell_LogicX&refwidgettype=cross_promot_widget&_trksid=p284.m184&_trkparms=algo%3DCRX%26its%3DS%252BI%252BSS%26itu%3DISS%252BUCI%252BSI%26otn%3D4
Rene

Brock

Re: Simple 12V timer needed

A litle more pricy, but something like this
www westsidewholesale com/index.cgi?CATEGORY=375
I have one and run 12v lights on it. It uses the battery to power the timer part and snaps a tiny latching relay open or closed. I would think it would work fine, unless the fan is pretty big, then you might need a second 12v contactor.

Otherwise a good old spring wind timer, but of course you have to manually twist it on.

plexed

Re: Simple 12V timer needed

Brock, you the MAN!:cool:

plexed

Re: Simple 12V timer needed

Well, I got the Intermec timer, and I think I immediately blew it out with the fan motor. The timer is rated at 4A, whihc is what the fan is at, but I bet the fan has a much higher start-up current and that killed the timer relay.

Any other ideas?

Brock

Re: Simple 12V timer needed

That’s weird. The one I have is rated 15 amps, it was like $25 at home depot.

Well you could use a 12v relay and turn on the relay with the digital timer. Radioshack has an automotive 30 amp relay that should handle it no problem.

mike95490

Re: Simple 12V timer needed

What the heck is your fan ? from a car radiator ? (those can take 30A @ 12V)

plexed

Re: Simple 12V timer needed

It a marine bilge fan. 4A at 12V steady state.

mike95490

Re: Simple 12V timer needed

Not knowing all the specs on the fan, I think you could likely get more air movement from a different style of fan, bilge blowers are usually squirrel cage fans, and do real well to move air thru lots of ductwork.

A roof mounted turbine ventilator (non-electric !) would move air 27/7 when there is a slight breeze. A brushless DC fan would likely move more air for your 4A then the blower, and have a much longer lifetime.

But you have the blower now, and it has a brushed motor in all likelihood. The motor is likely sending a high voltage spike into the system, as the windings roll past the brushes, like a vibrator high voltage coil. A diode installed at the motor should soak up most of that spike.
I'd look at a 100V, 1A diode

Blower/fan comparisons:
blower
http://www.farnell.com/datasheets/71404.pdf
12V .37A 4.4W 12.7CFM
&
DD523612K 12v 45.6w 3.800a 200cfm

fan (usually quieter than blowers)
http://db.sanyodenki.co.jp/product_db/cooling/dcfan/group_pdf/1035871628.pdf
12V .15A 1.8w 17CFM
&
031086 12V 3.4A 205cfm

BB.

Re: Simple 12V timer needed

We have had a few threads here about installing solar powered attic fans... And the end result has pretty much been--add roof passive ventilators (like turbines if you really need a lot of air flow) and make sure you have enough screened air inlets too to help with air flow.

Solar fan systems are typically expensive, small (when compared to a 120 VAC true attic ventilator van) and don't last very long (a few years) before needing repair/replacement... And, some folks have found that just adding the extra openings for the solar attic fans was enough to drop their attic temperatures (only found that that attic fan had failed by checking the fan--the attic temperatures did not rise when the fan failed).

And for DC switching--you can use a "reverse biased" diode to protect drivers/switches from inductive "kickback" when switching DC loads...

Basically, one place to use a diode is an electronic devices controlling a relay... You place a diode "Backwards" across the relay coil (diode cathode to + lead driving relay coil).

You can do the same thing for driving motors (or other inductive loads) with switches/relays... You put a diode backwards across the DC inductive load.

In both of the above cases, when a switch "opens" (turns off), the inductor (relay coil, motor windings, etc.) want to keep the current "flowing" in the same direction... This causes the inductor to generate very high voltage across its terminals (hundreds of volts or more)--which causes a spark across the relay contacts and/or damages a transistor/FET switch... The reverse biased diode simply allows the current to flow through the diode until the energy is dissipated.

An alternative is using a capacitor across the relay/switch contacts. Just like the old ignition condenser across the points in a car's ignition system... Sizing the capacitor is a bit more of a pain though--and using a diode is easier (assuming you don't install it the wrong way in your circuit and cause a dead short through the diode).

Either, properly done, will greatly improve the life of your DC switches.

-Bill

plexed

Re: Simple 12V timer needed

The garage is in the basement of a building, it does not have a roof that a fan can go in to. The wall is surrounded by trees, so I can't use a regular solar-powered attic fan.

The system has been running fine on AC for years, I am just trying to simply change it over to DC to run it off solar-generated DC I have coming into the building.

I appreciate all the advice about attic ventilation, fan types, etc., etc., etc., but really all I want is an inexpensive 12 DC timer that will reliably run about 4 A.

I tried the other Intermec model that does 15A, but that doesn't even seem capable of switching DC. It seems to be some sort of solid state relay that requires the 120VAC to operate.

I've seen he FlexCharge timer for $90, but doesn't someone make a 12V 24hr dial timer like the 120V AC models used for Xmas lights? The Flexcharge has a microprocessor, you can set a multitude of on/off cycles, it compensates for daylight savings time, etc, etc. Cripes.

The other option is to run an inverter and up it to 120VAC and use the normal stuff and the AC fan I originally had, but the inverter too much standby current for this application.

This is wayyyy too difficult.

System2

Re: Simple 12V timer needed

plexed wrote: »

Well, I got the Intermec timer, and I think I immediately blew it out with the fan motor. The timer is rated at 4A, whihc is what the fan is at, but I bet the fan has a much higher start-up current and that killed the timer relay.

Any other ideas?

---

Wouldn't be surprised if the timer contacts open rather slowly, which as mentioned earlier is fine with AC, but with a 4 amp DC inductive load would be the perfect arc starter. Puff go the contacts.
FYI, I've often use a high amp rating FET in place of a relay in such circuits. Has worked just fine for me. Of course I always use a diode across inductive loads to shunt off spikes. One place I use the FET is to control my air exchanger, which I converted to brushless 12 volt DC. To save power etc, wanted to sometimes run the motors half speed. Motors didn't like 6 volts, so ended up with a NE555 controlling an FET. 10 minutes on, 10 minutes off. Works perfectly, no contacts to arc, no relay coil drain, no clicking and snapping.

System2

Re: Simple 12V timer needed

plexed wrote: »

doesn't someone make a 12V 24hr dial timer like the 120V AC models used for Xmas lights?

---

Probably not. Highly unlikely. Reason being, the market for such a timer would be next to nil.
Sorry

plexed

Re: Simple 12V timer needed

Wayne - Do you have a wiring diagram for your 555 timer/FET setup? Sounds like it would work for my case. Back in my EE days I used to do a lot of breadboarding, so it might be fun to get back into that again.

Thanks much

System2

Re: Simple 12V timer needed

Haha, didn't have a drawing, was all in my head, but I'll get a schematic drawn up and email it to you, as soon as I get a chance, next day or two.
In the meantime, here's a calculator:

http://ourworld.compuserve.com/homepages/Bill_Bowden/555.htm

Cheers
wayne

plexed

Re: Simple 12V timer needed

Great - I've decided to kill 2 birds with one stone and do this as a science fair project with my high school daughter. She gets a cool project for the December fair and I get my cycled fan.:p