12V powered AC outlet timer

[Daox]

In combination with going alternatorless, I'm also looking to add a block heater and possibly battery warmer. This poses a problem when I plug in at night. I want the charger to start running immediately, but I do not want the block heater and battery warmer to run until a couple hours before I leave. Now, I could use two extension cords, one on a timer and one not on a timer, but I'm not real fond of that idea. The alternative is to use a 12V powered AC timer. However, the ones I've seen for sale are all $60+, and that is a bit much.

My initial thought was do make an arduino project out of it. Then, thankfully I was in contact with my charger supplier (also an EV owner) and gave me this link:

12 Volt Programmable Timer Switch - Electronics

The article suggests you can use a programmable thermostat (the ones that control your household furnace) as a timer. I'm not sure if the relay in the themostat is beefy enough to handle a block heater, but you can always add another beefy relay to the system that can handle it. Seeing as how you can pick a programmable thermostat up off ebay for just about the cost of shipping, this looks like a great alternative.

Does anyone have any other ideas?

[NiHaoMike]

Some digital timers have battery backup.

[brucey]

Why not just use an extension cord with a multi prong outlet, and put the timer on one and plug the other directly in? Not as fancy, but just as convenient.

Further, how big is your charger? With a 10 amp charger, under short trips, an hour of charging should do it.

[dcb]

what brucey said. you have two plugs on your car, one for the charger that goes straight to the wall and one for the heater/battery warmer that goes to a beefy timer plugged into the wall.

[Daox]

Originally Posted by brucey

Why not just use an extension cord with a multi prong outlet, and put the timer on one and plug the other directly in? Not as fancy, but just as convenient.

Basically because I don't want to. I've made compromises with modding the car and how I drive (limited range with alt delete, full grill block makes coolant fan turn on on longer than normal trip, etc). I don't want more compromises, I want this to be easy and not an inconvenience. I want to plug in one thing for the night and be done. I also don't think its that difficult to do, so its not going to be a hangup.

Further, how big is your charger? With a 10 amp charger, under short trips, an hour of charging should do it.

The charger is 7A. I haven't measured to see how long its in operation before it gets my battery recharged. The time will vary depending on how much electronics are used obviously. In winter the usage will be much higher since I have to use headlights on my morning and afternoon commute.

[dcb]

How do you want to control when the heater turns on? Is it the same time everyday? Just weekdays? Should it turn itself off after x-amount of time? Do you need a user interface (lcd+buttons) to set the time? Do you want to schedule the next on-time and duration? Is it scheduled based on a realtime clock or some # of hours in the future? or be able to cancel the next warmup? how may button clicks can you tolerate?

[Daox]

Those are good points dcb. I thought about that as well. I do not use the Paseo every day. In fact, normally I only use it a couple times a week. To take care of the scheduling problem I would set up the timer to turn on 1hr before my normal leave time. This would turn the heater on every morning its plugged in (likely including weekends if I used a cheap thermostat). To fix this problem, I was planning on adding a switch in line with the AC power to the thermostat. That way, if the thermostat relay kicks in, the switch still blocks power to the heater.

That takes care of pretty much 99% of my trips in the Paseo. However, if I wanted to use the block at a time not scheduled on the thermostat, I could easily install a bypass switch to bypass the thermostat (and other switch), so I plug in and it heats up right away.


I do have a 3rd option now. I was talking with Darin earlier today about how large of a heater to get. The basic consensus was that larger is better here. I have settled on a Kats 1000W circulating tank type heater for the Paseo. This allows pretty decent warm up times. Below is a graph Darin made of his Metro's warm up times with two block heaters going totaling 1100W. In 1hr, he is able to get very close to operating temperatures. Even running for 30 minutes results in a very respectable temperature.




With this very short warm up time, I could use a remote control AC switch like they use for Christmas lights. I could get up in the morning, flick the switch, get ready, and it would be warm enough by the time I get out to the car.

I'm now leaning in this direction. Its much simpler, easier, and the fast warm up allows unplanned trip heating much more viable.

[MetroMPG]

I like the remote idea.

Like you said, it's all about convenience, and convenience matters more in the winter.

Also, if you get into the habit of plugging the car in when it's parked, you can pre-heat it for "unscheduled" / spontaneous trips from the comfort of the house with a remote.

[Ryland]

Amazon.com: Woods 59203 Digital Lamp and Appliance Timer, Repeats Weekly with…

Looks like it should work for your needs, the battery back up recharges off the ac power, you should be able to find a 7 day or 5 and 2 day timers (week day, weekend) that has battery back up like that as well, $12 plus shipping.
If you find one that you like but that can't handle the amps, solid state relays seem to be pretty cheap, I have one that can handle up to 60 amps at 240 volts and I think it sold for about $10 but only works with ac because it closes it's contacts in the middle of the sign wave, when it's at 0 volts.