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Electronics for Dogs III · 11 October 05

Before we turn over the chalkboard to the critters let’s talk about relays a bit.

Automotive relay

Relays are electro-mechanical switches powered by a small voltage applied to the coil of the relay. The coil is just a bunch of wire wrapped around an iron core, kind of like the electro magnet we made as kids by wrapping wire around a nail and hooking it to a D cell.

Same thing with the relay: power to the coil turns it into a small magnet that pulls on a piece of metal. The piece of metal is a lever that closes (or opens) one or more switch contacts.

The average car has in the neighborhood of a two or three dozen relays that look just like the one pictured here. Relays are used to turn on wipers, turn signals, brake lights, starters, you name it.

Electronics for Dogs Part III

One reason relays are used is to cut down on prices and keep the size of wires down. When you flip on the windshield wiper you are closing a relatively low amperage switch (cheaper) which is connected via a small wire to a relay, either under the dash or in the engine compartment. The relay has heavier duty contacts and wiring, able to turn on and off the higher current to the wiper motor.

An EV uses a few small relays and one or more HUGE relays. The big relays are still powered by the car’s 12vdc, but they switch hundreds of volts and amps.

Now on to Electronics for Dogs Part IV

Comments 9
  1. — Faith Henricksen    Oct 11, 2005 20:31 PM    #
    What? No CAT?
  2. — Monica Deangelis    Oct 11, 2005 20:31 PM    #
    All I hear about are the 12v batteries that are currently being used by the automotive industry. Hasn’t a 48v battery been developed? Don’t the battery companies want to invent something that could be used to advantage in an EV? And what about the new solar panels that are flexible and can withstand outdoor elements? How about the conventional solar cells as the roof of the car being used to recharge the battery?
  3. Greg Gullatt    Oct 11, 2005 21:15 PM    #
    I think the cat is out visiting…...
  4. — Dan    Oct 11, 2005 23:11 PM    #
    Yeah, but ours goes to “11”... How ‘bout that? :P
  5. Jerry Halstead    Oct 12, 2005 07:59 AM    #
    Cat? What is cat?

    Hi Monica: no guarantee that a higher voltage battery would be of any help (or hindrance) to EVs. Still the same tech, although you might save a bit on space. I’d worry that it might make things worse in that you’d have to replace a more expensive battery if one cell went bad (it happens). And, yes, if there was enough interest (i.e. $$$) then batteries companies would focus more on making EV batteries. Chicken and Egg problem, although hybrids may be the incentive the industry has been waiting for.

    I’m still unconvinced that solar cells are worth the cost and effort on an EV (home/office install is another thing). Still, there’s a few EVs that use them, check out Larry’s and Peter’s electric vehicles.
  6. — Michael    Oct 12, 2005 11:35 AM    #
    Though, neither of those coversions are able to rely entirely on their solar cells to recharge the batteries. Peter has a huge solar array on the roof of his van and it only recharges 25% of his 26 mile daily commute. I like the ‘solar recharge station’ idea better. Have you considered setting up something like that over your garage, Jerry?
  7. Jerry Halstead    Oct 12, 2005 21:40 PM    #
    I am. We have a roofing project coming up next summer and that’s being considered.

    Not sure yet if we’d just sell back to power company (use them as the battery) or have a set of batteries. If it wasn’t such a mechanical nightmare it would be cool to have two battery packs: one that stays home and charges and/or backs up the house, the other in the EV.

    It’s not too farfetched to use the EV as a backup power source for the house. We’ve had power outages in the past where I’ve hooked a small UPS to the EV batteries to power our pellet stove and freezer.
  8. Greg Gullatt    Oct 13, 2005 13:34 PM    #
    I was thinking about that yesterday, using the EV as a backup power supply for the house, then I thought why not have a second set of batteries built in/on a light weight utility trailer. It could supply the house or hook up behind the EV for a backup pack using a quick disconnect connector/harness. Could even have an automotive diffy out of a small rear wheel drive vehicle with an alternator/generator running off of the differential.
  9. — Jeremy W    Jun 22, 2008 18:59 PM    #

    the utility trailer is a good idea but if you use a 120+ voltage setup then you couldn’t use the standard trailer connector because you would fry the wires. You could probably fabricate a quick connect. If you can tell me and i might do the dame thing.