MacGyver a flat 12v battery from the HV ?

Likewise, Dave; it never gets colder than about 30F here in the San Francisco Bay area. So our "cold" season is not all that cold, relative to how SOME areas get cold.

~ dan ~

 

Re: i think

You are technically correct, but this would probably be a really bad idea. By pulling current out of one or two modules you would potentially unbalance the pack. Once the pack is out of balance, the car won't start. At this point I don't think even the Toyota super duper charger can help you. You'd be on your own to find a way to rebalance the pack or replace it.

Rob

 

Ok, here's a thought. Probably still a bad idea, but its a thought.

The whole HV -> 120AC -> battery charger UPS based idea would probably work, but requires a lot of equipment. In theory you could power a 12V battery charger with a switching mode power supply directly off the HV battery. Here's a possible example:
http://soneil.com/Completesets/SPEC1205SR(REV 03).17-Jun-04.pdf

To be safe you'd want to check with the manufacturer to make sure it will run on DC and over what voltage range. If it would work at ~220VDC, you're looking at a $50 HV battery powered aux battery charger If that doesn't do it, a Vicor Batmod would but now you are looking at a couple hundred bucks.

A secondary battery is probably a better idea, but you'd need to have a way to top it up once and a while. Something like the isolated start/aux batteries run on RVs, or 4x4s.

Rob

 

FYI, pepboys is clearancing an 18AH jump box for $20 if someone wants to go the non-MacGyver route

http://www.fatwallet.com/forums/messageview.php?catid=18&threadid=796629&start=0

Rob

 

You guys are trying to make this harder than it is. Here is the way I did it.
http://www.wbcoxco.com/priusbat.htm

The only maintenance is to top off the charge once in a while. I try to do it once a month, or something like that.

Sorry, didn't realize that I had already posted this earlier.

 

You could have run permanent cables and a large, well-insulated switch. If wired in parallel, then the car can "accidentally" charge that battery as well in one simple trip, and you can take it out of the circuit for most of your driving -- that way, it's always there and always charged just in case something bad happens and your regular battery is always charged?

~ dan ~

 

One of the most elegant things that the EV1 did was to provide a simple button under the dash for this very purpose. You could be parked there with enough energy in the traction pack to run your whole house for a couple of days... but if the 12V Aux battery was dead, the car wouldn't move. So you press this button and it fires up the inverter manually to charge the 12V battery from the 300+V traction battery in short order. FANTASTIC to be able to jump yourself in that way. The Rav doesn't have anything like that.

Eventually somebody will have to tell me why every car on the road does not have AUX battery rundown protection built in!

 

There once was a lead acid starting battery with a switch and a small aux 12V pack parallel to the main pack built in. If you had a flat battery you lift the bonnet and flick the switch and the small cells had enough in them for one start, hopefully. I never saw the point in carrying a small 12v battery I might use once before I replaced the battery? Most people never saw the point and the battery was discontinued.

Once a conventional lead acid battery has been run flat a couple of times it goes down hill fast. I have always replaced a battery if I had to jump or push start just once and there was no reason the battery was flat. If the battery is over 4 years old I would replace it even if I knew why it went flat.

I own a car to get places I haven't time to catch a bus to. I also haven't time to mess about with jump starting and battery charging either. At about $100 and with a life of about 4 years batteries are cheap enough and very recyclable, in fact recyclers pay for them.

 

If there was a big diode across the switch the battery would always be charged while you drive and would not discharge unless the switch was turned on.

 

Beautiful. There's the perfect solution. Permanent and almost entirely solid-state.

 

OK Guys -- this MacGivers it! Congrats -- Now could you please specify a switch, diode and cables?
Thanks!!

 

A diode from an alternator There are 6 in each and almost any switch which you can mount up, a simple toggle or push pull with an indicator light a battery from an emergency exit light should do the job and cables I'm not sure, 4mm maybe? Best to include an in line fuse too.

 

Just a comment, Since your everyday voltage in Australia is 240 volts, maybe your exit lights use 12 volt batteries. The ones I have experience with here in the US (the ones at our place of business) all use 6 volt batteries, except the newest ones and they use leds and little bitty batteries.

At first, I was going to use an 8 amp hour battery that I thought was small enough to go in the "secret drawer", but it was a little too big. So my second choice was the 12 amp hour one that I put in the left rear cubby. I usually have an extra one or two of that size around anyway because my electric bicycles use two of them in series for 24 volts. I also have a couple of back-up computer power supplies that use them.

It is good to know that it is charged up and back there "just in case".

 

Yes our emergency exit signs are 12 volt at work anyway. Don't know if it's to do with the 240 volt mains or if it's just an Aussie thing.

I'm no expert on this stuff though.

 

Wow. That's weird; I need two new high amp-hour 12V lead acid batteries for my UPS systems; every time the power flickers I lose my server, firewall, router, desktop PC. The only machines that survive it are my wife's and my portable computers and, oddly, my wife's desktop PC.

Wheelchair batteries are up on account of the recently increased lead prices. Anyone got an idea where I can get a 15-45Ah battery under $150?

~ dan ~

 

Your ups is much bigger than the two I was referring to. I also have a larger one that uses two 18 amp hour 12 volt batteries in series to produce 24 volts. It is currently taking care of two computers and a couple of printers. Don't know about where to find the big ones you need cheap. I get the ones I need on ebay about half the time and locally the other times.

 

Boy, is that too bad. Actually, I bet the UPS is no bigger than what you refer to:

​

This is just... how I roll. The word 'MacGyver' reminded me.

~ dan ~