12 volt power supply

I am thinking of installing a wheelchair lift in the back of my 2006 Odyssey for occasional use. That would enable me to easily put my father's power
chair in the back of the minivan once in a while. These things take about 20 amps. There are 3 12 volt (10 amp) power supplies in the minivan, and rather than permanently installing a wire to the battery as is recommended, since the lift will only be used once in a while, I was thinking of making a connector so I could connect all 3 power adapters already installed by the factory to the lift when I use it. I presume that 3 times 10 amps will give me 30 amps which is 10 more than it needs. Not being an electronics genius, anyone knows if there is a problem with my idea? Thanks.
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Do it right and run the wire to the battery and place the fuse at the battery. The 10 amp outlets in the car are probably all on the same fuse so you will still only have 10 amps.

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Art wrote:

Bad idea. You will need a separate 30 amp circuit. The existing power outlets are most likely all on one circuit, but as multiple plugs in your home can all connect to one circuit.
You need someone well versed in automotive electronics to do it right.
John
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John Horner wrote:

I'll second that (and Woody's post as well).
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That was what I figured. Kind of hate to add a high amp wire the length of the chasis even if done by someone who knows what they are doing. Seems like a problem waiting to happen.

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On Thu, 02 Nov 2006 20:36:13 GMT, Art wrote:

Not if the fuse is up front, by the battery. A short further back will just blow the fuse.
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Art wrote:

Not if it's done properly. This is common practice for high-powered stereo systems, often with much larger wires carrying far higher current. Your purpose shouldn't require anything bigger than 6ga. or at most 4ga. (see http://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html ) - imagine double-0 gauge wire over 3/8-inch thick!
Grommets anywhere it passes through metal, an appropriately-rated fuse at the battery end, and all should be fine (be sure whoever does it upgrades the battery's ground wire if necessary too - a too-thin ground lead defeats the whole purpose). If nothing else, any decent car-audio shop should have the wire in stock in their install bay and should have the job done in less than an hour.
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Go to a Professional 2- way radio dealer...I was a installer in one for years. Do not try to do it without info! I saw where a fire chief thought, he knew it all, and installed a 50 amp light bar on his brand new fire red pickup.
He was answering a fire call one day, when his truck caught on fire and burnt,total, before his own fire dept was able to put it out! He took # 12 solid wire, from the battery, no fuse, thru a ragged hole in the firewall, just a bad job! Don't take changes!
d

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Andy & Carol wrote:

Oooooo that smarts!
As I stated before, any "good" car-audio shop should be able to do the job as well, as they'll be experienced with, and have the wire and accessories for, high-current installations.
One other thought, though, Art: you may want to consider using a separate battery with a battery isolator to run your lift. The isolator will allow both batteries to be charged normally, while preventing the lift from draining your main battery and potentially leaving you stranded. Again, any high-end car-stereo shop should be able to do it for you, OR a place that does camper installs/conversions, which is probably the most common use of isolated two-battery setups.
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Thanks to everyone for the valuable posts.

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Art wrote:

One note.. If you do run new wires to the battery, fuse *both* the positive and negative. MK
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Too often overlooked! In the event of failure of the engine ground the negative lead can carry massive currents, including the starter current.
Mike
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Michael Pardee wrote:

True'dat. Which is why my preference would be to use the vehicle chassis ground, and beef up or duplicate the battery/chassis ground cable(s).
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I am considering another choice. Other manufacturers make rechargable batteries for the same type of application. The batteries can turn out 25 amp but the charger only requires 7.5 amp. I could keep this charge plugged into the ac outlet in the back of the Odyssey and avoid the extra wiring job and issues. I wouldn't consider this if the lift got frequent use but it will probably be used once per week at most.
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Art wrote:

That might be alright, but a few things to consider:
What is the cost of the "custom" battery/charger system? Once again, there is nothing wrong with having heavy wiring to the back of the vehicle; this is common in car-audio applications and any competent installer can do a good job of it, potentially cheaper than the setup you're talking about once all the other considerations are taken into account.
Make sure the battery in this setup is able to provide not only the necessary current, but has the necessary capacity as well (rated in Ah, or Ampere-hours). It's not much use if it has the juice to get the lift down, but then needs to recharge for a long time before it can get the lift back up. You also want to be sure the system isn't charging the auxiliary battery if the engine isn't running, or you risk running down your van's own battery and not being able to start it.
Finally, if the battery you're talking about here is a standard lead-acid automotive type, you don't want it exposed within the passenger area, as all batteries of this type generate hydrogen gas when they're charging. It should be in its own enclosure, ventilated to the outside... unless of course, your van is named The Hindenburg. (If it's a gel-cel battery, you're okay, although most of those are not very high capacity).
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