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> stupid human questions, 12v => 110v => 12v
machina
post Mar 18 2005, 12:58 PM
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Haven't had a problem with the battery running down yet but...

if I wanted to give a quick charge at the track, could I...

run an inverter in the truck to power a small 10 amp charger, to boost the battery between runs?

Will it run my truck battery down in a 1/2 hour? How big of an inverter will I need to run the charger? I've checked different brands specs but they don't seem to tell what the power consumption is.
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ArtechnikA
post Mar 18 2005, 01:04 PM
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QUOTE (synthesisdv @ Mar 18 2005, 01:58 PM)
If I wanted to give a quick charge at the track, could I...

...just use jumper cables to connect it to the truck battery ? yes...

or if you even think it might be an issue, get a solar panel charger and just always connect it.

Pegasus sells some nice quick-disconnect grid-power battery connectors -- the dry-cell formula-car guys use those a lot...
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TonyAKAVW
post Mar 18 2005, 01:05 PM
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To run a 10 amp charger you will need a 1200 watt inverter (minimum). (120V*10 amps=1200 watts)

At 12 volts, this equates to 100 amps. Given that inverters are not 100% efficient, you can probably add another 20% to that, or 120 amps. It might be less than that, but just to be safe.

For a half-hour charge you are looking at a total energy consumption of somewhere 60 Amp-hours. That is probably more than the total stored energy in your battery, or at least enough to bring the voltage down to where the starter won't be happy.

Another way to look at it is you are dumping charge from one battery to another through a conversion that has substantial loss. So unless the track car's battery is significantly smaller than the truck battery you WILL have problems.

Why not skip the inverter/charger all together and use a set of jumpers to charge the battery form the truck using the truck's alternator. OR, if you don't want your truck running for 30 minutes, buy a small generator. Or, get a large bank of batteries for your truck. Or maybe just two or three batteries for your track car that you can take and swap. No charging necessary until you get home.

-Tony
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machina
post Mar 18 2005, 01:07 PM
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QUOTE (ArtechnikA @ Mar 18 2005, 02:04 PM)
...just use jumper cables to connect it to the truck battery ? yes...

or if you even think it might be an issue, get a solar panel charger and just always connect it.

Pegasus sells some nice quick-disconnect grid-power battery connectors -- the dry-cell formula-car guys use those a lot...

then isn't there a chance the 914 will be charging the GMC?

if you bridge 2 batteries, do they achieve some kind of electrical zen?

I didn't know those solar chargers worked so well. Don't they have like 500ma output?
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TonyAKAVW
post Mar 18 2005, 01:10 PM
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QUOTE
or if you even think it might be an issue, get a solar panel charger and just always connect it


Solar panels don't produce much power for a given size. I saw an ad on Harbor Freight's web site for a 45 watt panel for $200. It's basically a 3 foot by 3 foot square area (three panels). 45 watts is not a lot of power, its less than 4 amps at 12 volts. (or with perfect conversion (not possible) 0.4 amps at 120volts). So figure 10 times the area to make the kind of power that would really make a difference. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

-Tony
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scotty914
post Mar 18 2005, 01:12 PM
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sorry tony, its 10 amps at 12 volts not 120

so 10 amps at 12 is 1 amp at 120 volt or 120 watts

so the inverter needs to put out 120 watts at 120 but as tony mentioned there is a loss

but you average 300 watt inverter can do it with out a problem

but i would just use jumper cables or get one of those jump packs, that way you can have a small compressor for tire pressure changes as well, if you buy one with it
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TonyAKAVW
post Mar 18 2005, 01:15 PM
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QUOTE
if you bridge 2 batteries, do they achieve some kind of electrical zen?


Yes. Think of it as two glasses of water. One full, one empty. But when you pour one glass into the other, you lose some of that water to in one case, the conversion inefficiency of a power supply and inverter, or in both cases to the internal resistance of the battery. In the end, the total amount of water is less. In the case of connecting the two batteries together, they will both equalize at some voltage. For an inverter/charger one will be drained more (because the inverter has the ability to suck more out of a battery than just bridging the battery) and the other will have a higher voltage. However, the total amount of eneergy will have been reduced more than for the first case.

Just take a second battery if you are worried, its probably the cheapest way to go if you don't want to run the truck for a while.

-Tony
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machina
post Mar 18 2005, 01:15 PM
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QUOTE (TonyAKAVW @ Mar 18 2005, 02:10 PM)
QUOTE
or if you even think it might be an issue, get a solar panel charger and just always connect it


Solar panels don't produce much power for a given size. I saw an ad on Harbor Freight's web site for a 45 watt panel for $200. It's basically a 3 foot by 3 foot square area (three panels). 45 watts is not a lot of power, its less than 4 amps at 12 volts. (or with perfect conversion (not possible) 0.4 amps at 120volts). So figure 10 times the area to make the kind of power that would really make a difference. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

-Tony

great ideas guys, thanks.

my little battery tender only output 1 amp (I think), so 4 amps isn't bad.
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TonyAKAVW
post Mar 18 2005, 01:17 PM
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QUOTE
sorry tony, its 10 amps at 12 volts not 120


oops. stupid mistake. Maybe I should go work for Nasa and help design their Mars missions. I hear they allow mistakes like that all the time.
(IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif)


-Tony
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bd1308
post Mar 18 2005, 01:19 PM
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why dont you just keep the truck running, put a huge diode on a pair of ol' jumper cables and just use that? It would be so cheap and awesome....make sure you put some danger stickers all over the jumper cable so people all around will stop and look at your crazy jumper cable.... use the alternator in the truck to charge the 914 battery while its running. (IMG:http://www.914world.com/bbs2/html/emoticons/smilie_pokal.gif)
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lapuwali
post Mar 18 2005, 01:32 PM
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You don't even need the diode. The alternator will basically just be charging both batteries. I'd arrange a quick-disconnect system using the large charging connectors you can find from Pegasus and others. It's not cheap, but it's MUCH less likely to result in an accidental short caused by someone in a hurry. Just attach one quick disconnect to the battery in the truck, and another to the 914. No need for an inverter at all.
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bd1308
post Mar 18 2005, 01:37 PM
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QUOTE (lapuwali @ Mar 18 2005, 01:32 PM)
You don't even need the diode. The alternator will basically just be charging both batteries. I'd arrange a quick-disconnect system using the large charging connectors you can find from Pegasus and others. It's not cheap, but it's MUCH less likely to result in an accidental short caused by someone in a hurry. Just attach one quick disconnect to the battery in the truck, and another to the 914. No need for an inverter at all.

well i guess thats true......good point friend
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davep
post Mar 18 2005, 01:41 PM
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I'm with James here. The best solution is basically a set of booster cables to charge off of a running vehicle. It will take time though. A spare battery, one to run, the other on charge would be good.

An idling engine really doesn't charge as well as running at speed. You need to get the voltage up to 14 or so to charge well. Even then you may need a couple of hours to bring it up. The last few hours on a charger don't do much. Your best bet by far is to fix the alternator.
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john rogers
post Mar 18 2005, 01:41 PM
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Here's a great excuse for trying something new....Get one of those external batt jumper plugs that all the F5000 and CanAm cars use and a spare batt and then plug it in when needed. It would end any need of chargers or things like that?
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machina
post Mar 18 2005, 01:42 PM
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already got the plug in the car.

have matching plugs on my garage charger and jump pack already too.

so maybe Ill install a plug in the truck and be done with it.


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machina
post Mar 18 2005, 01:44 PM
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QUOTE (davep @ Mar 18 2005, 02:41 PM)
The last few hours on a charger don't do much. Your best bet by far is to fix the alternator.

No alternator in the car.

And I have one of the 80's style blower housings that Jake found. Supposed to cool better but you cant run a stock alternator with it.

My sport race did have the alternator driven off the half shaft with a belt, but it was a PIA.
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davep
post Mar 18 2005, 01:52 PM
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That being the case, get a spare battery and some booster cables. The car batteries don't like what you are doing with it, and will not last as long. You will need to put them on charge as often and as long as possible. Contact me if you need more help. I have learned how to test batteries, design battery chargers & power supplies, and also work with inverters up to 1500 watts.
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machina
post Mar 18 2005, 01:55 PM
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QUOTE (davep @ Mar 18 2005, 02:52 PM)
Contact me if you need more help. I have learned how to test batteries, design battery chargers & power supplies, and also work with inverters up to 1500 watts.

Thanks Dave,

I have a regular red optima 34 now but they make a deep cycle blue that is supposed to be better for full discharge.

Should I go to that one when this battery get flakey?
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Brando
post Mar 18 2005, 01:56 PM
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I think it's time to incorporate this into a vinyl covering for your car, wire it up to the battery.
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ArtechnikA
post Mar 18 2005, 01:59 PM
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QUOTE (TonyAKAVW @ Mar 18 2005, 02:10 PM)
45 watts is not a lot of power, its less than 4 amps at 12 volts.

IOW - just less than half the power available from the 10A charger.

since there is already no problem, 4A should be enough to keep it that way.
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