Charging 2007 Prius 12 Volt Battery through the Fusebox Connection?

I've often thought about doing that, just to see if there's any differences there compared to connecting my charger to the battery directly, but never get around to it. I can't think of any reason it would be a problem, but maybe my procrastination on trying is based on something? Wonder what others who see this thread will say?

 

I'm pretty much constantly charging our 3rd gen's 12 volt, from the under-the-hood fuse box, via a wiring harness with plug for my specific charger, tapped onto the 12 volt input to the fuse box, amounts to the same thing. Second gen Owner's Manual recommends a charging limit around 3.0~3.5 amps IIRC? An up-to-date smart charger is your best bet: they go through a charging regimen, then settle down to trickle charging, can be left on indefinitely.

 

So the only difference is a tiny bit of electrons lost to resistance because the charge has to travel further to get to the battery?

 

Guess so; they get from the fuse box to battery pretty fast.

FWIW: Owner's Manuals say to always charge the battery out of the car. Which I don't think I've ever done. I lie: I did once, when I got a replacement battery.

 

Why exceed the manufacturer’s charge rate? If you’re pressed for time, remove the battery from the car and charge the living daylights out of it. That way you only destroy the battery, not the vehicle’s internals (worse case scenario). Or keep life simple and charge at a rate recommended by the manufacturer. It’s called the KISS Principle (Keep It Simple Stupid) (no offense intended to most people (just those who abuse their equipment, which I don’t suspect Canadians and the OP are guilty of. ))

 

I've found that to be the way I do it for a great condition '85 Toyota truck I'm doing work trade to buy. I think it has a voltage leak so I fixed it by having two 12v batteries that I rotate.

 

it would be a problem, but maybe my procrastination on trying is based on something? Wonder what others who see this thread will say?

 

not really the best time of year to be experimenting with much of anything car related in our area.
If the temps haven't started falling yet further east in your location, it might be surprising when you get in your car next time, if that will be in the next few days.

 

I've charged through the jumper post under the hood. I didn't excede 1.5A. But looking at how thick that wire is it should be able to do a lot more.

Yes, the longer the wire the more the loss. But that goes for adding any sort of extension cord or similar. I wouldn't worry about a wire that goes from the front of the car to the rear unless we're trying to charge a train.

 

That cable resistance is totally insignificant, assuming a reasonable charge current.

 

In most cases that's true... But with a dying 12v battery it becomes way more pronounced of a problem. That's why many on here insist on taking a voltage reading at the jump points rather than directly at the battery...

 

That cable to the back of the car is selected and fused for 120 amps.

At a 4½ amp charge current, any losses there will really be negligible.

People who are diagnosing a problem with the car may suggest measuring voltage at the jump point, because that way you will catch possible damage or high-resistance connections along that cable, which you would miss by just measuring at the battery. But that's kind of a different situation from just wanting to charge up the battery, when no wiring damage is suspected.

 

Voltage drop is dependant on amperage. No amps, no voltage drop. 120 amps (or there abouts) means a huge voltage drop. The only way around the voltage drop at high amps is to either shorten the wire or make it fatter.

 

I wouldn't quick-charge a battery of that size anyway, just too hard on the little things.

 

More specifically, voltage drop (in a simple wire) is proportional to amperage. No amps, no voltage drop, 1 amp, a certain voltage drop, 120 amps, 120 times that much voltage drop.

Whether the drop at 120 amps is 'huge' or not depends on the choice of wire. If you tried to pass 120 amps over a wire that had been selected to carry 1 amp, you would have a 'huge' voltage drop (and other impressive effects, at that big an overcurrent).

120 amps over a wire selected and fused for 120 amps will give a voltage drop no higher than the designers expected. And if you're passing 1 amp, or even 4½ amps. over a wire selected for 120 amps, your voltage drop will be tiny.

 

No, it doesn't. The problem then is the "dying" battery, not the cable.