exchange 12 volt battery?

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I touched a bit of this in Cigar lighters.

 

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Totally broken thread!

 

I just want to correct a misconception here about diodes. Back a ways in this thread it was stated that diodes wouldn't let a backup battery fully charge....

Voltage drop across the diode is a function of forward current. It's typically 0.7v for a silicon diode at some specified forward current. Take a look at the voltage vs current graph for a typical diode at this web page.


As the backup battery approaches full charge the current will drop towards zero and the voltage drop across the diode will also approach zero. The backup battery voltage will fully charge and the charge will taper off as it approaches within 0.7v of the primary battery (due to the diode voltage drop) but will continue to charge slowly until the voltages match.
Gary

 

Any reason? Please enlighten me.

I see some cheap ones (~$25) at pepboys able to output something like 400 or 500A. If we look at some data on start up current of the Prius, it's well under 100A. So there's plenty of margin there.

 

Oh ok. I didn't think about jumping other cars. You are right about needing more juice.

But you were saying if it's not heavy then don't buy it. I was asking if there's any solid reason to heavy = good quality.

 

OK, let me jump in.
The outlet in the dash is completely isolated by a dedicated relay when the car is off. You can't light up anything from there without any mods.
Now the outlet in the console can backfeed to the ACC turn on, which would have the ECUs that operate under ACC to come on, if you had any 12V constant power available. If the OEM battery is dead, you still as of yet do not have any main 12V. The backfeed is blocked in getting to the main 12V feed by a currently open ACC relay.
What is interesting though, is that even with the dash outlet, if you have a battery saver or a battery connected here, the ACC stuff stay on even if you power off the car.

Note the following diagram:
The FR power outlet fuse is unswitched (always on), the Power Outlet fuse is switched (only on in ACC).

 

Since the spell of really cold weather we've had, my Classic has shown signs that the 12V battery is getting weak (lights dim significantly when ignition is switched off, voltage at battery sags to below 11V within a few minutes of turning off the ignition, charging the battery in the vehicle didn't do anything to improve it).. It was still booting up the vehicle successfully, but with a whole winter ahead of us, I don't think it would have lasted much longer, so I decided to replace the battery (it's the original battery from its manufacture in 2000, so it's put in its time)..

I considered the Mazda battery, but it wasn't easily available (none ot the dealers had it in stock), so I ended up getting a sealed AGM battery meant for a Honda (the guy at the parts counter said it was for a Civic I beleive), which ws the same depth and just under 1/2" taller, but about 1.5" wider, and more importantly, it had the positive terminal on the right hand side like the Toyota battery vs. reversed for most other batteries.. Because it was longer, I had to remove and modify the sheet metal "tray" at the bottom of the battery compartment, but having done that, the battery fits in the space just fine.. I needed a slightly longer bolt for the hold-down strap (due to the extra height), but everything fit in place just fine... I replaced the terminals clamps with regular North American sized ones vs. cutting down the terminals. The new battery did not have a vent, but because the HV battery cooling duct also exhausts into the 12V battery space, and the new battery is an AGM vs. flooded, I'm not at all concerned about gas build-up.

When I got it out, I saw that the old battery case was bulged on either end, which suggests either gas build-up that didn't vent, or build-up at the plates due to sulfation.. I believe it's the latter as I hooked up the smart charger and it went into desulfation mode immediately, but errored out after several hours, indicating that it could not completely desulfate the battery.. The battery will still hold some charge, but its capacity is severely diminished.. I view the battery damage as confirmation of my contention the Prius' fixed 14V charge voltage represents a sub-optimal charging regimen...

 

The DC-DC converter is supposed to fall back to 13.8V when it detects the battery is charged.

 

That sounds like an almost perfect charging regimen. We live 'off the grid' and our house battery system is actually set to fully charge at 14.4 volts, fall back to 13.8 or so and charge away again. Of course in our cloudy Michigan winter, the poor things haven't seen either of those voltages for a while...

Jim

 

In living off the grid, what kind of set -up do you have? # of Batteries, type.....loads, etc. California is of course perfect for any type of solar, but the payback is never really sensible.