non-starting 2006 Prius--12V?

Hi from a UK Hybid Import Newbie!
Just a point of interest for all of you "non-commercia"l motorists out there this winter:
12V batteries contain water
When discharged through use of fans, heaters, lights etc. the battery "Acid" is mainly water
Water freezes in cold temperatures, fracturing plates and connectors
Intermittently from that time the connections will make and break

Charge up your battery by giving it a good(20-30 mile) run
Do not leave any unnecessary electrics running when charging is off
If battery discharges when left unused for a week - only alarm/clock/radio memory/imobilizer/ECU's drawing power - Replace it!

Hope this helps, 35 years experience as a Commercial Driver!
Norrie.

 

I am wondering why you felt the need to put the 10 ohm resistor in series with your jumper pack? Why not instead use one of your Fluke meters to read the current flow?

The quiescent current flow when the car is IG-OFF will be around 20 mA and will pulse up and down as the security LED turns on and off.

I am not aware of any relay that disconnects the dedicated positive jump start terminal. Use your Fluke meter to measure voltage at that terminal, to ground.

It is not necessary to drive the Prius in order to charge up the 12V battery, as the 12V bus voltage when READY remains the same (~13.8V) whether your speed is 0 mph or 100 mph. Also, 20-30 miles implies driving time of 30 minutes to one hour at most. That is not sufficient time to charge up the 12V battery at a charging voltage of 13.8V; overnight is more like it.

 

Having left my Prius for a week without driving, in (for Britain) very cold weather, I found it producing the warning triangle on every start. It was also randomly setting off its alarm (standard fit in the UK). This was three weeks after a previous week without driving. The 12V battery was down to 9.4V in Accessories mode with all lights etc turned off, according to the Vehicle Signal Check screen. The MFD will allow its input voltage to go down to about 8.4V before it switches itself off - that was the lowest I saw when going from ACC to IG-ON mode.

I did note that the area of the roof above the map light assembly had a different colour/pattern of frost to the rest of the roof, possibly indicating that it was warmer, possibly indicating a short. I've flicked the switches a few times to ensure it's not an intermittent contact, and the frost pattern was uniform the last few nights.

Down at this level, I noted that the charge voltage was 13.8V. I left it on for 8 hours and it had increased to 13.9V.

With further driving (minimum 30 minutes commute each day) this had risen to 14.0V, and after sitting overnight the battery was now at about 12.0V in ACC mode.

I recall seeing charging voltage as high as 14.4V when the battery was healthier.

It's my belief that Toyota have implemented a charging algorithm similar to this:



(source: Charging the lead-acid battery)

2.2V per cell is 13.2V for a six-cell battery, the constant voltage phase voltage of 2.4V/cell would be 14.4V and the float voltage of 2.25V would be 13.5V.

The charging current recommended by Yuasa for the OEM battery is 2 amps, for the smaller battery used in non-smart-key cars such as mine. This has a nominal 35Ah capacity - at a rate of 2A it will take over 17 hours to fully recharge. The larger battery for smart-key cars (also used in the UK for cars with fog lamps) can accept 3A and has a 46Ah capacity, but I don't know if the Prius charges it this fast. I would assume not.

If your car is showing 13.8V when READY, it means one of two things: it's either very nearly full (so don't worry), or it's very nearly flat and will require a very long time to recharge. Check it in ACC mode before making the car READY to see which it is.

 

Re: if no relay, then I erred

I'm with you on this one. In these situations I use a clamp-on ammeter to avoid nasty surprises.

Tom

 

Re: if no relay, then I erred

12.60V is perfectly normal for a brand new battery that has sat in the car overnight. The battery is always under parasitic load, 10s of mA. 12.90V represents 100% SoC with no load. Now that you have an Optima, it should give you years of trouble-free operation. If you are really worried about higher than normal current drain, get a cheapie DMM (i.e. Harbor Freight freebie) and connect it in series with your HF battery pack at the engine compartment jump point. Then disconnect your Optima. Read the current under the hood, and the voltage in the trunk. If the current is higher than 100ma and steady (assuming all doors are closed), then you may have a problem somewhere.

 

Re: if no relay, then I erred

I think that 12.6V when IG-OFF is OK considering that the quiescent current draw is ~20 mA.

Good point about the resistor. However a 10 ohm resistor will limit maximum current flow to ~1.2A. If you open a door and the cabin lights come on or the brake accumulator pump runs, this amount of current will not be sufficient.

This is why I don't think using a jump pack is the best solution if your intent is merely to keep the ECUs alive. I use a lab power supply where the maximum current available is 3A, which won't cause too much damage.