Low Voltage in Rear Power Outlet

I think I'd be expecting collateral damage. LOL!

 

Sometimes lead acid batteries “violently decompose” when shorted across the terminals. You do not want to be there when it happens. They make the Samsung phones look like a lit match.

 

I do a lot of work on CRT's (I collect and restore old 80's era arcade games). When you do that, however you have to worry about the tube itself retaining some high voltage charge (19K is usually at the lowest), even if the monitor has been off for a while (days) they still maintain more than enough charge to shock the crap out of you. (it's not so much that the current's going to kill you, but arm instantly contracting at full force and smacking into the side of the arcade cabinet hurts like a mofo).

To get around this I keep a screw driver handy with a 1 meg ohm resistor connected from it to an alligator clamp. I attach the clamp to frame ground, sneak the screwdriver under the 2nd anode and safely drain any latent charge to ground.

so the point of this is just use a resistor in series, don't use a wrench!

(as an aside, I've seen crt's hold charge for over a month. I had a robotron 2084 that needed a new flyback. I figured it was sitting there for long enough that it surely would have self-discharged by now. So I grabbed the 2nd anode and wham... boy that hurt!. So, I then figure, ok, SURELY it had to have been discharged now. grab it again... wham. F**K! ok... NOW it must be discharged. yup. you guessed it. on the 4th try I walked to my workroom (I was doing the fly replacement in place rather than dragging the cabinet into the workshop) and got the discharge tool). BTW, if you really want to see a tv explode (e.g. remove the metal retaining ring around the tube and hit it with a rifle shot), you need to make sure you charge up the tube nicely first! Remove the 2nd anode, let the electron gun load up the tube like crazy and then shoot it.

 

I have experienced a lead acid battery explosion, sounds like a shot gun going off.

 

Whats going on with your battery voltage?

 

I don’t know, either, but I also can’t find anything in Toyota’s published information that says 12.6 volts is unacceptable. New Car Features (more info) says the “Rated Output Voltage” of the DC-DC converter is 11.0 to 15.0 volts, but it describes the charging control strategy for the auxiliary battery only in general terms, without enough information to determine what the voltage should be under specific conditions.

If the auxiliary battery has failed a test with a Toyota-approved diagnostic charger (such as the Midtronics GR8, mentioned in a previous thread, where I also described Toyota’s warranty policy for batteries), and the car is in warranty, the battery should be replaced. It’s disappointing to read otherwise (post #75); nothing in the warranty terms says a vehicle has to be disabled before Toyota is required to correct defects, especially if the part has been found to be defective according to Toyota’s own standard test method.

If the battery passes the test, or if the trouble continues after it’s replaced, I’d suggest returning to the diagnostic steps I outlined in post #18. The car should at least be able to pass the on-vehicle inspection for the charging system, done step-by-step, exactly as stated in the Repair Manual.

@ChapmanF's suggestion in post #66 to investigate the power outlet wiring is also a good one; a voltage drop check is easy enough to do. Toyota dealers are also required to have a milliohmmeter, as an essential tool (11413-00005, a Hioki RM3548), though yours may not have anyone who knows how to use it.

You may find it helpful to know that the sales brochure (PDF) says the car has “One front and one rear 12V auxiliary power outlets,” and the Owner’s Manual (PDF) says of the outlets, on page 532, “Please use as a power supply for electronic goods that use less than 12 V DC/10 A (power consumption of 120 W).” The brochure and manual have many disclaimers, but they might still help establish your reasonable expectation that the car’s electrical system would be able to provide that voltage and current at the outlets.

 

I wonder if the voltage drop you're seeing at the outlets is all due to wire gauge (requiring a total rewire of the circuit), or could be traceable to a dodgy connection somewhere?

 

That thought crossed my mind, too—but I’m not sure what single faulty connection, other than the + or – terminals of the auxiliary battery, or perhaps at the battery state sensor assembly, could account for low voltage at both power outlets and at the radio head unit.

The Electrical Wiring Diagram shows that the No. 1 (front) and No. 2 (rear) power outlets have separate supply connections. No. 1 is fed from the P/OUTLET NO.1 fuse in the Instrument Panel Junction Block Assembly, and No. 2 is fed, via a relay, from the P/OUTLET NO.2 fuse in Unit B of Engine Room Junction Block No. 1. The first point in common is inside the fusible link block assembly at the positive terminal of the battery. Both paths go through connector 3A, but they are on separate wires and terminals.

Both outlets are wired to ground point ID behind the right side of the instrument panel. A bad connection there wouldn’t explain low voltage at the head unit, though, since it’s connected instead to ground point IB, under the center of the instrument panel.

 

I was just going to ask whether your dropped measurements are at the power jacks where the Toyota wire reaches them, or on your side of your plugged-in accessory plugs. Your question may have just answered my question.

Those accessory cig lighter plugs are not always, hmm, instrument quality....

Much of the interior trim in a Prius comes off just by pulling on it, but a quick look in the repair manual can boost your confidence that you know the right places to pull.

 

I agree that Toyota is unlikely to have used undersized wires: since the power outlet fuses are rated at 15 amperes, I’d expect the design engineer to have selected a wire that could safely carry at least that much current, at the highest ambient temperature expected inside the car.

In making your estimate, did you consider the wire sizes? The wires between the battery (fusible link block assembly) and junction blocks are of much larger sizes than the wires from the junction block to the power outlets, or from the power outlets to the ground point. The resistance of these larger wires, per unit length, is lower, since DC resistance varies inversely with the cross-sectional area of the conductor, approximated by R = ρ ℓ  ∕ A, in which ρ is the volume resistivity, 1.7241×10⁻⁸ Ω·m for annealed copper at 20 °C.

For an example of this in practice, see the Sumitomo Wiring Systems catalog page for AVS wire, which tabulates the resistance, in milliohms per meter, for various nominal wire sizes, given in mm². Toyota may have used another style of wire, but the table shows how the principle applies.

That said, 0.8 V may not be too far off: if the balance of the circuit uses 1.25 mm² wire, for example, the voltage drop for a 10 ampere load could be something like: 20 feet × 14.3 mΩ/m × 10 A ≈ 0.87 V.

As @ChapmanF kindly suggests, the Repair Manual is the best source. If you have a Los Angeles Public Library card, the Chilton Library service, under 2016 Toyota Prius > Repair > Body Interior > Interior Panels / Trim > Rear Console Box, gives installation and removal procedures identical to those in the Repair Manual for the Prius Prime. Pages 6 and 7 of the Accessory Installation Manual for the wireless hotspot sold for the Prius PHV in Europe also show how the center console comes apart.

If you’re not familiar with the connectors, see the Electronic Circuit Inspection Procedure in the Repair Manual, or the older Wire Harness Repair Manual (PDF). One important point: don’t deform the terminals by inserting multimeter probes into the front of a disconnected connector. Instead, probe carefully from the back (wire) side with pins, Toyota 09082-1C141, Kaise 792, Fluke TP40, or similar.

 

Backprobes also let you make the measurement without the connector disconnected, so you can measure while your load is applied.

 

hey, quick though... have you tried making a quick harness that parallels both the console 12V and the rear (bottom in back, middle) 12V outlet? that is, hook BOTH of them up in parallel to see if that will overcome the voltage drop you're seeing? Not a perfect solution by far but it may allow your inverter to run until Toyota get's their act into gear.