Charging up a trailer battery with our Gen 3?

If you do so in READY, there will be no drain on the 12 volt battery.

 

i wouldn't attempt it, but if you do everything right, it won't damage anything.

biggest problem is the prius inverter makes for a poor charging system. it's designed to maintain more than charge.
if the trailer battery isn't too big, it might charge it over a few days with the car left in ready.

 

I would expect a matter of hours, rather than days, just as for the battery that is in the car.

The DC/DC converter in the car outputs a regulated voltage, not a limited current. The battery will charge at a rate that reflects the voltage and, inversely, the battery's own state of charge. Other things being equal, a 'larger' battery will draw a larger charging current at the same voltage and charge state, so the 'size' of the trailer battery isn't likely to have a large effect on the time required. It would need to be crazy big before the time would depend on the converter's output current limit, which is over 100 amps.

Gen 1 and Gen 2 had a lower converter output voltage, which led to lower charging currents where a full charge of a depleted battery would need 15 hours or more left in READY. At the higher charging voltages introduced in Gen 3, it doesn't take that long.

 

First, I assume the house trailer has a single 12v battery with an onboard 120v battery charger. If that is the case, the only way I would attempt to charge the trailer battery is through its own charger.

To do that with a Prius, you will need a 12v to 120v inverter plugged into the Prius 12v power outlet. The inverter needs to have a maximum 12v input current of 10 amps or 120 watts. The car would have to be in Ready, eg running. At that point you could plug the trailer into the inverter's 120v output. You can not run your trailer's 120v ac, refrigerator, microwave or heater if equipped. You should be able to charge the trailer's 12v battery.

There are alternate "hacks" such as attempting to jump the Prius 12v battery to the trailer 12v battery. Do not do it! It is too easy to damage your car with a one second bad connection to the point where the car won't run. However this hack can provide fast charging and may be suggested. It is safer on conventional cars than on a Prius.

Another option would use a fairly large solar panel setup with a charge controller to feed the trailers 12v.

 

Probably not but........
IF the battery in the trailer is big enough and low enough on charge, it might indeed draw some from the Prius battery because the charging system is not very "robust".
AND.....if you screw up the connections, you could damage/disable your car too.

Doesn't Toyota still recommend that you NOT use a Prius to "jump" another vehicle ?
That is really what the trailer connection amounts to.

 

Not knowing the configuration of the trailers power source (battery and/or electrical system) it's difficult to make assumptions about how the Prius would be used to "top off the trailers system/battery"

There is a fairly large contingent of Gen3 owners that added all kinds of inverters to there Pri for all kinds of uses. rjparker mentioned one above in the second paragraph of post #5. There are plenty more of all different shapes, sizes and connected to either the 12 volt or the traction pack.

 

Every time I read about the charging system in the Prius not being very "robust", I think "compared to what?"

The DC/DC converter in a Gen 3 is rated 120 amps. If you had another car with a 120 amp alternator, that'd probably be probably an aftermarket high-output alternator that you added as a mod.

According to that same link, "[m]ost factory alternators are rated at 65 to 100 amps". I would guess that in modern vehicles one isn't seeing as many down at the 65 end anymore (that was typical when I was younger), but I still don't see much reason to talk of 120 amps as if it's wimpy.

 

Many people believe the 12v charging is constrained to 4.2 amps because of the manual's charger caution and the "limit" on the factory battery sticker. Of course that has nothing to do with the hybrids system's capabilities or observed charging rates. Toyota was trying to prevent an old school 100 amp shop charger from being left on overnight and ruining the battery.

 

when people buy a new battery that has been sitting on the shelf and is measuring around 12 volts, then they install it and drive it for a few weeks, then the car won't start one day, it makes me wonder how much charge the car is giving it.
we have seen this scenario repeated in one form or another for almost 20 years

 

Pretty much everything that happens in physics has an explanation. That's what I like about it.

It's just that the real explanation isn't always found until people get serious about making measurements and excluding the speculations that don't fit what's already known about the system.