At Burning man as well as local festivals our camp uses a bank of 8 deep cycle batteries hooked to an inverter to run our stereo, lights, etc. We are able to get an heavy evening of use out of the battery bank. If we add our solar panels we can get two evenings of use then it has to be charged by a very loud and annoying gas generator. I had the idea to hook this battery bank into my Prius V 12v system and let the Prius "idle" in "ready mode". I know some people have run 1kw inverters in emergencies to keep their fridge running. My concern is how could I limit the draw from my battery bank so I do not overload the system that supplied power to the 12v system from the high voltage pack. Somebody told me I want a "battery isolator". Any ideas?
So it sounds like you want to draw off the external battery bank at the same time as you are charging the external battery bank?
Battery isolators are not the answer, they simply drop out the load before the rv’s battery is discharged. Paralleling deep cycle batteries to your Prius battery is also a bad idea because of different charge/discharge profiles which creates different voltages between the paralleled batteries. That leads to massive battery to battery currents, typically ruining the batteries. You may need a separate quality charger for your battery bank that runs off the Prius 12v. Most agree that a 1kw external inverter is the maximum that the Prius inverter/converter could keep up with in ready mode. That would require a fused direct connection to the Prius 12v battery. Expect maybe 80% efficiency and realize you are dealing with high amps, possibly 100 amps to get the 1kw at capacity. Wire size is important. I would try to find a dc to dc charger, max size 1kw. My main concern would be the long term health of the Prius inverter/converter used in this way when there would be less consequences with a low noise Honda generator. Plus possible Prius engine issues like cooling failures that went unnoticed because there was no driver at the wheel. Personally, I would limit this type of Prius 12v use to home emergencies like post hurricane or similar. Even then I would much prefer a propane generator and tank since propane will keep for decades.
why not just use a massive inverter hooked up to your hybrid battery, and let the v do what it does best?
It would seem one at a time would be better. DC/DC battery chargers, 12 volt heavy duty industrial, DC Input Battery Charger for Lead Acid and SLA Batteries, for charging 12V batteries in 12V, 13.8V, and 14.4V vehicles They make larger units in case you were brave enough to charge 8 at a time. 12V to 12V DC-DC battery charger, 600 Watt 12 volt to 12 volt DC DC battery charger, Heavy duty and military grade 12VDC to 12VDC DC-input lead acid battery chargers 50A amp charge rate from PowerStream. This is going to be very near the limit (one way or the other) of the Prius charging circuit!
I've got an off-grid vacation property that is similar (electrically anyway) to what benstpierre is doing. I agree with bisco, a high-voltage inverter would be the most elegant solution, but they're hard to find and expensive. Failing that the next best would be a ~1kw inverter on the prius 12v system to power a battery charger. That battery charger will serve to limit the current delivered to the deep cycle battery bank. I use a Samlex charger to recharge my deep-cycle batteries from a generator when our loads are higher than what we can recover from our solar panels. Good equipment. Just to mention it, one thing that helped us a lot was to use a large, powerful battery charger on our setup. The idea is to hit the generator for all it is worth in the interests of shortening the actual run-time. Even when we had our solar cells offline for maintenance we only needed about 90 minutes of run-time to put 24h worth of charge into the deep cycle string. A charger should always be sized in proportion to the batteries it feeds, so make sure you stay in a safe range.
Please try and forgive ignorance of the part names, as I'm just looking into this myself and new to Prius. My understanding is there is a traction battery high voltage to 12V converter in every Prius/Volt/Leaf(likely others), that maintains the 12v battery; It seems that the converter is rated around 100amps in most... When the car is "on" or ready mode, the traction battery will maintain 14.0v to the 12v battery until the traction is depleted, then the engine will automatically start and charge the traction again(while it continues to maintain the 12V) and the process will continue until car runs out of gas. My concern is what sort of amperage/current control does the converter have? If there is one built-in or if it's just counting on the resistance of the small battery and monitoring voltage? If there is a 'smart'/safe current limiter on the controller, it would simply be safe to divert the 12V feed from the 12V internal battery to the external 12V(presuming) bank.. A large 12v bank's main issue would be that when discharged it could 'take' over 100 amps for some time, risking blowing out the cars converter... If there is a current limiter in the converter(and there might well be, in a typical alternator that's just a limitation of output), I could see using a prius as a valid emergency generator for a larger 12v bank. If there isn't a current limiter, and you knew before your external bank was going to be discharged(ie: while it was already charged), you could divert the 12V feed from the car and it would 'maintain' the bank(so long as there wasn't any persistent > 100amp draws.
