Say I add an aux 12V lifepo4 battery isolated with a battery isolator. Anybody got a clue how many amps is the Prius capable of, what's the power for charging the 12V batteries? I'm trying to figure out how fast I could charge a 100Ah lifepo4. PS: I have seen in this old thread that someone measured 1Kw - so 83 Amps. Looking for a confirmation. I know the main DC-DC inverter has a 100 Amp fuse. Is the charging capability directly related to that minus the needs for the car's system? Andrei
The Prius 12-volt system doesn't have any direct control over battery charging current. The DC/DC converter is rated 120 amps, and it produces a voltage sometimes closer to 13.6 V and sometimes more like 14.7. The car chooses those different output voltages in a kind of rudimentary scheme to control the charging of the factory-supplied 12 V battery, but of course all that really happens is that whatever current flows is just whatever that battery will draw when faced with 13.6 or 14.7 volts. The same will happen with your added battery, unless you add some extra circuitry to have more control.
So, in theory, accounting for the car's needs, the system could give something like 100 amps for charging? You think I should add a voltage regulator? From what I read, very loose research, 14.7V for charging is fine; and I immagine the Toyota engineers knew what they were doing. edit: Is there a way to dermine how much to limit the aux battery charging? I heard 3 numbers for that fuse: 100, 120, 125 amps. Whatever it is (and it matters) I'm not sure how to determine how much the car and the main 12V battery needs so the aux (lifepo4) charging would not draw too much and blow the fuse. From reading about those with inverters, I recall that 1000W is a "safe draw" ... but then again, correct me if I'm wrong. edit2: if I want to add an inverter, I suppose the proper/safe way would be to put it on the aux battery/ies?
The thing to keep in mind is that Toyota had no incentive to oversize the DC/DC converter. The 120 amp rating can be pretty much fully accounted for if you are using a lot of the electrical loads in the car (say, driving down a dark cold rainy road with the headlights and wipers and defoggers on and your seat heaters, and the engine isn't warmed up yet so the electric supplemental cabin heat is also on) and turning a tight corner at low speed with the electrical power steering. In fact, the converter has a special signal ("IDH") wired to the HVAC module for times when the converter needs to say "I'm overloaded, please 86 the supplemental heat for now." (That supplemental heat can be something like 700 watts all by itself.) On the other hand, there are times (a nice Sunday drive in fair weather) when plenty of the 120 amps are yours for your enjoyment. So if you're adding mods that can use a lot of power, it's partly about being aware of when you're asking for that power and when you're not. (I've now and then suggested, for people adding extra heavy loads, the idea of tapping into that IDH circuit, even just to light an LED or something so you see when the converter is saying Uncle!.
Did you save any "how to" on tapping into the IDH circuit? Can I read the amps drawn right at the fuse to get an idea of what is being drawn? Dogman says here that he's thinking about relocating this fuse. It crossed my mind, why not a 12V 120amp resettable fuse - a breaker - instead of these single use fuses? In a Prius reddit thread, someone said that the 120amp is reserved for the 12Vbattery alone - that would be cool, but like you said: Toyota definitely wasn't thinking "camper" when they made this car so I somehow doubt it. You sure the 120A is reserved for the entire car?
If you look at this guy's inverter setup, he added a 120 amp breaker for his inverter. But I suppose he's cooking while stationary - so the rest of the system is not drawing much power.
In gen 3, IDH is a blue wire from A59 pin 2 at the inverter/converter to L17 pin 27 at the A/C amplifier. On the way, it goes through pins 15 of AL1, a blue junction connector joining the engine bay wiring harness to the instrument panel harness. (AL1 is high under the dash on the left side, probably easy to access with the dash top removed, but otherwise probably the least convenient place to try to reach.) I think it is probably just a a level signal, perhaps normally 5 V or 12 V and signals by pulling to ground, or maybe it's normally at ground and signals by rising. I may once have thought that in a later generation it became a communication line of some sort, but I think I posted about that an Elektroingenieur talked me out of it, said it was still just a level signal. That thread might be around here somewhere. (Colors and pins above from a 2010 wiring diagram; if they changed in another year I wouldn't know that.)
Btw, what do you think if I added a 120amp 12V circuit breaker of this style ? Is there any downside to using something like that? I'm thinking, if I ever use too much power, it's as simple as flicking a switch instead of prying out that damn fuse and replacing it.
`@ChapmanF Looking through 3rd gen fuse diagrams and also like RJ mentions here, there is a fusible link in the engine compartment (125amp it seems, not 120amp - and this applies to V and C so I suppose regular Prius) and another fusible link at the battery (140amp). What could possible damage that 140amp rear fuse - called MAIN by Toyota? Excessively drawing from the 220V access points at the rear? What's the purpose of that fuse? That 140amp is for 201V? Seems like so many amps at that current. There's no 12V back there, right? You'll see why I ask - When people fry the 125amp fuse (that I called 120amp), it's the one in the engine compartment, right? It's almost never the 140amp one at the rear? I found this install review of 2kw AIMS inverter 240VDC to 110VAC with input 180-260V DC see post #16 (link to installation manual); so that seems simple enough (also dangerous). Some guy in a Prius fb group mentioned tapping to 300 amp straight into the main battery. Not sure what he's on, I asked, no answer so far. Probably typo, and he means 30amp 201VDC - knowing the battery is 6.6 kW from what I read. Correct me if I'm wrong: there are only 2 viable spots to draw from the Prius - the, so discussed, 12V DC converter line going to the 12V battery and the 201V DC point at the HV battery. Nothing else? The guy with his 300amps really made me scratch my head; and I wondered if things aren't more complicated than what I understand. Edit: I found your post: Electric power from a hybrid, connecting inverter to the high-voltage system I just found out from AIMS they don't make that 2kw converter anymore; I see you mention it too. Unbelievable. I want one (or two) BTW did you hear that Sienna/Highlanders have a DC 1500w inverter? I suppose adapting one of those to a Prius is not easy? +++++++++++++++++++++++++++++++++++++ I found this bluetooth smart shunt by Victron - there are ip65 models, lowest at 300amp ( Victron video, or Will Prowse video). If I put that inline on the negative between the 125amp Fusible and the converter, that should work to read the amps live right? Any idea what positive I could use to power it? Not that I have any idea what the wiring/space looks like down there atm; I have to watch some vids to get an idea Reminder for my Q above in case you missed it - what about replacing the fusible with OR at least putting in line a 12v 120 amp breaker which could be easily reset. Once I find out the amps drawn by the car. I plan to charge from the 12V line - through AC inverter - through 110V to 12V lifepo4 charger with variable amp (3 to 100V). I can only find a charger like that in 110AC. The variable amp would be to adjust from driving to stationary charging - when more amps would be available - the goal being to maximise the charging speed if needed. @rjparker @Patrick Wong @Elektroingenieur - I know you guys are also good with electronics, tagging in case you want to join this conversation.
A view of the 125amp fuse, posted by RJ in the 8th post here: That makes me think the 12v 120amp (or 125amp if I can find one) breaker idea is viable. Let me know if you think this is a bad idea in any way. Example of a 12v 125amp breaker.
Just a thought. Many times circuit breakers do not trip as quickly as fuses blow. That time difference could be an issue.
