Hey guys, Even with regular cars these days, the alternator doesn't always output ~14.2V but sometimes more like 12.5 volts when the amount of accessories running is low, or if the charging system is smart, if it sees that the battery is well charged + not many accessories running. So often times during the day you could plug in a cigarette lighter volt meter in and see it only at 12.5V or so but when you turn the blower motor on full and the headlights, the voltage stays at ~14-14.2V. The reasoning is to save fuel if the lead acid battery is charged/not a high load. I believe this behavior is similar for most or all new conventional cars out there. The algorithm often also has to do with engine temp and MPH. This is how it is with my '99 Civic. You can take out the current-meter device that the computer sees and then the alternator will always try to keep battery voltage at ~14.2V constantly. Useful for keeping the battery happy. Has anyone monitored the logic of charging the lead acid battery on the Prius and if the 2nd and 3rd gen is different? Does the Prius not keep the lead acid battery very charged and causes sulfation. I've heard some people have installed float chargers or trickle chargers to top off the lead acid battery for some reason in their Prius. Hacks to keep the DC-14VDC converter active all the time the car is on? Thanks. Oh, and does anyone know if this converter is protected from overheating and is water cooled?
In My Gen 2 Prius, I saw an almost constant 13.8 or 13.7, in my v 14.4 or 14.5. I suspect the Gen 3 cars do not have as long to charge as the Gen 2s did.
Having done some recent experiments, that are ongoing on the gen2 Prius I can state that the highest charge voltage I have registered so far is 14.7 volts at 43 amps. I have no doubt it is capable of higher rates than this. The charge rate drops as the battery is near full charge to about 13.8 volts. This is rather strange considering the OEM battery clearly states on it's top label "maximum charge rate 4 amps" and possibly one of the reasons it does not seem to handle deep discharge well. Not having a gen3 I cannot say how the charging system reacts to a partially discharged battery, but considering it is temperature monitored I would think it too has a possible high charge rate. The DC to DC converter is capable of circa 100 amps. John (Britprius)
So the Prius doesn't ever or hardly ever go into a power saving mode in which the voltage at the lead acid battery drops below 13V? That is very good, should keep the lead acid battery nearly fully charged or fully charged then as long as you drive (or turn the car on) at least a few times a week. Is that DC converter water cooled like the traction motor converters? Thanks
Yes, I think so. - underlining by me Special Issue: Inside the Toyota Prius: Part 5 - Inverter/converter is Prius' power broker
Hi John, Andrew again in Nova Scotia. Related to this topic and our previous conversations, how have you wired your caravan battery to your Prius? I know you are Gen 2, but it might be the same for Gen 3. I would like to be capable of a decent charge from the car but only want the trailer connected when the car is in "ready" mode so I don't stress the little Prius battery. I was thinking of tapping into one of the 12v outlets back to a high load relay located back near the battery. Since our standard trailer plugs only go to 10 gauge, I was even wondering about using a separate high current battery plug for any time that I am camping without services. Any advice or shared experience would be appreciated. Thanks, Andrew
