[ps2fixer]

Oh just had an interesting idea.... The 12v battery was dead on this prius when I got it. It seems to be slow to charge, and fairly quick to discharge, so I'm thinking it might not be too healthy anyway. There are small atv batteries that are lithium ion based with a built in BMS. Of my understanding, the prius doesn't need much for amps for the 12v system to function correctly. I haven't seen any real world numbers.... but I do have a scope that could read it. I just haven't gotten my laptop up and running with the software/drivers yet. I think worst case would be with HVAC on high, headlights on, and brake lights on. Besides the car doing some 12v based stuff with the key off, it doesn't seem to need much capacity or amps. I'd assume 100 amps peak output should be plenty. As long as the car isn't used in accessory mode much, and the interior lights aren't left on, there shouldn't be much of a need for any real capacity. Just put the car in ready mode and draw off the hybrid battery.

Talking about batteries and all of that, it seems like car computers and radios would start using eeproms more for their "memory". Chips exist that have millions of write cycles for their spec, if that's not enough, over size the memory and cycle across all sections similar to how an SSD works under the hood. There really is no reason a car needs 12v power all the time besides the antenna for the key fob and the security to monitor door switches, both features I could live without but I prefer 90's era cars lol.

I don't have an exact figure, but somewhere around 4-5 hours the interior light was left on, it wasn't dead, but the battery voltage was down below 12v, I think it was 11.9v on the scan gauge. Quick search shows they are about 10w, for easy math let's say 1 amp of draw, that's about 5ah battery capacity. Based on a google search, AGM batteries lower limit is 11.6v for fully discharged. Looks like the battery that's in the car is rated at 38ah.

Clearly I need to switch the main interior lights over to LED as well, just to prevent issues drawing the battery low. Looks like they are 1w or less, which means 10+ hours would be 1ah of drain, or to give the same situation above, it would take 40-50 hours for the same draw on the battery. The actual fuel savings for the lower power use is effectively 0mpg, so that's not the root reason to change them out.

Once the battery is fully charged again, I'll have to throw my battery amp tester on it and see what it shows. I think the battery is 450cca rated even though the prius doesn't need anywhere near that much amperage.

Side benefit from the lithium ion battery should be that the charging draw should drop to effectively 0w once fully charged and the charge/discharge efficiency should be much better compared to agm/lead acid. Maybe this is one of the sources of pulling my mpg down a bit. Even at 10 amp charge (120w) I wouldn't think it would make that huge of an effect of mpg. Just sitting with the car in ready mode, the hybrid battery has 400w+ coming off it and the state of charge doesn't seem to get effected by that much at all.

Talking about state of charge, if I take the corner a bit faster onto my dirt road I've lowered the SOC drain on the hybrid battery to about 0.5%. Getting back to the corner purely on electric power takes around 13% at 20mph for roughly a 1/4 mile slightly up hill, that figure came from a rainy day too so muddy road likely didn't help at all.

It didn't seem like too many people talked about the prius's design much when searching around, but it seems like the computer is smart enough to *not* recharge the hybrid battery when the engine is cold. Earlier today when I left, I got the battery down to around 54%. After the initial take off I remember seeing 57% and I kept an eye on it for half a mile or so while it was in cold start yet (under 120F) and I didn't notice it coming up. I wasn't watching it super close though, by the time i got to the post office, I was around 59 or 60 like normal.

For take off, it seems targeting around 2000-2100rpm isn't a bad figure. It seems like it doesn't use much or any energy from the hybrid battery for take off which means all of the energy is from the engine (less round trip efficiency loss). I have to give it quite a lot of throttle at first (little more than enough to kick the engine on in EV mode) and have to let off as the speed increases. I'll have to try some other rpm targets or other ways of measuring take off to see if I can find a better target to go with.

Maybe I'm missing something, but it seems like going around 40mph the excess energy from the engine goes into the battery and it charges it up and eventually does the engine off EV only route. If I go 45mph, it seems to not charge the battery and lower the engine rpm instead. In my mind, I would think keeping the engine at the higher load and pushing the excess energy into the battery, then idling the engine and using electric assist to burn it up would be more efficient, kind of like a pulse and glide but based on engine load, really similar to the under 42mph logic. I suspect that's why at that speed limit there's such a drop in mpg in the prius speed vs mpg chart.

Increasing the mph limit for EV mode to 45mph (ideally 46-47mph) would probably make me see quite a huge mpg gain. I could slow down to 40mph, but I'm trying to not be a thorn in everyone's side.

I wonder what's the difference for the newer prius that can run into the 80mph range in EV mode. I know my car's max hp out in EV mode isn't huge, but it could do 45mph I'm sure, I suspect I could get my current 45mph mpg figures at 55mph if it was able to run in ev mode at those speeds.

Anyway, I have some ideas fumbling around in my head on things, once I catch up on things, I'll have to look into the ideas and see if I can find a net gain on making the engine warm up faster with out going crazy on hacking things up lol.