Solar panel battery charging experiment

[EcoCivic]

Originally Posted by ttrainxl

Hopefully I’m wrong, but I’d be surprised if my ‘95 Civic completely cuts fuel when decelerating in gear. If that were the case, it seems shifting to neutral to coast wouldn’t be as effective. I know you coast much further if not in gear, but to fire all cylinders while coasting versus not firing any cylinders in gear, even if you don’t coast nearly as long, it seems coasting in neutral would t have as much advantage as it proves to have.

Maybe decel fuel cut is a thing for late model cars, say from 2015 or 2017 and on, but for mid 90s vehicles, even though fuel injection had been in play for ten years, seems unlikely to me.

I hope I’m wrong.

1995 is new enough that I would expect it to have decel fuel cutoff, but I have no experience with the 5th gen Civics so I can't say for sure. But there are easy ways to find out for sure if you can't feel it.

Is it manual or automatic? If it's manual, with the engine fully warmed up, release the throttle for at least a few seconds while in gear at around 2000 RPM or more and then carefully shut off the key one click for a couple seconds and see if the sound of the engine changes or engine braking increases with the key off. If there is no difference, it's definitely in fuel cut.

With an automatic, that test won't be reliable because the transmission has electronic controls. Instead, temporarily install a small LED in parallel with one of the fuel injectors by backprobing one of the injector plugs or the pins at the ECU and put it somewhere you can see it. If it turns off when you release the throttle while in gear and well above idle, there is no fuel being injected.

[ttrainxl]

Originally Posted by EcoCivic

1995 is new enough that I would expect it to have decel fuel cutoff, but I have no experience with the 5th gen Civics so I can't say for sure. But there are easy ways to find out for sure if you can't feel it.

Is it manual or automatic? If it's manual, with the engine fully warmed up, release the throttle for at least a few seconds while in gear at around 2000 RPM or more and then carefully shut off the key one click for a couple seconds and see if the sound of the engine changes or engine braking increases with the key off. If there is no difference, it's definitely in fuel cut.

With an automatic, that test won't be reliable because the transmission has electronic controls. Instead, temporarily install a small LED in parallel with one of the fuel injectors by backprobing one of the injector plugs or the pins at the ECU and put it somewhere you can see it. If it turns off when you release the throttle while in gear and well above idle, there is no fuel being injected.

Transmission is manual. I’ll have to try that but I’m out of town until the end of the month and without the car. Good to know. Thanks!

[serialk11r]

AFAIK the cost of cycling the battery is a lot higher than the cost of running the alternator, so that panel better be supplying the full electrical needs of the car, which is a tall order.

[EcoCivic]

I may have found a way to automate regen. In Kmanager, there's an option for a universal output with engine speed, vehicle speed, engine load, and throttle position parameters and I would think I could achieve what I want with those. I'm thinking I'll start by setting the output to activate when vehicle speed is 5+ MPH, engine speed is 1100+ RPM, and throttle position is 0%. I'm thinking that should probably work, but I'll have to verify with a light first.

As for how much energy can be recovered by the alternator, it's not as much as I would have thought. As a best case scenario, if the battery is discharged deeply enough to continuously accept the alternator's rated 105 amps for 30 seconds of engine braking, I could recover around 0.875 amp hours or a tad over 1% of my battery's capacity. At most, that would replenish about 6 minutes of range. Sounds good since 6 minutes is a significant percentage of most trips, but since the battery would normally accept only a fraction of that current, the actual energy recovery would be much less.

[freebeard]

As for how much energy can be recovered by the alternator, it's not as much as I would have thought.

I am not surprised. What I had in mind at #13 was the thread on the eAssist altermotor. It has 15HP bidirectional and a serpentine belt system.

[serialk11r]

Your car uses that little? I've measured mine at >20 A key on (the only ammeter I have is meant for high current so it could be off by a few amps). I've measured about 120A charging for my 40Ah lithium titanate battery, so each second braking only powers the electronics for 5 seconds, probably less since I don't think the alternator output is that high, I'm guessing it's 130A. Some newer cars have 180-200A alternators which would do a little better but it's still not that much.

Basically a good reason to use higher voltage electrical systems. Actually, speaking of that, maybe you could? If you're running off battery + solar, you could double up on the battery, then double the alternator voltage, and then run the car off a DC converter.

[EcoCivic]

Originally Posted by serialk11r

Your car uses that little? I've measured mine at >20 A key on (the only ammeter I have is meant for high current so it could be off by a few amps). I've measured about 120A charging for my 40Ah lithium titanate battery, so each second braking only powers the electronics for 5 seconds, probably less since I don't think the alternator output is that high, I'm guessing it's 130A. Some newer cars have 180-200A alternators which would do a little better but it's still not that much.

Basically a good reason to use higher voltage electrical systems. Actually, speaking of that, maybe you could? If you're running off battery + solar, you could double up on the battery, then double the alternator voltage, and then run the car off a DC converter.

Yup, it only uses around 8 amps with the engine idling and no accessories on according to my Klein amp clamp which seems reasonably accurate. By far the largest load is the fuel pump at about 5 amps and the remaining 3 amps are going to the ECU, sensors, ignition, gauge cluster, etc. However, with the key on and engine off, my alternator draws about 8 amps through the large positive cable, so perhaps that has something to do with why your consumption seems so high?

A higher voltage system would be cool and definitely has efficiency benefits, but I don't think the benefits would be worth converting just for slightly lower power losses through the wiring over just using larger wiring. A AC-DC converter would also introduce efficiency losses and points of failure.

I have wondered about the optimal voltage for my solar array as I add panels in the future though. My charge controller supports up to a 100 volt input and a higher voltage would decrease current, but my understanding is that charge controllers becomes less efficient the more they have to step down the voltage.

[Blacktree]

One note about DFCO: there is often a delay before it is activated. The delay could be several seconds, which would severely reduce its effectiveness for fuel economy. Although you may be able to adjust that in the ECU programming.

[EcoCivic]

Originally Posted by Blacktree

One note about DFCO: there is often a delay before it is activated. The delay could be several seconds, which would severely reduce its effectiveness for fuel economy. Although you may be able to adjust that in the ECU programming.

Good point. I have read that tapping the brake pedal enough to activate the brake lights can quickly activate DFCO on some cars since the brake light switch is usually an input to the ECU, but all my cars fortunately go into fuel cut almost instantly.

[EcoCivic]

Apparently decel fuel cutoff goes back quite a long way. I just checked my 1996-1998 Civic service manual since that's the oldest one I have access to at the moment and here's what it says about decel fuel cutoff:

"3. Fuel Cut-off Control
. During deceleration with the throttle valve closed, current to the fuel injectors is cut off to improve fuel economy at
speeds over the {ollowing rpm:
. D16Y5 engine (M/T): 850 rpm
. D16Y5 engine lCVT), D16Y8 engine (USA M/T)r 920 rpm
' D16Y8 engine (USA A,/T), Dl6Y7 ensine (USA A"/T):910 rpm
. D16Y8 engine (Canada M//T), Dl6Y7 engine (Canada):990 rpm
. D'16Y8 engine (Canada M/T): 1,000 rpm
. Fuel cut-off action also takes place when engine speed exceeds 6,900 rpm (D16Y5, Dl6Y7 engine; D16Y8 engine:
7,000 rpm), regardless of the position of the throttle valve, to protect the engine from over-revving."