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Thread: Alternator delete with regen braking modification for better MPG

  1. #1
    Administrator Daox's Avatar
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    Alternator delete with regen braking modification for better MPG

    So, now that I am commuting again, I am motivated to do some more fun stuff with the Mirage. The next mod I am currently planning an alternator delete.

    What is an alternator delete? Well, in this case it simply means I am going to disable (not actually delete) my alternator electrically. This will stop it from putting a load on the engine. The effect is increases fuel economy (a very impressive 5-10% on some cars) and also increases available power to the wheels. However, the battery still needs to be charged, so you do that with a battery charger. Just plug it in when you get home, and its ready when you want to leave.

    I already started preparing for this mod when I put a deep cycle battery in the Mirage when I accidentally killed the original battery (oops). You need a deep cycle battery so you can run the car off the battery. A normal OEM starting type battery does not have the necessary capacity, and also starting batteries die a quick death if deeply cycled. So, the only additional thing that I need to do is install a switch inline with the field regulator control wire. This will stop the alternator from charging the battery. Also, if you want to charge the battery with the alternator, all you do is flick the switch and it turns back on. This comes in very handy if you go on a long trip.

    But, what about REGEN BRAKING??? That will be phase two of the modification. I will be doing that later on, but I'll outline what it'll do because it is pretty cool. Since we installed a switch to turn the alternator on and off at will, we can use that switch (or much more likely a relay or mosfet) to turn the alternator back on while braking. We can use the brake lights turning on as a trigger for that relay, so whenever your brake lights turn on, it turns the alternator on. I will probably use an arduino to control the setup because I like it, and it gives me more control and options for future mods. An arduino is a programmable micro controller for those who don't know, essentially a tiny computer that can do tons of different things. It will help if I ever get to phase three of this modification.

    Phase three is essentially beefing up the regen capability of the alternator. By sending a false battery voltage signal to the alternator, whenever the regenerative braking comes on, I can max out the alternator output. This essentially just makes the setup work a little better than normal. Testing will need to be done to see if this is actually necessary, and I may never get to this phase. But, I'm laying it out here because it is being planned for.


    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar, Upper grill block

    Current project: Alternator delete with regen braking modification

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 45.7 mpg (US) ... 19.4 km/L ... 5.1 L/100 km ... 54.9 mpg (Imp)


  2. #2
    Still Plays With Cars Loren's Avatar
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    The stock alternator is already controlled by the ECU. It switches it "on" when it is needed, and "off" when it is not needed, or when you're demand for power (full throttle acceleration) dictates.

    You have a noble idea, but Mitsubishi beat you to it. The alternator is already as small as it can be, and operates as efficiently as it can to operate the electrical systems in the car and keep the battery charged.

    As with anything of this sort, you're best to start with LOTS of research, and some instrumented testing. You should be able to tap into the alternator control circuit (the wire that profides the "field current" voltage to the alternator to turn it on) and wire that to a light on your dash, or even to a logging system. With that, you'd be able to see exactly when and for how long the alternator is actually loading the engine.

    If you put a toggle switch in that same circuit, you could turn the alternator off at-will.

    I'm going to bet that MetroMPG knows a bit about this from years of playing with this kind of stuff and keeping up with the Ecomodder forum. It totally makes sense on an older "dumb" car, like a Metro. But, I'd be VERY surprised if there was anything to gain by playing with it on the Mirage because it's already ECU-controlled and optimized for fuel economy.
    Simplify and add lightness.

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    I am just happy the Mirage starts every time I hop in it, & it runs great! I guess it doesn't take much to keep me happy. It's still fun to listen to you all think out loud about these things just the same!

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    Senior Member stevedmc's Avatar
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    Disconnecting an alternator? What will they think of next? HHO generators? Flintstone engines?

    I saw a movie once where they took radiators off cars to save weight.

    The fun never ends.

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    I’m interested in your findings Doax. Please report back what you find and come up with.

  6. #6
    Administrator Daox's Avatar
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    Quote Originally Posted by Loren View Post
    The stock alternator is already controlled by the ECU. It switches it "on" when it is needed, and "off" when it is not needed, or when you're demand for power (full throttle acceleration) dictates.
    That is somewhat correct. Per your suggestion, I tested this out today on the way home from work. I'll share that info below.

    You have a noble idea, but Mitsubishi beat you to it. The alternator is already as small as it can be, and operates as efficiently as it can to operate the electrical systems in the car and keep the battery charged.
    Correct! It is designed to charge the battery and keep up with the electrical loads that the car demands. However, I added a deep cycle battery that will take care of the electrical loads for non-long trips, so I don't really need it most of the time.

    As with anything of this sort, you're best to start with LOTS of research, and some instrumented testing. You should be able to tap into the alternator control circuit (the wire that profides the "field current" voltage to the alternator to turn it on) and wire that to a light on your dash, or even to a logging system. With that, you'd be able to see exactly when and for how long the alternator is actually loading the engine.

    If you put a toggle switch in that same circuit, you could turn the alternator off at-will.

    I'm going to bet that MetroMPG knows a bit about this from years of playing with this kind of stuff and keeping up with the Ecomodder forum. It totally makes sense on an older "dumb" car, like a Metro. But, I'd be VERY surprised if there was anything to gain by playing with it on the Mirage because it's already ECU-controlled and optimized for fuel economy.
    I'm going to keep the research stage here short. Its already been done by others thankfully. This will actually be the 3rd car I've done this mod to as well as many overs on EcoModder. MetroMPG's testing is on his website here. He goes as far as removing the accessory belt and it nets him a 10% increase in fuel economy. According to the EcoModder wiki page on this mod, it will net a 5-10% gain in fuel economy. That is pretty huge as far as a single mod goes.


    Alright, enough talk. Lets hear about the testing.

    I have about a 25 minute commute home. I monitored battery voltage the entire ride home, and I took some pictures at the end of the trip to eliminate any 'start up recharging' situation. Voltage will tell us roughly how much the alternator is putting out. Higher voltages are required to charge a battery faster. Typical alternators keep battery voltages anywhere from 13.5 to 14.5 volts.

    When I fired up the car at work, the battery voltage jumped up to 14.5V. This is the start up recharge phase. It slowly went down as I drove for a while, and ultimately settled right around 13.9V for most of the trip. However, I wanted to test it under different conditions to see how the ECU controls things. So, I snapped a few pictures.

    In our first picture here, I am cruising through town (slightly downhill) at 35 mph. 13.8V

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    In this picture, I am in gear slowing down for a red light. 13.9V

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    Here I am sitting at said red light idling. 14.0V

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    Now, I am accelerating away from the light at WOT. 13.8V.

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    So, yeah it seems like the Mirage really likes 13.9V +/- .1V. I was hoping to see the voltage drop a bit more under acceleration as that would free up a bit of power as Loren suggested. However, I really didn't see that happen. I didn't just quickly goose it, I was WOT all the way to the speed limit which as we know takes the Mirage a bit longer than most cars.

    In either case, this mod will completely eliminate ANY electrical load the car will be using. Doing a little bit of math will give us a very rough idea of what this will do for us.

    1 horsepower = 745 watts

    Lets assume that the Mirage uses 20A in normal use. 20A * 13.9V = 278W

    That is nearly 1/3 hp just to run the electric stuff in the car like the spark plugs, the plethora of sensors, abs, traction control, etc.

    But wait, it gets better. If you look up the efficiency of an alternator, they peak at about 60%, more likely we're looking at 50%. This means, the engine is actually being loaded down by 556W or 3/4 horsepower. That may not sound like a ton, but it is significant. According to the Ecomodder power & MPG calculator the Mirage needs 9.7 horsepower to maintain speed on level ground at 55 mph. Add another .75 hp to that, and you add almost 8% to your power requirement. Interestingly enough, that falls into our 5-10% fuel economy gain from eliminating the alternator.
    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar, Upper grill block

    Current project: Alternator delete with regen braking modification

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 45.7 mpg (US) ... 19.4 km/L ... 5.1 L/100 km ... 54.9 mpg (Imp)


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  8. #7
    Still Plays With Cars Loren's Avatar
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    I like it. You're doing (and have done) your homework. There's potentially more to gain than I expected.

    Where that deep cycle battery would really be handy is if you want to get into a lot of ECO coasting... at night.

    I was thinking about this as I was driving today. You're "enable charging when the brake lights are on" idea. If you're properly hypermiling, you're foot is NOT going to be on the brake that much. You'd want to enable charging while you're decelerating, by either somehow triggering on the DFCO flag (I'm not sure how you'd do that), or by using some kind of inertial switch that only comes on when the car is decelerating (or going uphill, which would probably be okay, too).

    My only experience with something like this was the economy run that I did in a Miata with a kill switch and an extra (parallel wired) battery in the trunk. At night, of course. So, I'd kill the engine, and coast down for a very long time (60-65 to 30ish, however long that takes) with the lights and fan still running. The alternator was charging on my "pulse" cycle only. But, it worked fine. Never a problem.

    I was monitoring battery voltage, of course. If it got below 11.9, I just cruised for a little bit to charge it up.

    Will be interesting to see what the real-world results are on the Mirage. They've done SO MUCH in the name of efficiency on this car, it just doesn't seem like they'd have left a whole lot on the table here.
    Simplify and add lightness.

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    Administrator Daox's Avatar
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    I am quite surprised to see they didn't do a bit more with it too. Many other OEMs have 'smart alternators'. They usually relax during cruising and acceleration and use braking situations to charge up a bit more. Its not super difficult or expensive to do either. My guess though was it was a cost thing and they decided not to include it.
    Custom Mirage products: Cruise control kit, Glove box light, MAF sensor housing, Rear sway bar, Upper grill block

    Current project: Alternator delete with regen braking modification

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 45.7 mpg (US) ... 19.4 km/L ... 5.1 L/100 km ... 54.9 mpg (Imp)


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    Senior Member Fummins's Avatar
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    I've seen people drive surprisingly long distances without a working alternator. I had a truck here that ran most of the day before dying on the side of the road. The driver didn't know that the red battery light that was lit all day long meant that they should have told a grown up.
    At my last job a customer came in to buy an alternator for the car he drove there. He needed a boost when he tried to leave, I put a charger on his car and told him he should wait a while. The guy was an idiot and didn't listen. The second his car had enough power to start he left. I passed home broke down on the side of the freeway about an hour later.

    Wonder how much draw the power steering uses? Would running an electric water pump be worth looking into? Could turn it off to help with quicker warm up times as long as you don't get hot spots and warp the head or something. Would be a lot more hassle and fab work than disabling the alternator.

  11. #10
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    Quote Originally Posted by Fummins View Post
    Would running an electric water pump be worth looking into? Could turn it off to help with quicker warm up times as long as you don't get hot spots and warp the head or something. Would be a lot more hassle and fab work than disabling the alternator.
    Now that's an interesting idea, except for the turning it off part as I think circulation is important.


        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 50.0 mpg (US) ... 21.3 km/L ... 4.7 L/100 km ... 60.1 mpg (Imp)


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