Alternator delete with regen braking modification for better MPG

[Daox]

I agree. Sadly, the only dc-dc converter I've been able to find with that large of an input voltage is $20. Not too bad, but a few dollars in components would fix things too.

[Mitz]

Daox may I suggest that you take look at these

LM2596HVS DC-DC Buck Converter Module

• Input voltage : DC 4.5 - 60V
• Output Voltage : DC 3- 40V
• Output Current : 3A(MAX)
• Conversion efficiency : 92% (MAX)
• Switching frequency : 150KHZ
• Output ripple : 30mV (MAX)
• Working Temperature : industrial (- 40 ° c to +85 °c)
• Size : 43*21*14 mm

MT3608 2A Max DC-DC Step Up Power Module Booster Power Module For Arduino

• Input voltage range : 2-24V DC
• Output voltage range : Max 28V DC
• Efficiency : 93%
• Output current : 2A
• Size: 3.7 * 1.7 * 1.4cm/1.46"*0.67"*0.55" (L*W*H)

They are both small in size and are cheap.

[Daox]

Those look like they would work! Nice find Mitz.

[Daox]

A bit earlier this weekend I finished up the wiring for the charger. The 110V lines got blade connectors while the 12V lines got bullet connectors. I then stuffed the charger behind the center console.

I have a new 5 to 15V dc-dc converter on order for phase 2 of the project.

[Loren]

I know you won't be driving while connected to AC power, but we don't want you to burn your house down, either. What kind of wire are you using to connect that AC? Looks awfully light gauge, and thin insulation. I know it's not drawing a lot of amps, but if the wire is too small, it will get hot... bad things happen when tightly routed wires get hot. And if it's not got heavy-duty insulation and chafes against something... that could get ugly, too.

You're not wiring speakers or light-duty 12vdc on a 10A fuse here. This is connected to home AC, and unless you give it a dead short to ground, it won't trip the circuit breaker, it will just keep pumping power to it!

I'd have gotten a cheap outdoor extension cord and cut that up. Much more rigid, and rated for what you're doing.

[Daox]

It must just be the picture. It is the cord that came with the charger. I think the 110V wiring is 16 or 18 gauge. The charger pulls 90W while charging, so that is under 1A at 110V. The 12V wiring is a little thicker.

[Daox]

Whilst waiting for the new dc-dc converter to arrive. I should probably think up how I am going to do the regenerative braking thing.

Ideally, we really only want the alternator turned on during a certain set of conditions:

1) The alternator is spinning.
and
2) We are slowing down.

I haven't really found out a great way to do this yet. Initially I was thinking that I would just take a signal from the brake lights. When the brake light would go on, the alternator would turn on. Unfortunately, this really doesn't actually ensure either of the two conditions are met. It simply means the brake is on. I could be sitting at a stop light, or starting the car on a hill. In both of those cases I don't really want the alternator to turn on. However, it does make enabling the alternator a simple affair. You get brake light signal, you turn on. Pretty easy. The complicated route would include watching the speed sensor to ensure you're actually slowing down, and probably watching the tach signal to make sure the engine is running. I really don't feel like doing all of that though haha.

So, for now, I think I am just going to hook it up to the brake light and see how that works. I can always tweak it in the future. But, if it works, there is no reason to make it more complicated.

As always, if you have suggestions I'm all ears!

[Loren]

You could experiment with a Mercury switch. (Do they even make those with Mercury any more?)

Set it so that it only comes on when you are decelerating. It would also come on when you're going downhill, but that's probably okay, too. Depends on where you drive.

[Daox]

Looking ahead to phase two of this modification, we're looking at using the alternator as a regenerative brake. Before diving in, we should probably consider what benefit this can actually bring us as we're adding more complexity to the system. Its always good to ask why and if its worth it. So, lets do some math!

Lets start with the alternator. It is rated at 85 amps. For our calculations, we're going to assume that during braking it is putting out its full rating. In actuality, it will be less than that. Also, we're going to assume its putting out 15V since I mistakenly figured out how to make it do this on command.

So, lets take 85A x 15V = 1275 watts. This is how much power the alternator is putting out during braking.

Now, we have to figure out how long we're braking for, and we can get a volume of energy potentially captured during the regen braking. For this example, lets say on average we brake for 10 seconds for each stop. This gives us 1275W * 10S = 12750 watt seconds. A more common unit of measure is watt hours, so lets convert to that. 12750 / 3600 seconds per hour = 3.54 watt hours. This is how much energy we capture on average for each stop we make. Doesn't sound like much does it? Its not lol. For example, the Iphone X's battery holds about 10 Wh. So, 3 stops would fill your iphone from totally dead to totally full. Not much power considering we're stopping a ~2000 lb vehicle, but it would be cool if you could charge your phone in 30 seconds eh?

Of course, we don't just stop once on most trips, we stop multiple times. On my trip to work I stop about 10 times. So, I'll regen about 35.4Wh on the trip to work. That number still sounds a bit nebulous to me. Lets convert that 35.4 to amp hours which we can use to compare to the battery in the car. 35.4Wh / 12.5V = 2.8 amp hours. The battery I have is probably around 80 amp hours. 2.8 is about 3.5% of 80, so on the trip to work, and back home, I can regenerate about 7% of the total capacity of the battery. Thats not too shabby if you're looking to extend range.

Thats all a lot of mumbo jumbo Daox, just tell me if it is it worth it?!?!? Thats really up to you and your personal preference. I will probably end up doing it just for the exercise of trying it. I learn more on every project like this I do, and I really enjoy that. Its also pretty neat, and has some 'cool' factor IMO.

[FloridaG4]

During your work week will you be using more battery supply vs regeneration by braking where you would have to recharge the battery every few days or a on a weekly basis?