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Daox 10-22-2019 03:23 PM

A better alternator delete
I think alternator deletes are a really great mod. They give you a sizable gain for just one modification. I've had them on just about all my daily drivers for the last decade. However, they just are not usually cheap. First off you need a deep cycle battery. If your starting battery is fine, its hard to swallow $80 for a new battery. If its dead, its not too big of a deal. Then, you need a charger for this battery. Let’s say this charger costs you $50 (I'm pretty sure mine cost more). Now you're up to $130 for a single modification. Next, you need to actually do the mod which can range from inserting a switch in some wiring to coming up with a small electrical circuit like I've had to do on my Mirage. Lets say this costs another $10 for a total of $140 for an alternator delete. Yay, you get a nice bump in MPG, but that $140 can get you a lot of gas too, right? What if there were another way?

You've probably already seen my post on battery hookup. If you haven't, I highly suggest it because it seems like a great place to get some lightly used lithium batteries. They're keeping these things out of landfills and getting us DIYers a great source for lithium batteries. With the prices they have I've been thinking more and more about what I can do to improve mpg via battery use without spending a small fortune.

My idea for today is a portable lithium battery pack that essentially doubles as an alternator delete. What I'm talking about is a smallish lithium ion battery pack that is 15V+. This pack has a voltage regulator on it that sends the 15V+ to your car's 12V battery via a PWM signal. The power out of the portable pack will keep the car's system voltage just above the voltage set by the alternator, thus disabling it. This is the same idea I used on my Mirage to disable the alternator and it works great. When the lithium pack is depleted, your car goes back to using the lead acid starting battery as normal.

I'm pretty sure we've talked about this before... kind of. A lot of you apartment dwellers don't have access to outdoor charging. This portable pack solves that problem. Take it in at night and you can charge it in the warmth of your building. This also solves the problem of some lithium cells not being able to be charged at freezing temperatures. When you go out to the car in the morning, simply plug the pack into your cigarette lighter (or other plug of your choice) and you're ready to go.

Another benefit of this is that your car's system voltage is actually where it is supposed to be, not at 12.X volts. This means no more dim headlights at night, or slow wipers. Also, no hacking car wiring. This thing literally can plug right in, and come right out.

On top of all that I also think this is doable for less than the 'old' way of doing an alternator delete. Here is my guestimates for cost:

lithium pack - $30 (from battery hookup)
5S bms - $13 (price from amazon)
5S charger $17 (price from amazon)
voltage regulator - $15 (DIY circuit? rough guess)

Total: $75

So, roughly half the price. If you use a cigarette lighter plug you can literally use this thing on any car you jump into.

MetroMPG 10-22-2019 06:27 PM

I like this idea!

I'd be surprised if nobody in the history of EcoModder has ever done this before (I once thought about doing it with a DC-DC converter powered by 24v).

But the difference today is the availability of cheap used cells and cheap electronics to make it work - almost plug 'n' play.

Planning to try it out?

redpoint5 10-22-2019 06:40 PM

Well, it was discussed in the Virtual Alternator Delete thread.

I planned to give it a try, then I had a kid, bought a house, still renting another house... also I hardly ever drive anything other than the company car now that they provide unlimited fuel for it.

In 2 years when I have to turn it in I'll re-evaluate the feasibility of the Runzheimer program where I would get compensated some amount for using a personal vehicle for business.

Daox 10-22-2019 08:21 PM


Originally Posted by redpoint5 (Post 610060)
Well, it was discussed in the Virtual Alternator Delete thread.

Aha, I'll have to find that one. I must have missed it. :thumbup:

redpoint5 10-22-2019 08:35 PM

Ah, "virtual" was misspelled in the title. Here it is.

oil pan 4 10-22-2019 09:39 PM

I think "the better alternator delete" the alt stays in the car unbelted and electrically isolated and can be quickly returned to service if needed.

mpg_numbers_guy 10-22-2019 09:42 PM

This does seem like a great idea, but for couple possible concerns:

- Charging a lead acid battery is less efficient than lithium. IIRC only about 80% of the charge to a lead acid is actual charge, and that number lessens when reaching the float stage. And if you're not floating a lead acid, it's life is going to be shortened.

- Do you know that the 5S Amazon BMS is a good one? There are a lot of cheap BMS out there that fail on short notice. And then since you're relying on the BMS to manage the battery, if it goes kerplunk, you likely won't know of any battery issues until it's too late. Obviously LiFePO4 is much more robust but it won't be good for the life of the battery. From what I've seen, a good 4S-5S BMS is anywhere from $40-$70. Then again if it were to fail, it would be much cheaper to replace the battery than to spend $ on a higher quality BMS.

My thoughts are:

Why not just replace the lead acid with the lithium, and use a switch for the alternator like you've been doing? There would be fewer charging inefficiencies due to going from battery to battery, and you'd also save some weight by eliminating the lead acid battery altogether.

....but that's just me being an extremist ecomodder, where if I do an ecomod I have to go all the way for efficiency and leave nothing on the table (80 PSI tires.. :rolleyes:). Other than that it seems like a great idea. Maybe replace the normal 12V starter battery with a small 12V lithium battery in addition to this? but then most small lithium batteries don't have the cranking amps available.

This would definitely be a much simpler way of doing it, although I surmise that the efficiency gained would be slightly less than doing a direct lithium replacement and alternator cutoff. But since we're talking about, what, a 5%-10% gain from deleting the alternator, the difference between these methods is likely <1%.

Here is a 32.95V 2.9ah pack with a built in BMS for $25. Considering 90% usable capacity @ 14.4V gives around 6ah of capacity. Two of them brings you to $50 for 12ah@14.4V and you don't have to worry about rigging up your own BMS. A cheap DC-DC converter to trickle charge your 12V battery from the larger pack.

I'm not too sure about a PWM voltage regulator. I really don't know anything about them other than that I've read that PWM solar charge controller's lower the voltage but don't up the amps (i.e. a 18V/2.75A/50W solar panel through a PWM charger puts out 2.75A@14V (38.5W), which wastes over 20% of the energy as heat. Now I have no basis for assuming that other PWM voltage regulators work like that, but that's just what I've read. A small, 100W DC-DC converter isn't that expensive and usually much more robust.

redpoint5 10-22-2019 09:58 PM

My idea which I posted in the other thread is to have 2 battery harnesses in parallel in the cabin. I take a freshly charged lithium battery and plug it into the harness, and remove the previously used one to charge it indoors. Each time I take a trip, I'm starting out with a freshly charged battery, and not subjecting it to cold temperatures while it gets recharged. When the battery drains to a certain voltage, the alternator kicks on and maintains voltage.

No brain power required with this, as the only thing to remember is the freshly charged battery each time.

I bought a 5aH battery to experiment with... this thread might push me over to the point of testing. Maybe I'll work on the wiring tonight and connect a harness to the Acura.

Daox 10-23-2019 02:55 PM

The other thread:

Virtual alternator delete.

Daox 10-31-2019 04:07 PM

2 Attachment(s)
I decided to give this thing a shot. I like Redpoint's idea of using a lithium battery in parallel, but I would like to give this idea a go. I have somewhat changed the design a bit though.

First off, the voltage regulator will be a 300W dc-dc buck converter that I found on Amazon for $14. This will take the 17-21V from the lithium pack and convert it down to right around 14.5V for charging the lead acid battery. The voltage will be set to right above what the alternator charges the battery to.

I am also going to ditch the BMS in favor of individual cell chargers. I was able to purchase 5 12V 3A power supplies for $3 from These power supplies will put out 12V to a 5A dc-dc buck converter that is set to whatever cell voltage I want, probably 4.0-4.1V. This will balance each cell every time it is plugged in to charge. As long as it isn't discharged too far, it shouldn't be a problem.

The last piece major of the puzzle is the batteries. I still haven't figured this out yet. Battery Hookup is out of the cells I really wanted to use, and they are also out of stock on the second choice as well. These were mainly my choices as their prices were very low. As I piece things together I'll keep an eye on what they have. If all else fails, I'll just build a pack from 18650 cells.

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