How To: Alternator delete

[Daox]

I have recently found out that the battery in my Metro doesn't have a ton of life left in it. Being an ecomodder, I instantly think this is a great time to do an alternator delete mod. So, I figured I'd go through the steps of figuring out how to actually do an alternator delete for anyone who doesn't know already.



Step one is to figure out how much power your car uses so you can size your battery correctly. This is probably the trickiest part to do. The best way to do this is to measure your electrical power consumption with an ammeter. However, for those who don't have an ammeter, Darin posted a great thread on electrical loads a while back which I'm quoting below. Its a pretty comprehensive list, and your car likely doesn't have all these goodies. The Metro sure doesn't. However, you do want to calculate a worst case scenario to size your battery so you know you have enough power no matter what. If you compromise on battery capacity, you'll have to keep that in mind as you drive daily.

Engine Management            Power (W)
Fuel Pumps Injectors         135
Ignition System              60
Electronic Throttle Sys.     60
Sensors a Actuators          110
Solenoids & Relays           20
Subtotal Engine              385
Amps @ 14.2V                 27.11

 Chassis Electrification      Power (W)
Electric assist steering     300
ABS brake system             200
Air suspension valves        50
Air compressor               500
Subtotal Chassis             1050
Amps @ 14.2V                 73.94

 Charging System              Power (W)
Alternator                   3000
Battery (80 Ah)              1000
Starter motor                2200

 Multimedia & HVAC            Power (W)
High end audio sys.          300
Navigation and GPS           150
Driver information display   30
Cabin climate valves         75
Blower motor + ECU           370
Subtotal Cabin Sys.          925
Amps @ 14.2V                 65.14

 Lighting (Exterior & Interior) Power (W)
Headlamps (2)                120
Running/Park lights (4)      130
Turn signal lamps            130
Center high mount stop        65
Back-up, interior, license    45
Subtotal lighting            490
Amps @ 14.2V                 34.51

 Body Electrical              Power(W)
Power Windows (4)            560
Power Door Locks (4)         200
Wipers and washers           140
Heated backlight             500
Power seats (2)              460
Subtotal Body Sys.           1860
Amps @ 14.2V                 130.99

 Future Systems              Power(W)
DVD and in-seat displays    
MicroJMild-hybrid functions    
Active suspension    
Frontyrear radar    
Obstacle detection & Airbags    
Active cruise control    
Total Electrical/Electronics    4710

For my specific case, I know the exact electrical loads thanks to Darin and others on this forum. Here is an exact list of electrical loads for the Metro.

So, for my example lets add them up to get a worst case. My worst case scenario is a winter commute of ~15 miles per day. This equates to roughly 30 minutes of driving. Obviously the engine must be running for some of this, and the engine pulls roughly 140W or 10A. Since its winter, I want heat, so my fan will be on some of the time. I'll use fan setting 3/4 for 140W or 10A. Its also dark out, so my lights will be on which uses 240W or 20A. The total for these loads is 40A.

This means I'm using 40A for 30 minutes. Battery capacity is rated in amp hours (Ah). So, if I use 40 amps for a half hour, I've used 20 Ah. This would be just enough power to get me to work and back under a typical bad weather scenario. However, I do take the occasional trip that is longer than 15 minutes, and what if I want to run some errands after work? Well, we need more capacity.

In my case, I don't use the Metro for long hauls. But, I go to occasional lunch meeting and what not. So, I would like to aim for 1-1.5 hours of run time. Using the above calculation, for 1.5 hours of run time at 40A, I need 60Ah of battery capacity.

So, I need 60Ah of usable battery capacity. If I go with lead acid (which I probably will), the rule of thumb for optimum battery life is to not exceed 50% depth of discharge (DOD). This means don't discharge the battery beyond half of its capacity. Now, for 60Ah of usable capacity, I need a 120Ah battery. This is what I should be aiming for. Quite a far cry from the 20Ah I initially calculated.

If you wanted to get fancy and go with lithium, their rule of thumb for DOD is 70-80%. This means you'll only need a 80-90Ah battery.

Sizing the battery in this manner will ensure that you have enough power to get around without the alternator without worrying about it, and it will also ensure that your battery will live a long happy life without you abusing it.

So, that is step one.

A 120Ah battery is fairly large, so we'll see what I can actually fit into the engine bay of the Metro. I may compromise and drop down to a smaller battery and just use the alternator for those longer trips, then turn it off on the way home.

[Cobb]

Since you are going through all this trouble, why not mount the battery else where for better weight distribution or inside for better regulation of operating temperatures?

[Daox]

Its a Metro, not a race car. The weight distribution is fine for daily driving. Having it inside the cabin would be nice, but not worth the hassle of running wire, mounting, etc.

[Cobb]

Im pretty sure a 120 amp, group 27 deep cycle battery in the trunk would really balance out the 3 cylinder under the hood. 2 group 24s, etc arent light either.

[mechman600]

Obviously a 120aH lead acid battery is the cheapest way to go, but ideally, a DC-DC converter should be used to maintain constant accessory voltage as the pack starts sagging.
I would do a 48V pack & charger (lithium, of course ) with a DC-DC convertor down to 13.5V.

Is it possible for you to chuck the alternator belt, or does it drive other accessories? The nice thing about my Civic is that it has three belts, one for each accessory that I could potentially delete.

[redpoint5]

I'd go LiFePO4 to get deeper depth of discharge and longer life, along with weight savings.

The voltage should remain higher during discharge than a lead-acid battery.

[Cobb]

I run a similar setup with a dc to dc converter in my honda. I wouldnt delete the starter battery as there are times the converter cuts out or rolls back output.

Then you got the ROI. In my case I had all the parts, it was just a matter of wiring it all up.

[Daox]

Thanks for the suggestions guys. I may have to go with something like that. I tried a couple batteries in the Metro this morning and it is looking like I have a height clearance problem.


Here is the stock battery.




Here is the stock battery next to a group 31 battery, what I'd ideally like to put into the Metro. Slight size difference. The thing you can't see in the picture is that the group 31 is over an inch taller.




Here is the group 31 battery in the Metro. Looks almost comical IMO.




However, this is what happens when you try to close the hood. So, the group 31 battery definitely will not fit under the hood. Bummer.




Now, here is a group 24 battery I had kicking around. I managed to get it under the hood and the hood even closed. However, its really only on the tray a little of half way, so I'd have to modify the battery tray to hold it properly.




So, I'm looking at a few different options at this point:

First off is seeing what kind of capacity I can get in a group 24 lead acid battery. If its 80-90 I might just settle for it as it'll be the easiest thing. Modify the battery mount and be done.

The next option I have is going with a smaller battery up front, and sticking a group 24, 27 or 31 in the back somewhere and using a DC-DC converter or something as Mechman stated. I like this option as it runs a more normal voltage while driving. But, honestly I didn't have any issues running without that on my Paseo when I had an alternator delete. I'd also need to find a DC-DC converter capable of pumping out around 40A which isn't a tiny amount of power.

The third option would be go size a ~100Ah lithium pack as redpoint5 stated. This would be the most expensive option, but it should theoretically last quite a while. I'd need lithium cells and a lithium charger at the least, possibly a BMS.

[2000mc]

this isnt a cheap idea, and the work mounting may not be alot easier than making a trunk mount, but would a group 31 AGM battery fit on its side?

[Cobb]

Ive used an electric wheelchair for 9 years and with deep cycle lead acid batteries they take 10-12 cycles before they build up capacity with use. Ironically they start to charge faster and hold the charge longer once they break in.

Those are nice wheels on the prius to the right. Is it yours?