# Interested in Understanding Limitations to 12V DC battery applications

1. Feb 14, 2008

### Mattsnooze

In a 12V dc typical car how could you possibly obtain a 24 volt power source that would charge off the existing alternator, without upgrading the entire car to run off the 24V power source?

In the engine bay I would like to have access to 24Vdc power so was hoping I could either install two 12Vdc (oddessy marine batteries) and somehow be able to tap off of
24Vs some how without heavily modifiying the car (keep the budget as low as possible).

Thanks in advance to any repliers

matt

2. Feb 14, 2008

### mgb_phys

You could add 2 x 12 batteries as a separate system - or just use a 24V auto battery. Trucks and military vehicles use 24V systems so they have extra power to run extra equipement. You would have to fit an extra 24V alternator and charging system.

You can easily convert 12V dc to 24V dc if you only want to run some electronics, it wouldn't be very efficent for high power applications.

3. Feb 14, 2008

### Danger

Welcome to PF, Matt.
This is not one of my areas of knowledge, but I can tell you that a typical alternator puts out over 200VAC. Power converters can either take that from the source and modify it, or take the 12VDC from an auxilliary power tap such as a lighter socket and run it through an inverter.
If you want to run a 24V system, you probably just need to replace your voltage regulator (and every 12V component in your car).
It might be easiest to just go to your local airport and talk to a few sky drivers. Civilian aircraft (at least when I was flying) are 24V systems.

edit: Hey, Mgb... how do you always manage to beat me to the punch? (No age jokes allowed.)

Last edited: Feb 14, 2008
4. Feb 14, 2008

### mgb_phys

Having a bad day at work, so it's hit 'new posts' on pf or work out which of the dozen mutually incompatible but high priority changes I'm supposed to work on first!

5. Feb 14, 2008

### Danger

Man, I'm glad that I work in finance rather than engineering. :rofl:

6. Feb 14, 2008

### rcgldr

You could use a setup that kept the batteries in parallel, then disconnect them and rewire them up in series when you need the 24V.

7. Feb 14, 2008

### Danger

Actually, that would be a really simple switching circuit. Alternatively, he could set the charging system for 24V, and use a secondary regulator to feed the rest of the vehicle.

8. Feb 15, 2008

### Mattsnooze

Well, I'll explain what i'm doing and see if your all able to expand upon my thoughts

Heres the scenerio without all the science. I have a DSM turbo (14B) off a mitsubishi. The bad part about regular turbo systems is the heat they generate using the exhaust to power the turbo. I would like to use a DC motor (12vdc requires higher ampherage, and less 12V DC motors are available for the application I would like to use it for). 24V dc have a wide veriety of DC motors that would fit my application so was hoping I could maintain my 12VDC car but just add in a power supply that charges off the alternator, but could provide me with 24VDC at a push of a button to turn on the DC motor which will either use a pulley system or direct drive depending on how much space I need and at what speed/rpm/torque will put me at my 1.4 PR. My alternator puts out around 100 amps so the motor ideally would use less than 40 amps at max. Also the good thing about using a dc motor to power the compressor is that speed regulation would be very simple (boost control). I origionally thought about using a power inverter and buying a 120V ac motor but I was concerned about space and about limitaions of power inverters (ampherage, and cost of the inverter itself) I have built a prototype that works fantastically but like I said I need this 24 volt system in my car to make it work as I have built it. Then ofcourse comes the tuning lol (the fun part). IF however someone knows where I can find a 1/3 to 1/2 HP 12VDC motor that has around 5-8000 rpm with a good deal of torque (enough to power a small impeller off a turbo at high speeds (50000-100000 rpm) (thus needing a pulley system) for under 100$I could purchase that instead of trying to convert to 24 VDC. Could I not just add a 12VDC to 24VDC transformer to strictly power the DC motor? That would double the ampherage draw on my battery and alternator system though would it not? That transformer would have to handle the 40 amps though my motor draws, so In the end a 12Vdc motor would be the Easiest/Simplist. (suggestions ?) The whole bases of this project is to boost a car at around 6psi (approx. 80000 rpm at my 1.4 PR) as inexpensive as possible without having as much heat generated by the design of the turbo system (using exhaust to power the compressor side of turbo) Thanks for the welcome btw, and all your responses!! 9. Feb 15, 2008 ### stewartcs The timing would seem to be the biggest issue. Not sure how you could tune it. Why do you have such a concern with the heat in a normal turbo?? CS 10. Feb 15, 2008 ### Danger Have you considered just using a belt-driven supercharger such as a Paxton? Those mount similarly to an alternator, on the side, so you don't have to cut a hole in your hood. For a high hp/torque 12VDC motor, check out a local wheelchair supply company. I have 3 surplus wheelchair motors that are 1/2hp 12VDC; they're awesome. 11. Feb 15, 2008 ### NoTime Along with what Danger said you may want to look into intercoolers. All compressed air gets hot and engines work better if you cool it off before dumping it into the cylinder. 12. Feb 15, 2008 ### Mattsnooze Intercooler is already part of the plan. I have all that I just need the power supply I have the system built already, EFInd (electrically forced induction) like I said, its built on a flat board that simulates the size in my engine bay to fit the whole setup with the two odessy batteries even. I have the intercooler designed (just need money to buy a half intercooler but piping will have to be custom). All I need is a way to either get a good 12V dc motor (1/2 hp wheel chair motor I have researched and are perfect but a little bulky for what I want and are really pricey. I can't find any slightly used for sale). Or plan B some how as I stated above use a readily available decent powered 24V dc motor but have the complications of supplying the 24v dc power to it without it costing too much to convert the car to 24v dc. The superchargers you list are fine but draw parsistic lag on the motor, while all I'm doing is using an abundant supply of free energy (wicked alternator powering 1 hopefully 2 odessy marine batteries if I can figure a way to run the 24V dc) to power a tdo5h 14b dsm (compressor side) using a pulley/belt system. The bonus is the whole setup (EFInd) for a small 6-8psi boost is under$2000 with tuning incorperated, where as a small turbo setup of same power output would run probably 4000-5000 if done properly.

I'm using a speed control system also for boost control which is why electrically forced induction is made really simple. Its pretty much a variable speed control, (controlling the motor) with a boost guage, and botv still to max out psi at hopefully 8psi max (if they even make a botv at 8psi)

As far as tuning goes I would need a p72 tuned with new maps that opperate with 8psi potential. My stock map sensor will be adiquite so with a proper tune program it will regester in the p72 and it will alter my timing/fuel accordingly. Thats the last thing I buy though, thats going to be 500+ than with dyno and tuning another 200 or so.

Last edited: Feb 15, 2008
13. Feb 15, 2008

### NoTime

Errrrrr, so you don't think the alternator is going to place a parasitic drag on the engine?
Sorry, not a chance. It will also be much less efficient than direct drive.
There is no such thing as free energy.

14. Feb 15, 2008

### chroot

Staff Emeritus
This sounds like a pretty dumb idea. Your new alternator + battery + motor system will likely be less efficient than the exhaust-driven turbo you're trying to replace, meaning it will put an even greater load on your engine. Yes, alternators get harder to turn when you apply more electrical load. No, it's not "free energy" at all.

Heat is not really an issue, as compressing the intake air is what raises its temperature, regardless of how you choose to compress it. I doubt that a substantial amount of heat is transferred from the exhaust to the intake side of the turbo in the first place.

The only real advantage I could see would be the ability to dial up whatever boost you want, even at idle, but I hardly see this as a reason to build this at all.

- Warren

Last edited: Feb 15, 2008
15. Feb 15, 2008

### Danger

I agree with Chroot, but was trying to be polite. An electrical drive would be far less efficient than either a belt drive or a turbo. In the old days, we would disconnect the alternator wires before a race to cut down on the EM drag. A belt driven supercharger such as a 6-71 Roots, if driven independently from the engine, might give you something like 200 extra hp. If the engine is powering it, though, you might see only a 50 hp increase because it takes 150 to run the damned thing. Even a turbo robs power, since it increases the exhaust back-pressure. Since nobody needs any kind of performance boost under normal circumstances, maybe you should just consider tossing in a nitrous kit.

16. Feb 15, 2008

### NoTime

The approx 150lbs of batteries and drive motor ain't going to help matters either.

17. Feb 16, 2008

### Mattsnooze

Heh, thanks for the non constructive critism. Like I've said...

It works, theres no question, my alternator puts out 200 amps as opposed to the typical stock 90amps. So I have an extra 100 amps+ of potential unused FREE energy . I know parasitic lag from the alternator exists but we are only drawing less than 40amps (to turn the motor)(P= I x V therefor 375 = 12 x X therefor X = 31 amps) so my car runs off 70 MAX when idling so in reality I would have 130 amps that could safely be consumed (in spurts (non-continous)),.

We are talking like a nos system that is turned on when needed using a variable speed control system that could even be tied in to tps (most likely controlled through tuning software via tps sensor anyway lol) (BTW alternator was already replace because my stock one is 800 dollers (new at honda)) so needless to say the high end performance one (200amp) was the logical choice for around 400$. Looks way better too all chromed up. As far as weights concerned total weight in parts including the two odessy marine batteries, compressor housing/wheel, inlet filter, botv, air bypass valve, and my current motor(prototype chosen 24V dc motor 1/2 hp) is 51 lbs and thats not even including what I would take out by removing my single 12vdc huge typical battery. This also excludes what intercooling setup I will impliment but it won't be much at all in weight. I've removed my stock intake resonator (20 lbs) and have done lots of weight reduction so added weight is not an issue. Cost IS however and all these systems you guys are recomending are thousands upon thousands of dollers. So again, please keep responses to ways to turn this shaft, either a 24 v system where I can maintain my 12v dc car system, or a 12V dc motor that occupies less space than approximately 10" square but can put out around 5000-8000 rpm with a wattage around 375 (1/2 hp approx.). Danger, and your reasoning of the belt driven supercharger is why I don't go those routes. Those draw HUGE parsitc lag and are costly therefor arn't cost affective. We are talking numbers here. Those systems cost 3000 dollers to give you maybe 100 horse MAX, and the system I have assembled is less than a 1/3rd of that and will put out 60 hp on a 2.3L engine 2200 approx cc engine. The turbo is more efficient (the cheap one I bought isn't, its probably 65% (new ones for 600$ are like 85% efficient) but I got mine for 40$(compressor side of turbo) Chroot. As far as heat transfer between exhaust side and compressor side there is "tonnes" that get transferred but it depends on your turbo system. If its oil cooled, or water cooled, and if it has an intercooler (upon a million other factors like Pressure ratio etc), will factor how much heat is transferred to the actual intake. I guess it depends on how much money you got. If you can sink$5,000 into a turbo system you can incorperate a wicked Water cooled turbo, with a intercooled system and get an efficiency of 85% or maybe higher (I dont know how efficient they can be, being the new technology they come out with on a daily bases). But If you dont have 5000 dollers, then your whole system is going to be actually around 60%-70% efficient range where as my system would be above 80% efficient (in comparison to how much power is produced to how much is used to generate it).

So either way its belt driven (which kinda sucks but direct drive will not get my gear ratio high enough to spin the impeller 50000 rpms unless I could find a gear motor thats gearing increases the rpm output by 10x), so I know I have losses there but thats it.

All your input is valuable either way, just like I said if you could focus on what power supply (how I could adapt a 24V dc supply charging off my alternator, while maintaining my stock 12Vdc car because the full 24V dc conversion is expensive) and If you know where I can get a good half horse 12Vdc motor that can spin at more than 5000 rpm, chime in. Thanks!

Last edited: Feb 16, 2008
18. Feb 16, 2008

### Danger

I'm afraid that I'm going to have to bail on this one. I've expended what little knowledge I had of the subject. Good luck with the project. I'll keep reading to see how it goes.

19. Feb 16, 2008

### Mattsnooze

thanks man!

20. Feb 17, 2008

### Mattsnooze

Would anybody be able to suggest a forum that is specific to dc power/motors?

As above states. I was wondering if anybody here had any suggestions to a forum that would be better suited for dc motor/ dc supply theory/physics?

thanks again for any help anybody may provide!

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