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New to the forum. I have a question about how much voltage I can put into the electric system of my car. I have plans to build a 4s100p Lion battery pack for my car. I have an engine kill switch and do a lot of coasting which kills my lead acid battery quickly. Also when I start up the engine to get back up to speed, my alternater uses a lot of HP from the motor decreasing efficiency. I want to get the voltage to a min of 14.5 so the alternator never turns on. I may end up dissabling it in the future but for now I just want to boost it over the charge cut off so that it will not put any drag on the belt. 4.23v is the max voltage of the cells I have. 3 cells in serial does not provide enough voltage. 4 in serial provides 12v at fully discharged and 16.92v fully charged. I know that it will run just fine on 15.2v, and I may end up just never charging them to full. I am worried that if I run the car from 16-17v that it might damage the ECU or some other modern electrical device. What would be the maximum safe voltage to feed the electrical system at? I want to charge the battery's to the fullest possible capacity, but I think I will need to stop short, perhaps 15.8v. I do not want to just experiment until my car brakes. Thank you.\

My car is a Ford Focus ZX3 3D 2.0L Zetec basic non sport 5 speed manual. Manual windows, no AC, I do not care about the radio blowing up. I just want to not burn up the engine electronics.
 

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Discussion Starter #2
I am using a bank of ultra caps 17v max to turn the starter and reduce current spikes from the battery bank. My other option is using a higher voltage such as 48v and use a DC to DC buck converter to drop the voltage to 15v. Although most DC DC converters are only ~80% efficient so I might as well just not charge the battery's all the way and just leave it at the max safe voltage. Which is why I want to know what that number is. :p(y)

Happy fourth of July. 馃嚭馃嚫
 

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Zetec alts will tend to crack diode plate connections at any higher volt, the plate is poorly designed. They can barely maintain 15 volts without failing. The regulators fail quickly too past about the same amount. Heat control from the PCM is what lets them go even that far, if getting hot the PCM will cut back on volts and if the volts don't drop kiss the regulator goodbye, they are sensitive as spit.
 

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Discussion Starter #4
So if I unplug the alternator, what do you think the rest of electrical system can do volt wise? There are chargers that charge at 16.2, so I think I can get away with that right? If the overvolting does harm to the computer what is likly to burn out a surface mount resister/fuse, or something much more expensive. At 15.68v the battery should last for a lot more recharges. I would rather run them at 16.5-16.8.

If the alternator wires are unplugged the alternator will be okay and not put a bunch of drag on the system nor tare itself apart without a load?

Thank you for the information on the alternator.
 

Grey Friar
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New to the forum.
...
I have an engine kill switch and do a lot of coasting which kills my lead acid battery quickly. Also when I start up the engine to get back up to speed, my alternater uses a lot of HP from the motor decreasing efficiency. I want to get the voltage to a min of 14.5 so the alternator never turns on. I may end up dissabling it in the future but for now I just want to boost it over the charge cut off so that it will not put any drag on the belt. 4.23v is the max voltage of the cells I have. 3 cells in serial does not provide enough voltage. 4 in serial provides 12v at fully discharged and 16.92v fully charged. I know that it will run just fine on 15.2v, and I may end up just never charging them to full.
...
Welcome to FF.

I wish I knew the answer, but I don't know what max voltage the headlights, senors and ECU protection can stand. I'm a mechanical sort... happier fighting a stripped Allen head bolt than any electrical mystery.

That said, I'd like to know a bit more, if you don't mind. Why do you do that? Hyper-miler? What's the most MPG you've reached by driving that way? What other changes have you made?

Just a guess, but it may be better to rewire or reroute part of the harness, so you can make changes safely and avoid power spikes and/or minimize charging. Here's a nice racecar support website that may help you find a workaround... there are some interesting diagrams down the page. Proper Racecar Wiring Principles -PLEASE READ & SHARE! 鈥 Davis Technologies Like, maybe you could minimize charging drag by splitting > lights, starter, cooling fans on the powerpack, and everything related to management on the stock system... coil is a big deal though, and maybe rig something up to allow management to be separate from delivery.
 

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Discussion Starter #6

Grey Friar
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I checked that out, pretty cool. There are several parallels between hypermiling and racing, as far as car prep is concerned. Power-to-weight and rolling resistance are goals for both (I assume you have lightweight wheels with skinny tires). I didn't see reference to drastically lightened your car, to increase power-to-weight. Have you stripped the inside to your minimum passenger requirements? I know you are working on a budget, so you won't be buying racing battery to replace your heavy lead-acid one, but there are several pieces of material in the engine and passenger compartment that are there for sound or cushiness... the weight saving may be inconsequential, if you still want a car that will carry a passenger or three, but you took your mirror off, so, not out of the realm.

Getting rid of your catalytic converter will help somewhat, they are heavy, reduce engine power efficiency, and contribute to acid rain. The environmental damage done would be a wash, or a net-positive, between the increased good they do eliminating smog and the harm they do killing or stunting plants that thrive in neutral or basic soils, and the soil erosion cats contribute to, and the increase in rotting speed of untreated wood, etc. I prefer not having a cat at all, on any car, so we (all of us) can behold the incredible damage we are doing to the environment... the smog would tell us daily, that we are killing ourselves (and many things) with excessive driving and commuting in gas-hogs.

There are other things, but most are not in a college student's budget. One more thing that will reduce air resistance is lowering your car. You can find lowering springs for sale, sold by people who tried them and didn't like them. Or in worst-case, cut a coil off (not recommended for ride quality or cornering performance). Either way, you will have to pay for a wheel alignment... but then, zero toe front and rear will also help significantly, reduce rolling resistance and increase coasting time. I mention these things, because I didn't see them in your post on the other site.
 

Grey Friar
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Almost forgot... you can run 0W-20 without damage, although, not recommended for summer. I used it in my SVT in winter, without problem (Amsoil Extended Interval is best, IMO).
 

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1. Why are you doing hyper-mileing?
2. Why are you trying to hyper-mile with a Focus?
 

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Discussion Starter #10
1. To save money and because it is fun.
2. I got a good deal on it and it has a manual transmission. Ya it is not as good for it as a geo xsi, but the xsi you can get today is beat up something fierce. I could have got a gen1 honda insight but that would have cost me a LOT more. This little focus I have is a great little car that is a able to get over 40mpg highway without ever shutting off the engine. Why not use it in this way?
 

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Was curious to why.
-
Have you thought of using Lithium Iron
Phosphate (LiFePo) batteries?
They match automotive voltages better & have long run times.
 

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Discussion Starter #12
I got these battery's from salvaged laptop packs. I could not afford new cells right now. You are correct though, that would be a good option. One I might upgrade too is using a bunch of 72v to 12v DC to DC converters. That way no cells will be in parallel. Then I just need to keep track of temps and volts of each string. So far I only have 35 1.9+Ah cells processed. I can only charge 7 cells at a time, and only test 4 at a time. I get maybe 10 cells a day done. Its about 50% good cells, 35% decent cells, and 15% duds.
 

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.
You could just save up & just buy the LiFePo batteries instead of buying converters & used cells.
 
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