120 Volt Charger for Under $100 possible?

Do It Yourself (DIY)
1

Since this is my first post I would like to introduce myself. I am an engineer working in northern Michigan, my degree is in mechainal engineering but I was a mechanic way before I was an engineer. I sand drag race in my spare time, I have a turbocharged VW dragster that goes 90MPH in 300 feet (thats 1/4 of a 1/4 mile) on sand. I have been working on things as long as I can remember and am in need of a new vehicle so I thought about going electric. Just thought I would give some background I know I like knowing who I am talking to and what level of understanding they have.

I have been doing a lot of reseaerch and will start on my first EV conversion soon. My plan is:
S-10 Pickup
Warp 9 motor
120 volt system Ten - 12 volt Exide deep cell batteries
Curtis controller

The question today is about a charger, as you know most chargers for 120 volt system are quite expensive. I had an idea for a charger and wanted to get people’s thoughts on the concept. I read on a windmill forum about taking a 12 volt car alternator and operating it at higher voltages. From what I read it is easy to get 130 volts without hurting them at all
http://islandcastaway.com/stuff/windpower/Alternator%20Secrets.htm
I have seen many 120 volt DC converters to run power tools off your car. You don’t see them as much anymore since inverters and small generators became less expensive, but they were quite popular years ago and worked good.

So my thought is take a GM alternator modified to put out 130 volts and spin it with a 5HP electric motor if I can get 30 to 40 amps that should be comparable to the chargers available and save over $2,000 since I can build it with pieces I alraedy have. I know that it would not condition the battery like an expensive charger will but I thought every couple months I could charge the batteries individually with my small deep cell 12 volt charger.

So any thoughts will it work? Has anyone tired this method?
Tom

2

It could work but I doubt it. For one thing your talking about 5kw. You would need more like 8hp. Good luck finding an alternator that big. Then look at why. You converting a gas truck to run on electricity then charging it with gas. You wouldn’t save any money. You can build your own charger but I would look into building an electric one.

3

Well the output of the alternator could be limited to say 20 amp at 120 volt thats less than 3 KW. My idea is to use an electric motor to spin the alternator not a gas engine but if it works I suppose an ICE could be used to charge the batteries away from home.
As far as big alternators here is one for a semi
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=180252380996&ssPageName=STRK:MEWA:IT&ih=008
Thanks for the response.

4

Okay using an electric motor to turn it. That is a little better but not a whole lot. You still loose a lot in all the different energy conversions. Not to mention the ammount of room it would take. What kind of motor would you use.

5

Just use 120 volt ac line current, run it thru a bridge diode to convert it to AC. Should be way under 100 bucks.

6

put a dimmer on it to limit the voltage… 120VAC is 170V peak to peak… which is a bit high for batteries. If you just put a rectifier on it, you’ll be sorry as soon as you attach it to the pack.

7

[QUOTE=VWBeamer;3532]Just use 120 volt ac line current, run it thru a bridge diode to convert it to AC. Should be way under 100 bucks.

http://www.allaboutcircuits.com/vol_6/chpt_5/6.html[/QUOTE]

You can do that if you want to fry your battery bank

8

How would that fry the battery bank Genius?

120 volts is 120 volts. the peak to peak does not mean anything. Once it is rectified it is 120 volts or slightly less . The result is not any where near 170, did you even look at the circuits with the smoothing cap?

The OP would need to measure his voltage at his house to be sure it was 120. if it was less then he would have to run a smaller battery pack.

The circuit was not meant to be a complete battery charger , it was to show the OP how to get started . he would need a voltage regulator and cut off device for his original plan also.

[B]NEWS FLASH Einstein, every battery charger that plugs in an AC socket works off rectified AC.
[/B]

9

One thing the simple circuit you have does not take into account is voltage/current regulation. Yes I agree you can get DC power by rectifying the 120 volt AC but making a useable charger would be a lot more involved.
Another thing the 60 HZ single phase will give you pulsed DC which the batteries do not like. The alternator will give you 3 phase power at 300 - 400 HZ which when rectified will provide a much smoother DC. The alternator also has regulator built in, it most likely would need modification but may operate as built.

10

[QUOTE=Seafarer12;3436]Okay using an electric motor to turn it. That is a little better but not a whole lot. You still loose a lot in all the different energy conversions. Not to mention the ammount of room it would take. What kind of motor would you use.[/QUOTE]

I got a 5HP 220 Volt motor off an air compressor that should be big enough. From what I read you should charge at about 20 amps 135± volts or about 2,700 watts that would be about 4 HP.

11

[QUOTE=VWBeamer;3540]How would that fry the battery bank Genius?

120 volts is 120 volts. the peak to peak does not mean anything. Once it is rectified it is 120 volts or slightly less . The result is not any where near 170, did you even look at the circuits with the smoothing cap?

The OP would need to measure his voltage at his house to be sure it was 120. if it was less then he would have to run a smaller battery pack.

The circuit was not meant to be a complete battery charger , it was to show the OP how to get started . he would need a voltage regulator and cut off device for his original plan also.

[B]NEWS FLASH Einstein, every battery charger that plugs in an AC socket works off rectified AC.
[/B][/QUOTE]

VWBeamer,
You should check your attitude at the door and learn about AC. 120V is not the Peak to Peak measurement of an AC waveform. It is the RMS or Root Mean Square value that represents the area under the curve. The RMS value is used because it is required in power computations. To get the Peak to Peak value, you must multiply the RMS value by the square root of 2 (1.414). This gives you a peak to peak measurement of 169.7V. This will rectify to 169.7VDC with a small 120Hz ripple. Chargers either transform the AC to a different voltage and then rectify to DC, or they transform/Rectify/PWM the output to control the current going into the batteries.
-enganear

12

[QUOTE=enganear;3569]VWBeamer,
You should check your attitude at the door and learn about AC. 120V is not the Peak to Peak measurement of an AC waveform. It is the RMS or Root Mean Square value that represents the area under the curve. The RMS value is used because it is required in power computations. To get the Peak to Peak value, you must multiply the RMS value by the square root of 2 (1.414). This gives you a peak to peak measurement of 169.7V. This will rectify to 169.7VDC with a small 120Hz ripple. Chargers either transform the AC to a different voltage and then rectify to DC, or they transform/Rectify/PWM the output to control the current going into the batteries.
-enganear[/QUOTE]

actually, it rectifies to half that, its the voltage from peak to 0, not peak to peak. Diodes only let current flow one way, so in a full or half wave, you’d get everything above 0 for a half wave, and for a full wave, everything above, and the inverse of everything below if you use a centertapped transformer.

The voltage would be ~85V, WAY too low for a 120V pack.

You’d need a boost transformer in front of it, something like a 1:1.5 ratio.

he’s right, i think we’re just both thinking 170Vpp would rectify as 170V. It’s half.

Emax = The peak value of the load voltage pulse = 170V

Eavg = 0.637 X Emax (the average load voltage)

Example: The total voltage used to supply a full-wave rectifier is 120 volts. Find the average load voltage (ignore the drop across the diode).

Solution: Since the total secondary voltage (ES) is 120 volts, each diode is supplied one-half of this value, or 60 volts. Because the secondary voltage is an rms value, the peak load voltage is:

Emax = 1.414 X ES

Emax = 1.414 X 60

Emax = 84.84 volts

So when you smooth the wave, its right about 85V with a 120Hz ripple.

http://www.tpub.com/neets/book7/27b.htm

13

You know, you should learn about AC and DC voltage before correcting me,

If you would just read the two links i posted, or even this one-

http://www.kpsec.freeuk.com/powersup.htm#rectifier

You would see that a charger can very easily be built using the circuit and a simple voltage regulator.

Yes, he would need a way to keep from over charging, and yes he may have problems if his AC voltage is a lot less or lot more than 120 volts.

read the links, the out put of a full wave rectifier is RMS voltage!!

I quote “for example 6V RMS AC is rectified to full wave DC of about 4.6V RMS (1.4V is lost in the bridge rectifier)”

So it stands to reason that 120 volt AC rms would rectify to 118.6 DC?

And that with a a smoothing cap, it would bring the DC voltage to around 150?

and with a resister and voltage regulator you could regulate this this to about 138 -144 volts?

and a 120 volt lead acid battery pack has 60 cells, each needs 2.30-2.6 volts to charge. 60 x 2.40 volts = 144volts.

http://www.batteryuniversity.com/partone-13.htm

Where’s the problem, how is this going to kill his battery pack?

As for my attitude, i don’t like to be crapped on, without explanation. The person i was responding just poo ppo’ed my idea, with no explantion of how to help the OP or explain why my idea would not work.

[QUOTE=enganear;3569]VWBeamer,
You should check your attitude at the door and learn about AC. 120V is not the Peak to Peak measurement of an AC waveform. It is the RMS or Root Mean Square value that represents the area under the curve. The RMS value is used because it is required in power computations. To get the Peak to Peak value, you must multiply the RMS value by the square root of 2 (1.414). This gives you a peak to peak measurement of 169.7V. This will rectify to 169.7VDC with a small 120Hz ripple. Chargers either transform the AC to a different voltage and then rectify to DC, or they transform/Rectify/PWM the output to control the current going into the batteries.
-enganear[/QUOTE]

14

Wow, all the bickering. All I can say is it is better to have people think your an ■■■■■ then open your mouth and prove it.

This is a private message I got from VW Beamer,

“Hey, asshat, every battery charger made works off rectified AC, you are an ■■■■■ if think you can’t make a battery charger with a bridge diode.”

I never said you couldn’t do it. All battery chargers use rectified AC if they use an AC source. And by the way it is a bridge rectifier not a bridge diode

Some people need to do a little research before they become self proclaimed experts.

120 volts AC rms is 169.73 peak or 339.46 peak to peak. If you throw a bridge on an extension cord and hook it to a 120v battery bank you will eventually fry it. You need to be able to control the voltage, amperage and shut it off when it is charged.

To VW Beamer What are your qualifications for knowing about this subject?

Mine are 2 degrees, one in Electrical Power Systems, one in Instrumentation and Control. As well as 10 years working in heavy industry 4 of those working for electric utilities in power plants.

15

[QUOTE=Turbotom;3566]I got a 5HP 220 Volt motor off an air compressor that should be big enough. From what I read you should charge at about 20 amps 135± volts or about 2,700 watts that would be about 4 HP.[/QUOTE]

Now that all that is out of the way back to the original topic. I mean if you have all the stuff you can always try it. It will just waste a lot of power. Air compressor motors are no where close to being efficient and aren’t designed for continuous operation. If you ever came accross a 7.5 hp 2 cap 220-240 motor I would rather have something like that. Single phase motors aren’t all that efficient. Three phase would be better but most people don’t have three phase power. If you get all the parts together your next hurdle would be to build a voltage regulator to get 120 volts out of your alternator. It can be done. I have seen it before the only problem is limiting your current. Alternators are set up to maintain voltage no current limiting. You also need to figure out a drive system. The downside to belts is drag. With a high output alternator you would have to have multiple belts or serpentine belt. A chain would be better as far as drag but more vibration, noise, and maint. Direct probably isnt an option because the alternator needs more speed to get full power. Those are just some things that need to be taken into consideration.

16

Sad, really, that you have two degrees and all that experience, but can’t under stand how a rectifier works.

It was arrogance on my part to think i could explain it to you in few simple post here.

[QUOTE=Seafarer12;3588]Wow, all the bickering. All I can say is it is better to have people think your an ■■■■■ then open your mouth and prove it.

This is a private message I got from VW Beamer,

“Hey, asshat, every battery charger made works off rectified AC, you are an ■■■■■ if think you can’t make a battery charger with a bridge diode.”

I never said you couldn’t do it. All battery chargers use rectified AC if they use an AC source. And by the way it is a bridge rectifier not a bridge diode

Some people need to do a little research before they become self proclaimed experts.

120 volts AC rms is 169.73 peak or 339.46 peak to peak. If you throw a bridge on an extension cord and hook it to a 120v battery bank you will eventually fry it. You need to be able to control the voltage, amperage and shut it off when it is charged.

To VW Beamer What are your qualifications for knowing about this subject?

Mine are 2 degrees, one in Electrical Power Systems, one in Instrumentation and Control. As well as 10 years working in heavy industry 4 of those working for electric utilities in power plants.[/QUOTE]

17

My thoughts about chargers are a bit more complicated than you are thinking. The chargers charge until a predetermined charge is attained then they taper off the charge to prevent the batteries from gassing. When they gas they make hydrogen gas which is very flammable and explosive so the goal is to prevent that from happening. Also it is called boiling which also makes you have to add the distilled water more often. This is for wet lead acid Batteries.

18

True, but can you build one for 100 bucks, that is the question.

19

[QUOTE=VWBeamer;3595]Sad, really, that you have two degrees and all that experience, but can’t under stand how a rectifier works.

It was arrogance on my part to think i could explain it to you in few simple post here.[/QUOTE]

I understand them perfectly, I have built halfwave, fullwave, with and without caps and 3 phase rectifiers. Your just mad because you were cocky and came off looking dumb and told a guy to do something that would cook a battery bank. Your plan would overcharge the battery bank and ruin them. Now instead of owning up to it you just insult everyone that tells you, you are wrong. That is sad.

20

Fact

The circiut I posted a link to would put out 150-160 volts DC if 120V AC was inputed.

Fact-

It takes 2.3-2.5 volts per cell to charge a LA battery.

120 volt pack =60 cells. 60 X 2.4 = 144 volts.

Any charger will require a voltage regulator, or do as suggested and use a light dimmer switch on the front side of the circuit and dail in any voltage you wish.