# rectifier only



## nimblemotors (Oct 1, 2010)

When you rectify 110 vac what voltage do you get? (i'm asking the OP, not you doug..)


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## bwjunkie (Jul 31, 2013)

It won't be a fixed voltage, but fluctuating still, and will drop a lot with a load. Is that the answer you want?


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## nimblemotors (Oct 1, 2010)

bwjunkie said:


> It won't be a fixed voltage, but fluctuating still, and will drop a lot with a load. Is that the answer you want?


What is the voltage at 'low load', like when the battery is almost fully charged?


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## dcb (Dec 5, 2009)

fascinating, folks have done it @ 144v (PB assumed),
http://www.diyelectriccar.com/forums/showthread.php/evdl-charging-off-110-volts-110-17270.html

using a long e*xtens*ion cord for extra resistance. They call 'em "stench cords" cuz they get hot and stink, lol. 96v is probably way overdoing it (as if melting extension cords by design isn't).


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## Russco (Dec 23, 2008)

bwjunkie said:


> Can a 96v pack be charged from 110v AC rectified to DC with no transformers?
> 
> -josh


Rectifier only works just right with a 120 volt pack.  A 96 volt pack will draw WAY too much current.


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## Sunking (Aug 10, 2009)

bwjunkie said:


> Can a 96v pack be charged from 110v AC rectified to DC with no transformers?


No. 

First note in the USA nominal single phase is 240/120, and If I were going to do this would use 240 volts using switch mode to convert.

Anyway to figure maximum output AC voltage using full wave bridge circuit DC = AC RMS x .9.

I took a shortcut because the actual formula is [AC RMS x 1.414] x .637 = DC out. 1.414 x .637 = .9. Gets you the same result easier. 

So at 120 AC RMS gets you 108 DC out max without load. Problem is a 96 volt battery needs 120 volts DC source. Back to a 240 volt Switch Mode Rectifier. 

*Note:* rectifying line AC current direct is a dangerous game.


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## Coulomb (Apr 22, 2009)

Sunking said:


> Anyway to figure maximum output AC voltage using full wave bridge circuit DC = AC RMS x .9.


No, that would be the average voltage. It will vary from zero to around 170 V. So that's why you need something to drop the extra voltage. A long extension cord will do a very rough job of it, with a 144 V nominal pack. A capacitor bank will do better (much lower losses), but it's still really rough and hard on the power system.


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## dougingraham (Jul 26, 2011)

nimblemotors said:


> When you rectify 110 vac what voltage do you get? (i'm asking the OP, not you doug..)


You thought I would answer this? Since it has already been sort of answered can I elaborate on the answer?

AC voltage * 1.414 (SQRT(2)) will give the rectified peak DC voltage excluding the diode drop in the bridge. This would be the highest voltage a pack could be charged to at a current approaching zero with just a rectifier. You can build a voltage doubler with a couple of good size caps that get you almost double this voltage. Without a transformer, some other form of voltage reduction would need to be used or excessive currents will be encountered. I would not recommend this as an approach to charging batteries for a lot of reasons but the greatest is efficiency.

110VAC * 1.414 = 155.6 volts dc

156 volts - 96 volts is a difference of 60 volts. If you want to charge at only one amp then you need a resistance of about 60 ohms. The amount of heat will be 60 watts waste. The amount of energy going into the battery will be 96 watts. Total efficiency will be 62%. The resistor would need to survive 60 watts. Lets say you wanted 10 amps. This would require about a 6 ohm resistor. The waste heat in the resistor would be 600 watts

There is a quite a little more to it than this because of the pulsed nature of the DC. Actual currents would be less than this but this gives you an idea of how bad this could be.


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## dcb (Dec 5, 2009)

Just thinking about this a bit more, I don't think the tesla "superchargers" are doing much more than rectifying 3 phase 480v before hitting the batteries (admittedly rectified 3 phase is a lot easier to deal with). Though it does have some pre-defined load balance levels (60kw/60kw,90kw/30kw).

Dunno. Teslas have good thermal management on their batteries though (and so they are really gonna push quick charging in the marketplace too).

http://www.teslamotors.com/forum/forums/updated-how-it-works-supercharger-station

edit, it says they have 10 model S "rectifiers" per cabinet, not exactly sure what that means.


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## dougingraham (Jul 26, 2011)

dcb said:


> Just thinking about this a bit more, I don't think the tesla "superchargers" are doing much more than rectifying 3 phase 480v before hitting the batteries (admittedly rectified 3 phase is a lot easier to deal with). Though it does have some pre-defined load balance levels (60kw/60kw,90kw/30kw).
> 
> Dunno. Teslas have good thermal management on their batteries though (and so they are really gonna push quick charging in the marketplace too).
> 
> ...



This is quite off topic but the Tesla charger is a 10kw device that has power factor correction. You can purchase an option where they put two of these in a car for 20kw charging at home. They parallel 10 of these in a supercharge station to make a 100kw equivalent charger. I read somewhere that they were actually upgrading to 12 in parallel and then sharing these between two pillars but I can't find a link to that. 10kw will charge a near dead 85kw pack in about 9 hours. 20kw will do the same in about 4.5 hours. 100kw will do it in about an hour. Even at full tilt we are not talking about high C rate charging of the 18650 cells. At 100kw it is only about a 1.2C rate. If they have 12 paralleled then this could be as high as a 1.4C rate. The cells they are using probably tolerate at least a 2C rate without too much heat production so there is plenty of safety margin especially when you consider that they have an active cooling system. These chargers are not just rectifiers tied across the battery. Even if you balanced them to allow for something like this you couldn't tolerate different input voltages and the heat output from the charger would be horrendous.


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## bwjunkie (Jul 31, 2013)

Coulomb said:


> .... A capacitor bank will do better (much lower losses), but it's still really rough and hard on the power system.


do you mean hard on the battery bank?

My pack actually is 120v, so maybe I can try this. I guess my thought was for some rudimentary 10amp _backup _charging cord from 110v source.

so diodes, a couple capacitors (how big?), 50' extension and a fuse?

-josh


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## dcb (Dec 5, 2009)

Thanks for clarifying, the article called it a "rectifier", and it took me a while to realize they were talking about the tesla S onboard charger (of which I still knew nothing).


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## Coulomb (Apr 22, 2009)

bwjunkie said:


> do you mean hard on the battery bank?


Actually, no, I meant the electricity distribution system.



> My pack actually is 120v, so maybe I can try this. I guess my thought was for some rudimentary 10amp _backup _charging cord from 110v source.


They might be OK as a backup charger.



> So diodes, a couple capacitors (how big?),


Hulking big. Large soup cans, multiples of.

See this thread: http://www.diyelectriccar.com/forums/showthread.php/variable-voltage-battery-charger-48691.html

Edit: actually, not necessarily that big:


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## bwjunkie (Jul 31, 2013)

Area you are implying I can roll some aluminum foil and plastic wrap (Saran) into an empty soup can and be done? 

I see now I didn't need to create a new thread this, thanks for all the good info though.

josh


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## palmer_md (Jul 22, 2011)

no, the soup is for keeping you nourished while you wait for the tow truck to pick you up after you ran out of charge and your charger does not work.


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## bwjunkie (Jul 31, 2013)

that is the whole point, to have a backup charger when my expensive one stops working for some reason (probably related to digital comm). so then soup can rescues CAN! 

but I'm not actually going to roll my own capacitor 

-josh


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## Coulomb (Apr 22, 2009)

bwjunkie said:


> but I'm not actually going to roll my own capacitor


I hope the details are in that thread. You can probably use motor run or start capacitors, which are readily available and relatively cheap. Something like 8-25 uF, at least 400 V working, get them from Digi-Key or perhaps even your local electrical retailer. Ebay should have them cheaply.


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## bwjunkie (Jul 31, 2013)

thanks Coulomb, yes I think Run capacitors were mentioned, which is what I have here (hopefully) along with some new rectifiers, total was $30.










and with b&w Cat for sizing and contrast 










I already have a donor extension cord, so we shall see how this goes. I think I'll try just one cap first to see if I get a small current charge, then maybe add the second one. I got two rectifiers only for good luck.

-josh


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