# DC Battery Charger?



## Guest (Aug 4, 2011)

If you have a DC output generator then you will need to control the voltage and amperage from the genet before you hook up to your batteries. What voltage are you talking about and what amperage and what battery type are you planning on charging? 

Vague information will not get much in the way of answers. Details man, details.


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## khantroll (Aug 3, 2011)

Sorry about that. Don't really know what I was thinking. 

The system voltage is 156v, made up of 44 Toyota Prius NiMH cells, wired up a little weird. I have 2 strings of 22 in parallel, wired into a junction box creating a parallel connection before they go into the controller. 

Range is going to be pathetic in the beginning, but they were dirt cheap, lighter then Lead Acid, and I have room for more strings. Then again, I am also not discounting the possibility that I'll say screw it and pickup the trusty lead acids. 

The generator that I currently use is custom, designed more as a proof of concept then anything else. There is small hobby motor, 1.5hp with a 10,000 max RPM and running off gasoline, connected via pully and belt to DC electric motor. The label says that it is rated up 120v at 40 amps, but I've never gotten it there. The leads off the motor are run into a regulator and the leads from that come off into spades. There is a 12v deep cycle battery on the same cart all this is bolted to, and it has a set of isolated eyelets around the poles. When it needs charging, I connect the spade connectors and start the engine. The battery also has a 400w inverter clipped to the top of it. On the same cart is a set of three 12v plugs with the same spade connectors. When I don't need to charge the battery, these things are connected to the power leads instead. 

Here is the article that gave me the idea for this: http://theepicenter.com/tow02077.html


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## Guest (Aug 4, 2011)

Be very careful with Prius Batteries. They require special care and charge algorithms to charge them properly. They do not do well charging in parallel. DANGER 

http://greenev.zapto.org/prius/Prius/Prius_Pack.html


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## khantroll (Aug 3, 2011)

Yeah, I know about charging NiMH in parallel. That's why I have the junction box, and no real charger in place right now. The junction box (like in solar installs) isolates the strings from each other (as much as possible). Right now, when I need to charge (which isn't often, because I'm still debugging my home made controller), I drop the tray and charge them individually using notebook chargers based on info at endless-sphere. So far, no boom. Doesn't mean it won't though. 

I've found some DIY chargers that can be set to charge the cells right, but at the moment they wouldn't be cost effective. I'd need one charger per cell, because they are all designed for RC components. I have no problem with one series string if I can come up with a charger that can charge them appropriately fast enough, but I don't think that is possible. 

I will probably be going lead acid in the end, but man, the _weight_. I mean, I am basing this off the TEVan, but I really liked the idea of cutting that weight down a lot. Especially considering a Dodge Caravan is a brick on wheels. 

If I could just find a DC charge controller with a programmable charge cycle, and USB or RS232 input, I could use an arduino to monitor the temperature change in each string, and use the programmable charging cycle to emulate the proper charging of the cells. But the only things I have found that do this A) require AC input, and B) cost about 4 grand.


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## dimitri (May 16, 2008)

khantroll said:


> There is small hobby motor, 1.5hp with a 10,000 max RPM and running off gasoline, connected via pully and belt to DC electric motor. The label says that it is rated up 120v at 40 amps, but I've never gotten it there. [/URL]


Setting aside Ni-MH issues.....you have a 1kW gas engine, so you can't expect to pull more than 1kW from DC motor, in fact likely much less due to efficiency lost in power conversion. Your peak motor rate is 4.8kW, but you have no chance of getting even close to it since you have only 1kW spinning it. DC generator voltage is a function of RPM, so you can get higher voltage and obviously less current if you spin it faster ( perhaps change pulley ratio ). You are still limited to 120V according to motor specs, you can push it somewhat at the risk on blowing it up or burning it out, but you are still far away from your desired 156V for charging, which means you have to boost voltage further, which means more cost/complexity/losses, making whole thing impractical.

If you have skills to rewire your motor for higher voltage output, above your pack voltage, then it might be possible, but you still need some voltage/current regulation to keep battery happy while charging.

Above all, power is power, you not going to get more out than you put in and your 1kW gas engine is a weakest link.


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## valerun (Nov 12, 2010)

Open Source DIY 10kW charger at http://www.diyelectriccar.com/forums/showthread.php/10kw-60a-diy-charger-open-source-59210.html ;-)


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## Guest (Aug 5, 2011)

valerun said:


> Open Source DIY 10kW charger at http://www.diyelectriccar.com/forums/showthread.php/10kw-60a-diy-charger-open-source-59210.html ;-)


We are talking FAST DC to DC charging or at lest I am. Not an AC to DC charger that is 10kw in size. However I am very interested in this charger. I think it is an excellent thing to have. But what I am talking about is direct DC power to Battery and controlled for your battery type. 

Fast High Amperage charging. Like charging in 20 minutes sort of charging with no wall power. 

Since the cats out and running around. 

Pete


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## valerun (Nov 12, 2010)

gottdi said:


> We are talking FAST DC to DC charging or at lest I am. Not an AC to DC charger that is 10kw in size. However I am very interested in this charger. I think it is an excellent thing to have. But what I am talking about is direct DC power to Battery and controlled for your battery type.
> 
> Fast High Amperage charging. Like charging in 20 minutes sort of charging with no wall power.
> 
> ...


can easily adapt. the funny thing is that the main limiting factor in increasing charger power is the inductor. Especially for DC-DC config where you don't need input caps. Jack R suggested to use some of the motor windings as an inductor which might make sense but requires contactors etc...


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## Guest (Aug 5, 2011)

valerun said:


> can easily adapt. the funny thing is that the main limiting factor in increasing charger power is the inductor. Especially for DC-DC config where you don't need input caps. Jack R suggested to use some of the motor windings as an inductor which might make sense but requires contactors etc...


And another limiting factor is the amperage output of the DC source. It is not as much of a limiting factor but still a factor.


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## dtbaker (Jan 5, 2008)

gottdi said:


> We are talking FAST DC to DC charging or at lest I am. ...what I am talking about is direct DC power to Battery and controlled for your battery type.
> 
> Fast High Amperage charging. Like charging in 20 minutes sort of charging with no wall power.


hhhmmmm, you mean like if you had a 'slow-charged' pack of 44 cells sitting ready, with nominal voltage in use at 44*3.2= 140.8v and hooked directly to your depleted pack of 38 cells, where the desired 'finish voltage' is 140.8/38= 3.71v.... then you'd get a very fast charge, wouldn't you? And it would basically be in CV mode and 'finish' without any hardware/software as the smaller pack approaches its finish voltage at the larger pack's nominal operating voltage.

essentially using a slow charged pack as a reservoir capable of a quick dump of energy..... All you'd need would be a monster contactor that wouldn't weld itself on initial contact.


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