Poor man's 15 Amp battery charger?

Hopefully after the series 12uf cap, and before the (polarised?) electrolytics :mrgreen:
 
bearing said:
If we neglect ESR of the cap, we have the RC constant of the output cap and internal resistance of the battery pack to smoothen the current. The cap will only make a noticeable difference if the RC time is as long as the distance between the pulses from the rectifier, or longer. Pulses come at 100-120 Hz, or about 0.01seconds apart. If battery IR is 0.01 ohm, then the cap needs to be about 1F. If battery IR is 0.1 ohm, then cap needs to be about 0.1F. Thats pretty big caps, especially if they need to be rated 400V.

I think I'll make mine without output caps.
Click to expand...

I see. I didn't do the math. Glad you did it for us.
With really stout cells, the ripple current won't cause any problem that I can see. Who knows, maybe pulse charging the cells might even have some benefit. It's with wimpy cells (high IR) that you could certainly run into issues. By choosing the AC cap so the current is not too high, any heating issues should be avoidable.

Again, I highly recommend using a GFCI and fuses on both AC wires with this kind of charger.
 
Again, I highly recommend using a GFCI and fuses on both AC wires with this kind of charger.
Click to expand...

This is the only GFCI I was able to find for 220V.
http://www.shopatron.com/products/productdetail/part_number=AWP-77B/1754.0?utm_source=google&utm_medium=shopping&utm_campaign=googleshopping

Is there anything cheaper for a poor man?
 
Look for fleabay or garage sale bathroom appliances, hair dryers can have very high power demands (1800+watts) and have good guage cords because of it.

http://www.ebay.com/itm/230664037249
 
Yes, the GFCI units used on hair dryers are the ticket.

Sometimes you can find relatively cheap GFCI receptacles at the local home improvement store. These usually have connections for additional loads on the back so the whole thing can be inside the box.
68dca62b-3af7-4cd1-a2eb-f2c6e54aca92_300.jpg

$12.58 /EA-Each (here in the US, this is the normal plug configuration. In your area, they should sell ones that match your plugs.) You don't need to actually plug into this outlet, you can use the wiring terminals on the back side.

Skippic, in your schematic, I think the power resistors are not necessary. The current will be limited by the AC capacitor. It also seems the output caps are not necessary either.
You might want to power your 5v supply directly from the line too, as the output side voltage could vary over a wide range. A old cell phone charger works well for this.
 
fivari said:
Aren't the electric circuits in your house protected by fuses and GFCI? You could count on those for protection,isn't it?
Click to expand...

My house was built in 1955. No GFCI outlets other than the ones I installed. If your house has these already installed, then yes you could use them, but if you are taking the charger with you for opportunity charging, you never know what you will get.
 
Skippic, in your schematic, I think the power resistors are not necessary. The current will be limited by the AC capacitor. It also seems the output caps are not necessary either.
You might want to power your 5v supply directly from the line too, as the output side voltage could vary over a wide range. A old cell phone charger works well for this.
Click to expand...

I'm using them for now, I get much flatter charging current, but might omit them in the future if anyone confirms, that there really is no damage to the cells in the long run. I remember a Headway charging setup, that did emit sound (not good).

For the 5V I'm using a phone charger, but it also works powered by the battery this way. In the future I intend the charger to be a part of the battery pack and I'll use the Arduino as CA while riding.

Thanks for the hairdryer and wall GFCI suggestions. I hope I'll find a 220V one.

One more question related to the charger, what's the best rectifying bridge to use? The one I have has 2.1V forward voltage and heats up pretty quickly. I looked online for solutions.

http://www.ebay.com/itm/180613576821?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Is this a good idea or is there a rectifying bridge, that would come in one piece?
 
The standard 'cube' bridge rectifiers are going to be the cheapest solution but WILL get hot. A large heat sink is the only solution for that. If you build the thing into an aluminum box, the box can be the heat sink.

I'm not sure if they make Schottky bridges like that. Usually they are dual, common cathode packages, which only gives you half a bridge. You could make your own bridge from 4 of them, but I think you'd still want a heat sink. Since these types are not isolated like the big bridges, you need to use isolated heat sink insulators.

A small fan might be another cheap option. It could possibly run off your 5v supply.
 
If you are having major heat problems I would be using (as fetcher suggested) shottky diodes.
 
bearing said:
Are there any schottky diodes capable of mains voltage?
Click to expand...
I've never found any, but didn't look too hard. Most of them are not rated high enough. Ones that are tend to be quite expensive. Making it out of individual diodes is probably cheaper, but more work. Even with Schottky diodes, you'll still need to dissipate some heat. It might be half. A 20W rated heat sink and a regular bridge will be much more economical.
 
fechter said:
bearing said:
Are there any schottky diodes capable of mains voltage?
Click to expand...
I've never found any, but didn't look too hard. Most of them are not rated high enough. Ones that are tend to be quite expensive. Making it out of individual diodes is probably cheaper, but more work. Even with Schottky diodes, you'll still need to dissipate some heat. It might be half. A 20W rated heat sink and a regular bridge will be much more economical.
Click to expand...

Are these not good enough?
http://www.ebay.com/itm/180613576821

Are 250V diodes good for rectifying 220V mains?
 
Skippic said:
Are these not good enough?
http://www.ebay.com/itm/180613576821

Are 250V diodes good for rectifying 220V mains?
Click to expand...

No, the peak voltage of 220VAC is above 300V.

Besides, the forward voltage drop of those 250V schottkys is only about 0.1V lower than the diodes in the 50A 1000V bridge.
http://www.onsemi.com/pub_link/Collateral/MBR40250-D.PDF
http://www.farnell.com/datasheets/62557.pdf

If you promise :) to never turn on the charger unless the battery is connected, I guess you could use something like 120V/150V schottkys. But then they will blow if there is a glitch in the connection to the battery.
 
My charger is going to be permanently connected to the battery.

As for the 50A 1000V bridge I must have measured it wrong before or the one on my charger is different. I just put 5A through a spare one and the voltage drop was 0.8V and dropping with temperature.

Therefore there is absolutely no reason to mess with Schottky diodes ;)
 
Here's what i'm using for a bridge rectifier:
http://www.newark.com/jsp/search/productdetail.jsp?SKU=51T1788&CMP=AFC-GB100000001

Here's the caps I have paralleled:
http://www.amazon.com/gp/aw/d/B005FUXGZG/ref=redir_mdp_mobile

And I have a 6p 2s group of these caps on the output:
http://www.allelectronics.com/make-a-store/item/EC-2027/2700_Uf_200_V_CapACitor/1.html

I can't get you any pics as i'm at a robotics competition right now (GO 753!) But I have an old and processor heatsink with a fan stuck to the rectifier.
 
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