RECTIFIER WIRING

[2windy]

Looking for some suggestions on wiring my bridge rectifiers up. They are the ones sold here [35amp small square ones with spade terminals]. I'm using 3 of them cause I am bringing[AC] 6 wires down the tower [#10 wire] from my genny. Three seperated coils, 1 bridge for each coil. I am wiring the dc outs of the rectifiers in series for max. voltage. My question is that the biggest wire terminal I can hook to the rectifiers is #10. How do take 30 to 50 volts off these rectifiers to send to my battery bank. Can I just use a short piece of #10 off the bridge and splice it to a larger say #4 or #6 to run to the batteries, or does it even matter what I run to them. I will only be 3 feet away. My genny is 75 feet away. 30 to 50 volts, 20 to 30 amps. Do you think 6 seperate wires of #10 is over kill for this small machine? I love this board. Thanks to all.

[SamoaPower]

To answer your last question first, no, I don't think #10 is overkill. In fact, it's quite a bit on the light side. Since you are running your rectified line outputs in series, all wires will carry the same current. For a line length of 75 feet (150' loop length) and 30 amps, your voltage drop will be 5.4 volts for #10.  Your total line loss would be 5.4 x 30 x 3 = 486 watts. Yeah, WOW! Do you really want to throw that much away? If the tower is 75' from your batteries, I suspect your wire length is even longer.

Personally, I wouldn't use those rectifier bridges but since you apparently have them, I would consider doubling them up. I wouldn't want to run them at more than half their rating. Make sure you have a large enough heatsink that can dissipate 200 watts and keep the case temperature below 50C. Yes, another large loss.

I suggest that you do not use spade connectors to wire the rectifiers. If you see 30 amps very often, you'll burn them up. Solder the wire directly to the bridge lugs and use a piece of heatshrink over the connection to provide strain relief. With the short distance to the battery, #10 should be okay for the interconnects.

[2windy]

Would I be better to put the rectifiers at the genny? Total lenght from genny to batteries is 75 feet.

[SamoaPower]

Sure, it would cut the losses by 67%. Also, #6 or #4 would even be better. You also might consider a compromise and put them at the base of your tower to allow easier maintainence.

[2windy]

Another dumb question is being I am seperating the coils would I still see 30 amps at each coil or the total from all three? When I bench tested it under a load I was getting 40 amps with it wired the way I explained above. I may has confused you.

[Opera House]

If you are using three bridge rectifiers and putting them in series.  I would place at leas 10,000uF on the output of each rectifier.  The peak voltage of each of the windings will happen at the same time.

[2windy]

If you could do it a diagram would help, how would the capacitors help?

[Shadow]

Now I'm confused.. I keep reading where its easier and less losses to transport AC than DC. But now I'm reading where by rectifying at the source and transporting DC you'll have 67% less losses? Or am I missing something here?

[2windy]

So am I. Someone please give us an educated answer to this, DC down the tower or AC down to the rectifiers on the ground. How can you put the rectifiers up on the genny anyway?

[ghurd]

Now I am confused too.

"I'm using 3 of them cause I am bringing[AC] 6 wires down the tower [#10 wire] from my genny. Three seperated coils, 1 bridge for each coil. I am wiring the dc outs of the rectifiers in series for max. voltage."

A 3 phase wired Jerry rigged, then seriesed?

Sounds like it will retain the worst characteristics of delta, star, and probably single phase?

Connecting in star gets more volts more efficiently.  I think.

G-

[SamoaPower]

The reduction in losses of 2windy's set up is because of his series connection of the rectified outputs of three separate phases which forces all six conductors to carry the total load current. For a 75' run, it's the same as having a total wire length of 450'. By having the same current flow in only two wires (150' total), the losses are only one third as much. The situation for a more conventional three phase, three wire hook-up is different since each wire only carries a portion of the total load current.

It has nothing to do with it being AC or DC. By definition, an AC RMS current has the same heating ability as the same value DC current. The wire doesn't care if the current is AC or DC (except for high frequency AC). The loss is the same.

[SamoaPower]

I guess my Electrical Engineering degree and 45 years experience isn't 'educated' enough.

If you want the lowest losses put the rectifiers at or near the alternator. If you want maintainence convenience, put them on the ground.

I don't understand your question about putting rectifiers at the alternator. Almost every car alternator has them internal. Just put them there. Many do.

[Flux]

Shadow

I don't want to discuss the issue of series connected rectifiers as I consider that a means of trying to make something of an unsuitable alternator and that will have more effect than the cable loss.

Concerning a normal 3 phase rectifier used to charge a battery, with an air gap alternators there is no significant inductance. At any instant 2 diodes are conducting, one to the positive line and one to the negative. the dc current is carried by a pair of the ac leads. These change over at intervals, so that each lead carries the dc current for 2/3 of the time.

From the point of view of volt drop, for the same size wire, the volt drop is the same for the ac and the dc case. You can manage with one less wire if you transmit the dc.

If heating of the wires needs to be considered it is different but normally it is volt drop that is the concern.

Flux

[Flux]

If it is producing 40A and the coils are in series, the coils and any connecting leads are all carrying 40A, hence the concern about volt drop if you mount the rectifiers remote from the alternator.

With small alternators, capacitors are often connected across each bridge so that the dc voltage is 3 times the peak of each bridge. At 40A the capacitors will be monsters. Without them you will have a strange vector sum of voltage and I suspect that at any instant one bridge will contribute nothing in terms of volts but the wires will still contribute volt drop.

Flux