I just got done rewinding the secondary on a simple battery charger. Now it puts out more amps than the full wave bridge will handle. I am using a radio shack 25 amp 36 volt full wave bridge and the transformer will put out about
30 or 35 amps. This is the biggest full wave bridge they have in stock. Anything bigger means I have to travel a long way and pay a lot more money.My question is this, Can I use two bridges in parallel to handle a higher amperage?
It would be simpler to just not use the power supply at full rated power.of the transformer, which you do not really want to do any way. If you try to use parrellel diodes near their limit one will get hotter than the other and hog the current and possible fail.
That kind of beats the purpose of rewinding the transformer in the first place. I have a hydrgen generator that I am working on and trying to put through some reliability and life expectancy tests. It draws nearley 25 amps and after 40 hours it blew my 25 amp diod and cooked the inductor.. After rewinding the transformer with #10 wire it blew it in a about a minute or so. The fact that it lasted that long tells me that it is not producing much more than the 25 amps so I wouldn't be paralleling them near their limit. That is why I was considering paralleling them.
I know you can parallel the transformers because I used to have an arc welder I built out of rewound microwave oven transformers like this one and paralleled them to increase the amperage. That is where I got the idea of paralleling the diod.
Make one out of four diodes, A quick search sees that a NTE5990 will do around the 45A mark and I believe they are about $4.
Or, the Microsemi MP504W (P/N MP504WMS-ND from Digikey) is rated at
50A/400V and is only $6.40 ea. one-off. It needs an appropriate heat sink.Best regards, Spehro Pefhany
Thanks to both of you for the quick answer. I will check therm both out.
I would recommend that you use four Schottky diodes to build the full bridge rectifier since they are much more efficient (only drops 0.65 volts when conducting than 1.3 volts typical for regular power diodes). At 30 amps, this will save 30 x 0.65 = or nearly 20 watts per each diode and since there are two diode pairs that conduct at the same time, saving will be double or 40 watts.
The Schottky diodes must still be heat-sinked by large heat sink (20 watt is a lot of heat to dissipate) and you might have to find 75V rated Schottky at about 40 amps to get the job done.
Here is a suggestion.
Get Motorola auto diodes. I used them in a high power converter I built way back in 1970 They are capable of very high currents, are cheap and at the time were the fastest powr diodes on the market although they were not advertised as such.
No I have not even thought about them, however I most certainly will and keep that in mind for future reference.
I did finally find a larger full wave bridge which is now working quite well. I wish I had known about this sooner because I have several 100 amp alternators in the shop I could have gotten them from.
Thanks again for the suggestion.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.