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Diode for 30A, 15VDC with low voltage drop

I

Ignoramus3585

Jan 1, 1970
0
I am making an electrical box for my trailer. In it, there may be a
battery for supporting a breakaway controller as well as, perhaps, for
driving a 12V winch. Also a solar charger for it.

The box also has a LED light that would light up when the box is
connected to trailer.

Since I do not want the LED light to be on when the trailer is
disconnected (to not drain battery and to not give misleading output),
it needs a diode that does not let current flow "from trailer to truck".

What I would like is to find a low forward voltage drop diode. Specs
on the brake controller call for a 30A fuse, so, to be safe, it would
need to be a 50+A diode.

I would like to know what should work best for this application, is
there a diode with better voltage drop than standard 0.6-0.7 volts.

Can Schottky diodes be used?

thanks
 
I

Ignoramus3585

Jan 1, 1970
0
I looked at some Schottky diodes, and learned that they do not offer
voltage drop that is that much lower than regular diodes. 0.46
vs. o.70, not that a big of a deal.

I have these diodes - Ixys 2X31D40J

http://igor.chudov.com/tmp/ixys.pdf

Can anyone confirm that their current rating is 60A? I am a little
confused, since they are comprised of two parallel diodes, so I am not
sure if their rating in datasheet needs to be doubled or not.

i
 
C

chuck

Jan 1, 1970
0
Ignoramus3585 said:
I am making an electrical box for my trailer. In it, there may be a
battery for supporting a breakaway controller as well as, perhaps, for
driving a 12V winch. Also a solar charger for it.

The box also has a LED light that would light up when the box is
connected to trailer.

Since I do not want the LED light to be on when the trailer is
disconnected (to not drain battery and to not give misleading output),
it needs a diode that does not let current flow "from trailer to truck".

What I would like is to find a low forward voltage drop diode. Specs
on the brake controller call for a 30A fuse, so, to be safe, it would
need to be a 50+A diode.

I would like to know what should work best for this application, is
there a diode with better voltage drop than standard 0.6-0.7 volts.

Can Schottky diodes be used?

thanks

I think the easiest and most bullet-proof solution might be the following.

I assume you are using some kind of connector between the vehicle and
the trailer wiring. You can use a third wire if there is one to power
the LED. Or, you can simply add an additional wire and connector at the
trailer end that connects only to the LED. Sounds confusing, but the
only way the LED will light is if the trailer box is connected to the
vehicle. No power-wasting diode in the circuit. LED cannot light via the
battery in the trailer.

Good luck.

Chuck
 
I

Ignoramus3585

Jan 1, 1970
0
I think the easiest and most bullet-proof solution might be the following.

I assume you are using some kind of connector between the vehicle and
the trailer wiring. You can use a third wire if there is one to power
the LED. Or, you can simply add an additional wire and connector at the
trailer end that connects only to the LED. Sounds confusing, but the
only way the LED will light is if the trailer box is connected to the
vehicle. No power-wasting diode in the circuit. LED cannot light via the
battery in the trailer.

That's true only if the two wires -- one going to led and one going to
the rest of the trailer -- are powered by different cables AND
different plug pins AND are on different relay contacts. Which
unfortunately is not the case for a 4 way trailer plug.

I feel highly apprehensive about putting a diode into that electrical
box, because I do not want something to fail while towing, say, a
heavy load on a hot day and braking on a steep descent (worst case
scenario for brake power use).

Even worst case numbers are not that bad. If, say, these brakes draw
50 A (a number wildly above their actual use or 30A recommended fuse
capacity), continuously, it amounts to only about 35 watts produced.

I have a ultrafast Ixys diode Ixys-APT-2X31D40J, see

http://igor.chudov.com/tmp/ixys.pdf

If I mount it to the back of the electrical box (bolt it to the outer
wall, from inside) and bolt a small heatsink outside, and use heatsink
paste, that ought to be more than enough to safely dissipate those 30
watts.

i
 
J

Jon

Jan 1, 1970
0
That's true only if the two wires -- one going to led and one going to
the rest of the trailer -- are powered by different cables AND
different plug pins AND are on different relay contacts. Which
unfortunately is not the case for a 4 way trailer plug.

I feel highly apprehensive about putting a diode into that electrical
box, because I do not want something to fail while towing, say, a
heavy load on a hot day and braking on a steep descent (worst case
scenario for brake power use).

Even worst case numbers are not that bad. If, say, these brakes draw
50 A (a number wildly above their actual use or 30A recommended fuse
capacity), continuously, it amounts to only about 35 watts produced.

I have a ultrafast Ixys diode Ixys-APT-2X31D40J, see

http://igor.chudov.com/tmp/ixys.pdf

If I mount it to the back of the electrical box (bolt it to the outer
wall, from inside) and bolt a small heatsink outside, and use heatsink
paste, that ought to be more than enough to safely dissipate those 30
watts.

i




- Show quoted text -- Hide quoted text -

- Show quoted text -

Your best bet is a Shottky diode. They have a lower forward drop than
their conventional diode counterparts. See, for example,
http://www.onsemi.com/PowerSolutions/supportDoc.do?type=datasheets&category=815
 
C

chuck

Jan 1, 1970
0
Ignoramus3585 said:
That's true only if the two wires -- one going to led and one going to
the rest of the trailer -- are powered by different cables AND
different plug pins AND are on different relay contacts. Which
unfortunately is not the case for a 4 way trailer plug.

I feel highly apprehensive about putting a diode into that electrical
box, because I do not want something to fail while towing, say, a
heavy load on a hot day and braking on a steep descent (worst case
scenario for brake power use).

Even worst case numbers are not that bad. If, say, these brakes draw
50 A (a number wildly above their actual use or 30A recommended fuse
capacity), continuously, it amounts to only about 35 watts produced.

I have a ultrafast Ixys diode Ixys-APT-2X31D40J, see

http://igor.chudov.com/tmp/ixys.pdf

If I mount it to the back of the electrical box (bolt it to the outer
wall, from inside) and bolt a small heatsink outside, and use heatsink
paste, that ought to be more than enough to safely dissipate those 30
watts.

i

So ty-wrap a #18 insulated wire to your existing cable and add one small
connector at the trailer end.

Alternatively, I don't know how the 4-wire connector is usually wired,
but surely there are other connectors with more than 4 conductors that
you can use.

Chuck
 
B

Boris Mohar

Jan 1, 1970
0
The ones I looked at, had voltage drop of 0.46v or so, which is still
not that much lower than regular diodes. Am I missing anything?

i

Big power mosfet
 
J

Jim Thompson

Jan 1, 1970
0
I am making an electrical box for my trailer. In it, there may be a
battery for supporting a breakaway controller as well as, perhaps, for
driving a 12V winch. Also a solar charger for it.

The box also has a LED light that would light up when the box is
connected to trailer.

Since I do not want the LED light to be on when the trailer is
disconnected (to not drain battery and to not give misleading output),
it needs a diode that does not let current flow "from trailer to truck".

What I would like is to find a low forward voltage drop diode. Specs
on the brake controller call for a 30A fuse, so, to be safe, it would
need to be a 50+A diode.

I would like to know what should work best for this application, is
there a diode with better voltage drop than standard 0.6-0.7 volts.

Can Schottky diodes be used?

thanks

Why don't you take a look at the SED page of my website, at the
several schemes for implementing an ideal diode (or bilateral control)
using power MOSFET's.

...Jim Thompson
 
B

budgie

Jan 1, 1970
0
The ones I looked at, had voltage drop of 0.46v or so, which is still
not that much lower than regular diodes. Am I missing anything?

The Schottky's forward volt drop rises with current, rtaher than being
relatively constant like a normal silicon diode (but youknew that). IMOE the
only way to get lower forward drop is to use a higher rated diode than the
actual load current requires. The greater the over-rating, the lower the drop.
 
E

ehsjr

Jan 1, 1970
0
Ignoramus3585 said:
I am making an electrical box for my trailer. In it, there may be a
battery for supporting a breakaway controller as well as, perhaps, for
driving a 12V winch. Also a solar charger for it.

The box also has a LED light that would light up when the box is
connected to trailer.

Since I do not want the LED light to be on when the trailer is
disconnected (to not drain battery and to not give misleading output),
it needs a diode that does not let current flow "from trailer to truck".

What I would like is to find a low forward voltage drop diode. Specs
on the brake controller call for a 30A fuse, so, to be safe, it would
need to be a 50+A diode.

I would like to know what should work best for this application, is
there a diode with better voltage drop than standard 0.6-0.7 volts.

Can Schottky diodes be used?

thanks

You could use a relay. 20 or 30 amp rated automotive
relays draw about 150 mA, so that's not much burden
on your truck battery, and you wire it so that the
truck ignition must be on to energize the relay.

+ from_truck ---[Relay_in_trailer]---ground


|> |
----+ +-----[Battery_in_Trailer]---

The battery in the trailer is isolated by the relay
contact, unless the truck is on.

Ed
 
C

Christopher Ott

Jan 1, 1970
0
Ignoramus3585 said:
I looked at some Schottky diodes, and learned that they do not offer
voltage drop that is that much lower than regular diodes. 0.46
vs. o.70, not that a big of a deal.

I have these diodes - Ixys 2X31D40J

http://igor.chudov.com/tmp/ixys.pdf

Can anyone confirm that their current rating is 60A? I am a little
confused, since they are comprised of two parallel diodes, so I am not
sure if their rating in datasheet needs to be doubled or not.

i

I would consider that to be a significant difference. 21 watts vs. ~14 watts
for the lower Vf diode.

As a practical matter, I would just use an off-the-shelf battery isolator.
You'll get two diodes and a nice chunky heatsink in one unit. That is
essentially what you're doing anyway - charging two batteries with one
alternator, right?

Chris
 
M

Michael A. Terrell

Jan 1, 1970
0
Ignoramus3585 said:
The ones I looked at, had voltage drop of 0.46v or so, which is still
not that much lower than regular diodes. Am I missing anything?

i



Make it simple by using one of the seven pin (or more) round trailer
connectors made for commercial trailers so you don't need any extra
circuitry. Parallel two contacts on the vehicle side, and run separate
leads to the two loads. It has worked well on tractor - trailer rigs
for decades.



--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
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