diy solar

diy solar

Heat sink question

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xhdskip

New Member
Joined
Apr 29, 2021
Messages
51
To those more knowledgeable than myself, I have a question.
I have 4 Blocking Diodes, mounted to 1 heat sink.
4 holes drilled into 1 single 2" piece of Aluminum square tubing.
That way my "in" is at the top and the "out" comes from inside the tubing.
My question is this, since the flow is out from all 4 wired touching the same piece of alunimum,
will they short out?
if so I can cut them apart, if not, I'll leave it like it is.
Thank you.
skip
 
Would depend if the diodes' mounting surface have galvanic isolation. If not could use mica or a sil-pad between device and the heatsink.
 
they're from Missouri wind and solar, they've got a youtube video,
I bought them off Amazon though.
just metal to metal it looks like to me.
 
Trying to get the pics I just took to my email. If someone could text me,
I'll send them to you if you could attach them here in the thread, I'd appreciate it.
My cell number is (removed by admin)
Thanks I'll keep working on trying to upload them.
 
Last edited by a moderator:
To anyone with a similar problem in the future,
I just spoke with the tech at M.......wind and solar.
He said do not put the cable ends directly to the metal (like I did)
use the nut provided to tighten the diode down, then the cable end, then another nut to secure the cable.
The voltage passes through the diode internally.
Don't make alot of sence to me as it's all metal, but that's what he said.
Thanks for the help guys, if I learn anything else, I'll post it...
THANKS AGAIN
 
Finally figured out a way to post pictures to my desktop.
Here is what I HAD.Diode heat sink 1.png
 
The next pictures won't look like this as I decided NOT to take the techs advice.
He seemed to be in a hurry, and I'm not sure he understood what I meant or was talking about,
so I let my gut lead me. I unhooked all the diodes, cut the aluminum heat sink into 4 semi equal parts,
rehooked the diodes, and eliminated the possibility of any shorts,
as now two are on one side, and two are on the other, spaced about 6" apart,
and 4 foot for the other two, which are again, about 6" apart.
 
How big are the arrays you use blocking diodes on?

Also, when operational, have you measured heat loss?

Curious f you think it’s worth it.

Will did a video and found a couple wats loss on each diode. Makes sense a larger array would make more loss requiring heat sink.

Blocking diodes are generally considered not worth it on this forum. I don’t have them on my three arrays I built, and the two sets of 4s3p arrays an my roof the contractors installed don’t have them.

Edit: with the way these are wired I understand your concern about shorting to the aluminum.

Edit: also looks odd the way the circuit breakers are ganged together. In addition to them being ganged at all, appears ganged with two open and two shut.
 
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Q-Dog said:
Can someone explain what problem these diodes are trying to solve?
Click to expand...
They can only solve the problem of current flowing in the direction you don't want ;)... So being a solar forum, I'm guessing to allow a battery to charge when there is sun and not discharge through solar panels when the sun goes in.

But who knows? As there are 4 of them, maybe he's building a massive rectifier for his 2000W HiFi system's power supply? ?
 
Most stud packaged rectifiers have the case as cathode of diode. You will need thermal conducting insulator bushings for common heating sink mounting,

You will have 0.8-1.1 volt drop across regular silicon diode depending on current level so can get a lot of heating to dissipate for high currents.

At high current, hot-carrier Shockley diodes are not much better for voltage drop since they have a greater series resistance than regular silicon diodes that adds voltage drop to their lower conduction voltage point. Their use is usually when high frequency fast switching recovery time needed.
 
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Schottky diodes also have high reverse-polarity leakage. Can also get into thermal runaway and short out - an engineering analysis of data sheet parameters and curves is needed to figure that out.

Schottky is fast, but there are also fast silicon junction diodes. And slow ones.

Yes, those stud rectifiers have case as one terminal. Would have to be mounted in a manner that provided electrical isolation (if desired) and thermal conductivity. I don't think there is a proper method to do so for this package - you don't want compression of a soft insulator to be what maintains electrical contact. They are normally used with heatsink electrically hot.

"Blocking diodes" - what for?
Rectifying diodes for an alternator make sense, and we tolerate the losses. For SMPS, Mosfets are used to reduce the loss.
If for PV strings, I don't believe diodes are needed, only cause some loss.
 
PV cells are forward-biased diodes, so that would be in the conducting direction at night.
But with the exponential I/V curve, a PV string with Vmp high enough to charge battery would have relatively low discharge at night. It might add up to something for a large array, or many nights.

Diodes could help in that case, would drop voltage by 2 or 3 PV cells worth. An "ideal diode" would be better.
A PWM charge controller would be the correct thing to use, otherwise battery would get cooked if PV array was big enough to do much good.
 
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