Homestead solar efficiency boost using Schottky Diodes for combining smaller sources into a larger system!
Let's talk Solar! Today I am stepping away from the large assemblies to address one of the unsung heroes of a large solar installation, the combining diode. As your system grows, you will need to parallel multiple sources and batteries together. You can twist wires together, but if there is a problem, it takes down the entire system.
Enter the humble diode, it allows power to flow in one direction only, so if you tie half a dozen cathodes (the negative or banded end) together, the anodes (positive or unbanded side) can be fed from six, isolated batteries. The resulting combination will run your inverters. IF you loose one battery, the other 5 are unaffected by that loss.
Now, let's begin to talk specifics, but before I do, I have no connection to this seller, nor to this manufacturer. The best diode to use is slightly more money, but still inexpensive; it is called a Schottky diode. Schottky diodes are special diodes and have a lot of advantages, however the only one you care about here is the Vf (forward voltage). A Schottky diode has a forward bias voiltage about half of the forward voltage of a normal diode.
Schottky Image from listing:
https://www.ebay.com/itm/24pcs-Vishay-Diode-Schottky-100V-12A-3-Pin-2-Tab-DPAK-International-Rectifier/121073398378?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649
WHY do we care about forward bias voltage? Because we have to make the power we waste here, and if we can reduce that waste, we will have more power overall. Power (watts) is voltage (E for EMF) times current (I in amps) or P=ExI
So, if we have a battery that will supply 100 amps at 12 volts, diode isolated to protect it; we will use Vf (0.7volts) X 100 amps for 70 watts. This will be dissipated as heat, but for this 1200 watts, we only get 1130 watts, because we wasted 70 watts on the isolation.
But if we have the exact same setup with Schottky diodes, we will have this instead:
P = Vf (0.3 volts) X 100 amps = 30 watts and our output is 1170 watts. You will save that same 40 watts 24 / 7 for about a quarter a diode. In the design so far six of these SAchottky diodes will save 240 watts of power for $1.50
This is what the larger current units look like, image from listing:
https://www.ebay.com/itm/Schottky-Diodes-Rectifiers-2X60-Amp-15-Volt-DIODE-MODULE-ISOTOP/273285163944?epid=1718397917&hash=item3fa110aba8:g:cbkAAOSwgd1axcQL
Some things to note here systems vary, and Schottky diodes vary, but selecting them is NOT hard! There are three variables on any diode that are important; past the Vf drop we already addressed.
First is the Reverse Voltage (Vr); this is the voltage the diode can safely block. It should be a minimum of twice the system voltage, but 15 volt for 12 volt is not uncommon.. It can be higher, but the cost goes up at higher voltages, for no benefit.
Second is the most important, and that is current capability. It should be sized for 150% of the expected load, so in the above example a 150 Amp schottky diode is needed. They are available for up to 240 Amps, but the cost increases as you go big.
Third thing to watch is the power dissipation, like we discussed before, that 30 watts has to have somewhere to go, so a heatsink is needed, USE it!
This is on the output, but we need isolation on the input side also, and the same loss calculation applies. The only difference is that the Cathodes go to the batteries, and the anodes tie together; and are common fed by the incoming power source, or sources. The anode always goes to the most positive voltage at every connection.
There is another way to combine batteries, but it is Much more complex. I will address it in another post, but it involves placing power transistors (TMOS Power FET) under the cathode of each battery, and controlling them from a microprocessor.
The Schottky diodes are a simple solution, easily implemented by amateur solar power builders, that will make a homebuilt system run more efficiently! This also allow the homesteader to safely use batteries that are weaker, and to still get some use from them. With diode isolation, you can store more, and have more power available at the homestead!
Very interesting description of how to set up a simple home solar. I had heard of these diodes but didn’t know the details.
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In electronics they have other uses too, but this is the best simple home use.
They used to call them hot carrier diodes, and the were expensive, but they transition fast, so they were initially used in high frequency designs. As technology to make them progressed, their ratings climbed, and their cost fell.
Germanium diodes are also low forward voltages, but they will never handle much power, and the material used is expensive.
I will use fifty 500 watt 24 volt battery banks in parallel to power my off grid house, using solar and wind charging.
The old AC ducts will become my wire race to allow me to add 24 volt wiring for lighting, refrigeration, freezer, and air circulation; directly from the 24 volt batteries.
Happy homesteading, and be blessed!
:)>This is really good information for solar power builders! It makes sense to use battery isolation if you have a multiple battery system.
It is a lot safer, and allows a mix of batteries to be used together. It also lets a single solar panel charge multiple batteries. Diode can be used to combine a solar collector, and a wind generator to charge the same battery bank.
It is common in a backed up system to diode isolate a battery in parallel with a line powered supply. That way, when power fails, the battery automatically powers the device, until power returns; then the line supply takes over again.
Just trying to get the DIY Crowd thinking of ways to save money, while expanding their systems, simply and efficiently.
Glad you enjoyed it! Be Blessed.
:)>Very good information thanks for sharing it :-)
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Any time my friend, Hope it helps you.
Happy homesteading, good luck on your power, and be blessed!
:)>Thank you mate :-)
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I keep forgetting that you are going into winter there. You will need all the power you can get to stay warm. I wish you could send me some cool air, and I could trade for hot, LOL!
G'day mate!
:)>If only it was that easy to trade the air temps. :)
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Amen to that! It would be nice to be able to do that, LOL! We could save a fortune on utilities.
:)>