Diodes and bypass diodes

[martinjsto]

I will go back to the first circuit and try to nut it out.
with the video, as the load increased the amps increases . on one gage it was about 6 amps the other about 4 amps, is one before the diode and the other after showing the power used by the diode?
sorry for some silly questions, circuit design was not part of appliance repairs, remove and replace is the norm.
from all the research i have been doing the reccomendation is for only 2 bypass diodes for a 36 cell panel protecting 18 cells each which would be easy to wire. do you agree that 3 is overboard?
if so i will make it with 2.
i have 5, 2 legged inline diodes, 3 from the new cells i purchased and 2 from an old panel. they are only 10 amp each, i might use them in the next panel
is there a way of joining them together to get 20amp or does it always halve the value irrelevant of the way you join them?
thanks again.
have not heard from longwolf for a while, how are your panels going? did you figure out the best arangement for your diode's and how is it working on the van?

[RifRaf]

yes the video is not clear, will redo it it tomorrow in daylight, the shadow from the light was making it look like 6a, both needles are actually equal at 4.5a max. each meter is connected as close as possible to the diode output, no wires etc. the rest of the wiring is rated at 25A+ so there is not much resistance. both diodes are matched, they share they same thermal sensor, unless someone can show me other results will keep using them and feel more confident than by using cheap 8A power diode supplied with certain cells

[john p]

Rif raf something to be careful with all junctions in either diodes or transistors have a design limit of about 90 deg c,, if that is exceeded the lifespan of the device will be very short.. As you cant measure the junction temp you have to allow about 15 deg c less for outer case temp..
Sure you can take them above that temp but they will soon fail.
For long happy life of all electronic components a max case temp should not exceed 65 deg c .. if taken above 110 deg c usually all the smoke inside them gets out then they stop working..

[martinjsto]

hi guys,
i have started a new post to follow my panel construction as i feel i have hyjacked this post enough.

http://www.solarpaneltalk.com/showthread.php?2889-my-first-attempt-at-home-made-panel&p=15376#post15376

will be posting pics of the process for comment and advice.
martin

[RifRaf]

thanks john p, i'll have to base my numbers on the datasheet which clearly state a 175C operating junction temp. got a new temp sensor to check the temps on heatsink etc. the heatsink tabs are also getting extra heatsinking and the diodes will be run at maximum 50% rating. still testing but so far the specs seem up to the task for 8A cell bypass diodes. have taken your advice onboard though hence the testing being done, also received the biggest diodes i could find online today, single inline ones, pretty chunky, need to find proper specs still, so will be comparing against them as well over the next week. you gotta admit that an operating range of -65C to +175C should cover our climate pretty well, from http://www.onsemi.com/pub_link/Colla...R20100CT-D.PDF

[RifRaf]

comparing the MBR20100CT Schottky diode and T10A100L Rectifier diode for use as bypass diodes. these are test results, nothing else apart from the diode ratings. they both cost about $1.50, the first from Jaycar, the second on ebay, postage added a bit more. when these things act as bypass diodes it's normally the early or late sun, lower amps, and then the odd crow or other bird that is brave enough to sit on them in the full sun, so is minimal blocking but i know it matters from testing without bypass diodes

MBR20100CT Schottky Rated for 10A per leg upto 100V DC, Max Junction Temp -65C to +175C, no heatsink
tested at 13V DC, 9A, using a single leg of the TO-220 package
0 minutes, anode temp 25C, after 5 minutes, anode temp 132C
0 minutes, Vf 0.67V, after 5 minutes 0.58V

T10A100L Rectifier Rated for 10A up to 1000V DC, 700V RMS, Max Junction Temp -65C to +150C,
tested at 13V DC, 9A, using the whole diode, no heatsink
0 minutes, anode temp 25C, after 5 minutes, anode temp 174C
0 minutes, Vf 0.82V, after 5 minutes 0.70V

MBR20100CT Schottky Rated for 10A per leg upto 100V DC, Max Junction Temp -65C to +175C, no heatsink
tested at 13V DC, 9.2A, using both legs of the TO-220 package, ammeter showed 4.6A for each leg, bit better than one leg
0 minutes, anode temp 25C, after 5 minutes, anode temp 132C
0 minutes, Vf 0.65V, after 5 minutes 0.53V

sorry for all the numbers but is the same test done 3 times, all the Vf measurements at high temps were stable and not lowering anymore after a few minutes, am now happy to use the 20A TO-220 joined together without resistors, i'd be worried to be using the 10A 700V rectifier diode at 9A though with a measured temp of 174C, with a 150C limit, as sold in the junction boxes and likely in many commercial ones. did not fail though, yet

[martinjsto]

good work RifRaf, thats a realy interesting result, so by using the T10A100L when it exceeding the temp treashhold after 5 min loaded is only asking for trouble especialy if there embedded in the panel, with my current shade issue i wonder how much damage my panels diodes have if they have them inside. and using the two leggs of the MBR20100CT will reduce the amperage per diode by half and experience less vf. looks like a clear winner and we can ditch the resistor
still waiting for my buss wire
that last pic on my cell layout and diode circuit look correct to you? looks like the simplest setup. if so i will be embedding around mid week.

[RonB]

Nice Work Mod

Sorry about the delay. that pictorial, it's not good, try a plain schematic, and go over it yourself, count up the volts as you go, 0V at the ground terminal, 6 series cells should be close to 3v (.5V per cell), and so on to your most positive point. then about every 2.5v, you could place a bypass diode.

Hey time to make a post so I can look at the posted pics!

[russ]

Hi RonB - Welcome to Solar Panel Talk!

Look around all you want and then please join in.

Russ

[solarrules]

Bypass Diodes (Schottky) from Jameco - 100v; 10A; 19 cents in qty

Hello all. What do you think about MBR1100 from Jameco for use as bypass diodes? My panel build is a 6x12 configuration using 6" x 6" (156mm) cells. The specs on this diode say 100 volts and 10 amps.

Due to my 12-cell long configuration, I'd be bypassing 24 cells with each diode (times 3 for the whole panel). Or, at 19 cents each, should I put a bypass diode at each end of the panel?

Jameco url:

http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_312101_-1

Spec sheet:

http://www.jameco.com/Jameco/Products/ProdDS/312101-DS32.pdf

[RifRaf]

solarrules, the diodes will be ok if they are indeed 10A, the datasheet specifies them as only 1A though, which is not suitable at all, so double check on that, 19c seems too cheap for a decent 10A diode

[solarrules]

Another diode

Rifraf,

Good catch. I looked back at my url. Sometimes it states 1A and other times it states 10A. So I'm left wondering which is true....

So I found another one - What do you all think of this? Again, 0.19 if bought in quantity of 100 or more:

http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_618097_-1

Thank you,

[Mike90250]

I can see by the package, that first diode is only 1 Amp cont, may take a 10A surge, but would overheat.

The new diode MBR2535CT , is only good for 35V, so if your array is less than 30V, it should be fine, what is the design amps of your array? Too high and you will have to heat sink the TO-220 package. Look at fig 1 on page 4 of the data sheet, and calculate where your design amps are, take the voltage drop, multiply V * A = watts dissipated

You will only be able to use one diode from each package, but the are a good price. If you know what your shade pattern will be , you can arrange cell wireing/layout, to have the least impact on harvest.

[solarrules]

I intend it to be a 36v 8A panel, but I will have several diodes. At most, I would bypass 24 cells at a time -- about 12 or 13 volts

[Mike90250]

With such huge jumps in voltage, what are you charging / using this for that can still use 24V when it was using 36V ?