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Forum Index : Solar : Experimental Multi-Phase Solar MPPT Controller
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Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138
Posted: 12:57am 29 Dec 2019
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Hi Tony, Our system is not well matched, PV voltages are approx 3 x the nominal 48v battery voltage, so duty cycles are approx 30%, making the use of a synchronous mosfet somewhat more efficient than a schottky rectifier because of the high current short duration pulses.
I agree once in absorb and float modes charge currents taper off, and using synchronous rectification is a somewhat wasted over complication. But we have some large water pumps\motors that run for extended periods, so even in float mode PV load currents will be very high at times; although current sharing via the multiple phases per controller will reduce the power dissipation somewhat.
As I'm building 7 of these controllers, will make one substituting schottky diodes and do a comparison, I have some TO-247 diodes so can just replace the synchronous mosfet and cut the existing track to the gate.
Cheers Mike
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 02:47am 29 Dec 2019
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Fair enough Mike, I did not realise you were stepping the voltage down quite so low.
At 25% to 30% duty cycle, that is about the worst duty cycle for diode dissipation, so a synchronous rectifier will definitely be the way to go.Cheers, Tony.
Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138
Posted: 07:49am 30 Dec 2019
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For PV input voltages in the 70-100 volt range, it maybe worth creating another version of this design minus the specialized half bridge driver chip and supporting components; and to use a schottky rectifier in a non-synchronous arrangement.
With the current pcb layout of the power modules, I'm not that happy with it, there is too much compromise in breaking up the high current tracks to allow the driver components , I would prefer the mosfet driving components be mounted on a separate pcb module that is mounted vertically soldered direct to the mosfet pins, leaving the high current traces with a better layout.
So will create version 4 whilst waiting for the other lot to come back from China.
Edit: Here is the synchronous driver module that I'm thinking of using, sits directly on top of mosfet pins.
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Cheers Mike Edited 2019-12-30 21:03 by Solar Mike
Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138
Posted: 03:57am 04 Jan 2020
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Version 4.1 mppt power module has been designed to accommodate either a fully synchronous mosfet or use of a schottky rectifier. Now that the driver electronics are on a separate pcb (50x40mm) the high current paths on the power board can be better optimized.
Have also made provision for different sizes of electrolytic caps.
Here is the revised driver pcb, this one for synchronous rectification, will do another for non-sync using a schottky dual rectifier (ver 4.1N pcb); the pcb slides over the mosfets gate\source leads and sits vertically above the 2 mosfets.
For non-synchronous, these high voltage schottky's are expensive, costing more than a mosfet - especially if you want one with a low forward voltage drop in the 30-40A region, so its a moot point if its worth the effort in using them, the fancy half bridge driver chip can be replaced by cheaper items, so cost will be similar.
Will do the other driver module and get this off prior to Chinese NY.
Cheers Mike
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 04:20am 04 Jan 2020
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Looking really good there Mike. I will be really interested to see how this all goes.Cheers, Tony.
Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138
Posted: 10:50am 05 Jan 2020
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I hope this never ending saga will end in something that others can build soon...
Here is the schematic for the Schottky version of the power module. the driver PCB components are located to the left of the line. Decided to use a dual 2 input schmitt trigger Nand gate to drive the opto, and provide an inhibit input. The main host controller pcb doesn't have enough drive to run 10-12mA required by the opto mosfet driver; those little Nand gate buffer chips can output 24mA or so, plus the schmitt trigger input coupled with a HF noise filter should keep the crap out off the drive ribbon cable.
There are better isolated mosfet driver chips around now than the FOD3182, that have an inhibit input, run from 5-15v on the input but normal logic compatible, trouble no one in NZ sells them, getting a couple from DigiKey have a $26 postage cost, would have made the design easier though...
I'm not sold on the use of schottky rectifier here, they cost way more than a mosfet and have a voltage drop of about 900mV, so even at 20 amps that's quite a lot of heat generated; but as Warp has suggested, be ok at lower PV input voltages where their On time % is minimal.
Cheers Mike
Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138
Posted: 10:58am 11 Jan 2020
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Found the best source of driver chips required for this project is the Texas Instruments store, shipping is only $9 odd; so have ordered enough chips to make several 4 phase controllers. Pity none of the main suppliers here in NZ, Aussie, UK have them, or if they do they are the wrong version or on back order next 3 months or no delivery time frame.
Now that I can obtain the more modern drivers, have decided to ditch the FOD series Opto's in any new designs and replace with the UCC5350 versions. Makes the circuit simpler and have much higher drive capability.
Here is the updated schematic for the Schottky power module, using the newer driver.
Cheers Mike
Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138
Posted: 05:09am 13 Jan 2020
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Here is the schottky version of the mosfet driver module, the power rail pins also act as heat sinking for the driver chip, thus the large copper thermal areas.
Have just sent all gerbers away, hopefully get boards back prior to start of Chinese holidays.
Cheers Mike
Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138
Posted: 12:09am 05 May 2020
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In light of the work done recently on the 100v mppt charge controller, I will create another synchronous driver module containing the dedicated IR11672AS IC, using this chip has some advantages in that the software is less complicated.
Cheers Mike
Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138
Posted: 10:45am 07 May 2020
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New experimental synchronous driver module for the 4-Phase design, as Im sending off a new order and with the high cost of courier, makes sense to get as many of these small pcb's done at the same time. No idea if this will work, in theory it should, haven't blown anything up yet.... PCB is cut in half to make two drivers each 50x41mm
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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