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Forum Index : Solar : PV Charge Controller for 100v Battery Bank Designs

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Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 624
Posted: 11:15am 11 May 2020
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Well I still haven't sent those files off. I want to do some more experimentation and have made a more generic module that has these optional functions (129 x 46mm).

1: Synchronous mosfet driver
2: PV Isolation Switch
3: Buck driver

I want to run the mppt section at 62 to 100 Khz, so a better design is needed.

The pcb has the functionality such that the buck driver may have the optional sections simple cut off with tin-snips. In light of the work Poida is doing, the mosfet PV isolation switch may not be required or replaced by a relay. The synchronous rectifier section similarly maybe chopped off if not required and a schottky rectifier used instead. Rather than send off multiple board designs its easier to do it on one.

The buck driver section is always needed and maybe used standalone, I have changed the design of this section to use a modern fully isolated emulated opto type coupler driver, Si8261BBC-C-IS    this version of it has under voltage lockout set at 8 volts and low 2.5//4 amp capability, the chip drives dual ZXG3005E6 10amp drivers positioned directly at the gate of each mosfet. The mosfets used IRFP4668 need quite a high gate current to switch quickly and as I have  at least 50 of those tiny ZXG things, about time they were used.

Here is the PCB, will draw up the schematic to check it.







Cheers
Mike
 
Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 624
Posted: 10:52am 12 May 2020
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Pays to read the manual, drawing up the circuit and checking the spec sheet, the pseudo opto input doesn't like reverse drive voltages in the off state, here is what it expects.


(C) is only good for short wires back to the cpu, (B) is the best, so that's what I have re-done on the more critical buck switch.

Here is the final layout and pcb.




schematic.pdf








Few more items remaining then I can send this lot off and get started on actually building something.

Mike
Edited 2020-05-12 20:55 by Solar Mike
 
Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 624
Posted: 10:06am 22 May 2020
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Well the few more items remaining has expanded some what; after tromping all over my roof armed with a tape measure last week to work out where to put the new PV panels that have now arrived; I'm limited to various series combinations that will fit.
The existing solar thermal hot water panels residing in the center of the roof means the best combinations of PV that will fit are groups of 5 panels in series, so the mppt voltage will be 156v with an upper unloaded value of 192v. Means I need 250v capacitors of which I have none, after re-doing the calculations for the buck converter components I need an input of around 2000 to 3000uf 250v with approx 30 amp ripple rating. The output caps require approx 1500uf with 26 amp ripple.

The previous design needed a few modifications to the pcb to fit the extra components, I have implemented a relay for the PV isolation should that feature be required, or shorted out if not. Added modular plugin pcb's for the double pole analog filters and edge mounted cpu card. The mosfet driver card solders to the pcb pins.

RS sell these 30mm dia 560uf 250v items each with a 5.43 amp ripple rating, so 6 are required for the input.
The output capacitance is better achieved with many smaller items in parallel, These 100uf ones each have a 2amp ripple rating, so 15 in parallel will give me an easy 30 amp and 1500uf. I could have used the bigger 560's but then I would have too much capacitance and the voltage feedback response would be way too slow for stability.

Here is the first cut of the new layout.







Cheers
Mike
 
bob.steel
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Joined: 27/02/2020
Location: United Kingdom
Posts: 27
Posted: 03:06am 23 May 2020
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Over here in the US you cannot work on your own stuff if the DC voltage exceeds about 70 volts I think.
Are you guys allowed to use 100v DC and put it up yourself there? Or do you have to be licenced ?

Thinking of doing a 110v output version later Mike?

This is very interesting and well documented.
Edited 2020-05-23 13:11 by bob.steel
 
Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 624
Posted: 06:19am 23 May 2020
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We have similar rules and regs here, I think if you stacked them in a pile they would be over a meter high, however 100 volts dc isn't an issue here. Everything has to be installed as per some NZ standard regardless of output voltage , lower voltages however don't require an electrical inspection. As a NZ qualified electronics tech who used to work on high power installations where the voltages exceeded 5 KV DC, all this low voltage stuff isn't an issue for me at least, but not recommended for non-qualified members of the public to play with; If in doubt get advice from a suitably qualified electrician.

The output 100v is nominal, my lifepo4 bank floats at 105.6v and peaks at 112v so that's what this controller will be putting out, however as its using 250 vdc output caps, can be made to run at anything below that.

Cheers
Mike
 
Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 624
Posted: 09:33am 25 May 2020
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This has been an interesting exercise, found a couple of issues in the circuit, and made some changes to the keypad connection. Otherwise no errors that I can find. I will have to modify the mosfet synchronous driver card as the driver chip "Drain" voltage sense has a 200v max, so will add a resistive divider.

Here is the bulk of the schematic which I drew up to check the pcb layout, not shown are the actual CPU card details or the 2 charge state output relays, reason I have for using the plugin CPU card is to make it an easy exercise to replace the CPU with another, like one of the "Mite family"





















Cheers
Mike
 
Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 624
Posted: 08:56am 27 May 2020
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Made changes to the generic driver module to allow it to run with > 200 volts input, the synchronous rectifier driver chip IR11672 has a max sense input of 200v, have added a resistive divider to allow in excess of 250v; this change also affects the chip voltage sensing points, but seems ok looking at the spec sheet.

As these drivers have limited current drive of only 2 amps, have implemented supplementary boosters for each mosfet using the ZXGD3005.

Have made the pcb so unwanted optional sections can be simply cut off, rather than designing multiple boards, the cut off bits can also be used standalone. Noting that all mosfets are mounted spaced 28mm apart on the heat sink.






Will make a schematic to check it.


Cheers
Mike
Edited 2020-05-27 19:06 by Solar Mike
 
Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 624
Posted: 11:18am 27 May 2020
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Seems ok.









Mike
 
Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 624
Posted: 04:28am 30 May 2020
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There is always the possibility that the above circuit won't work in the synchronous rectifier part, so have prepared a "Plan B" pcb and will get made at the same time......... just looked at JLCPCB site, only postage option to NZ costs US$35, must be the strife in Hong Kong, seems there is no air post or less expensive courier options any more, this makes small quantities of boards very expensive.








Will check the schematic.


Mike
 
Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 624
Posted: 11:22am 30 May 2020
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No Errors on pcb that I can find: Circuit below.








Mike
 
Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 624
Posted: 01:10am 01 Jun 2020
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Last pcb done, its the low esr ceramic capacitor module, the pcb has 20 x 2 series in parallel to give me a higher voltage rating.

Even good quality electrolytic's dont absorb high frequency spikes, the small module placed across the output caps makes quite a difference to the amount of EMI produced.

I have a reel of 1000 1uf 100v caps and want to continue using them; the 250 volt and above 1uf ceramic caps are expensive, ones on AliExpress are most likely not voltage rated and not recommended here.
Placing them is series has certain advantages if one shorts out, as the other prevents a melt down, when they short they usually burn holes in your pcb as they continue conducting current as they carbonize up. Placing them on a small pcb allows easy removal if this happens.




All gerbers have been sent for manufacture, cannot wait...


Cheers
Mike
 
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