PV charge controller - please help

timrobbins

Joined Aug 29, 2009
318
Marshall - he doesn't have fets or opamps. For whatever reason he only has those part groups - and even then I doubt he has much variety per se - so it is all a bit hypothetical I suggest anyway.

If your panel's Isc is less than the float current, and the averaged self-discharge current then connecting a low powered PV panel without a controller is somewhat ok. However, without doing the sizing assessment, it is easy to cook an expensive battery due to overvoltage.

There are a huge number of simple opamp based controllers around to utilise without us dreaming up yet another example. The simplest use a series FET with the battery, to effectively pwm the battery voltage to be acceptable (assisted by the time response of the battery voltage).

Ciao, Tim
 

Potato Pudding

Joined Jun 11, 2010
688
How is the availability of parts in South Africa? I am also still wondering if there are any dead electronics items around to allow more to work with. Give me a broken TV or VCR or even some car parts and I could think up something.

I agree that that first choice is save most of the trouble and look for any of the ICs that can make this much simpler.

I think South Africa should have a reasonable access to materials, even if some areas of Africa would not. But access does not mean affordable or easy.

If the prices are much higher there or the wait times are measured in months then maybe it is worth looking for alternatives.

Even the ICs out of a Fluorescent light ballast might be helpful since those use current control similar to what a battery charger needs.

The brightness and contrast circuit, controlling the beam current in Cathode Ray Tube TVs, might also have some similar elements.

They might not operate at the lower voltages but problems are more often found trying to operate components at too high a voltage than too low.
 

marshallf3

Joined Jul 26, 2010
2,358
Marshall - he doesn't have fets or opamps. For whatever reason he only has those part groups - and even then I doubt he has much variety per se - so it is all a bit hypothetical I suggest anyway.

If your panel's Isc is less than the float current, and the averaged self-discharge current then connecting a low powered PV panel without a controller is somewhat ok. However, without doing the sizing assessment, it is easy to cook an expensive battery due to overvoltage.

There are a huge number of simple opamp based controllers around to utilise without us dreaming up yet another example. The simplest use a series FET with the battery, to effectively pwm the battery voltage to be acceptable (assisted by the time response of the battery voltage).

Ciao, Tim
Well, if he's got the relays and the rectifiers to go across the coils he's also going to need the diodes to control switching the relays in and out.

What worries me is the variations in relay cut in/cut out voltages.

Let's start over by you drawing up a little more straightforward schematic that includes all the components and we''ll work it out from there.

Also didn;'t realize the guy was in Africa, from what I've heard comment parts are next to impossible to find down there and hard to ship in.
 

Thread Starter

Voltaire

Joined Aug 3, 2010
25
How is the availability of parts in South Africa?
:) A friend of mine brought his wife to ZA (South Africa) on his last business trip. When they approached over OR Tambo airport to land she looked out of the porthole and exclaimed "Look! They have roads". He smiled at her and said "Yes dear; and they have Internet too". ZA is miles apart from the rest of Africa in terms of infrastructure and development. We get everything here that you get in the US and Aussie and everywhere else.

BTW Queensland is the best place in the world! No offence Tim, but Melbourne resembles Miami in some ways: quite close to the US - if you know what I mean?!
I used to fly my airplane over the Great Dividing Range to the QLD coast where we holidayed on the Whitsundays. Batfish as big as my torso swam around us in turquoise coral water no more than ten feet deep. Rays skittled the shallows and who knows how many white sharks and irukandji avoided us or swam by us in these tropical, plentiful seas. Ah yes; Australia! The lucky country.

Then there was the mighty Niagara - appropriately entrusted to the mighty nation. As I stood at the feet of Nicola Tesla I was awed by the vision and perseverance of these giants: Tesla, Westinghouse, Bell...
The great monuments in Washington and the madness of NYC. The vastness of industrialized space, observed from 30,000 ft in an A320 that had a bad vibration just aft of the last row of seats. And the unique beauty of the forests in the North. Then there is Texas where it is perfectly legal to drive your arsenal with you in your ute/SUV/truck/bakkie and New Orleans where people (in early 2000s) were too busy partying to take weapons anywhere... :D

Anyway; Africa is poor and there is insufficient electrical energy supply. The reasons for this are poor planning, government consumption, fraud, corruption and a culture of entitlement. The planet is slowly being killed by anthropogenic activity and the more people who can 'go green' the better for the planet. The problem is that these things are expensive and that governments make rules that advantage big business. I started building gray/grey water systems to help poor families save water for their gardens. These are about $1,500 but I managed to get the cost down to $120 by a) building my own trafo-less power supplies ($1.00) b) making my own level switches (usually $20 - $50) out of IP68 casings ($2.50), mercury switches ($0.20) and styrofoam. I wanted to import cheap pumps from China ($10 -$20) but the ZA government considers their tax more important than the planet and it became too expensive in the end.

MISSION: To make green energy available and affordable for everyone.

My mate (because he cares about the planet) is poor and lives in an old house in the outback. His charge regulator is shot and I want to make one that is CHEAP and easy to maintain/repair.

Can you fellas help me?
 

timrobbins

Joined Aug 29, 2009
318
Voltaire - I can't reconcile why you want to use those identified parts, and at the same time indicate you want something cheap.

As Marshall has indicated, relays are relatively expensive compared with say an LM324 and an IRF540 and some resistors. And if you want to make an impact on the environment and economic woes then the PV panel is 99% of all costs, and needs to be reconciled first. Many PV projects have gone through ZA, I have read through ZA reports on many energy related projects in the past, and been involved with one down at Stellenbosch.

A simple series charge controller will be eminently simpler and more cost effective and maintainable and reliable - and if you're keen to make it en masse then it would cost about $5. A little universal project pcb/veroboard and you're almost done. Do you understand how a series controller charges a battery, and have you found any example circuits?

You'll have to spell out your rationale better for wanting to use relays, and wanting to use a shunt control charging scheme!

Ciao, Tim
 

Thread Starter

Voltaire

Joined Aug 3, 2010
25
Thanks Tim
I have some spare parts for this one i.e. a - e above. If you have a better idea for the future or if you think that it would be better to just replace the whole thing with a PCB the I'd be happy to listen.
The circuits I found spend a lot of effort on amp control and this is not necessary in this case. What would you say is the simplest means of achieving the goal? (and cheapest)
 

retched

Joined Dec 5, 2009
5,207
timrobbins said:
A simple series charge controller will be eminently simpler and more cost effective and maintainable and reliable - and if you're keen to make it en masse then it would cost about $5.
He already answered your question. I second his answer.

However, nowadays there are ICs available that monitor your battery condition and your PV array output and buck or boost the output into the battery. This leads to increased harvest by allowing your panel to work in its "Maximum Power Point". It loads up the panel dynamically.. measuring and changing a few times a second in some cases. The reason stuff like this is good, if a leaf falls on your panel and shades 1 cell, it throws EVERYTHING off. regardless of this drop in production, the MPPT circuit will boost the output voltage into the battery to keep the battery charging along with lesser current.

Same thing happens when a cloud passes overhead. It will change load values to put more juice into the battery.

It is very important take battery life into consideration when picking or designing a charge controller.

Read these:
http://circuits.linear.com/339

http://www.ti.com/litv/pdf/slva378
 
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