solar charging regulators - Page 3 - Electronic Circuits Projects Diagrams Free

nickelflippr · 21st March 2009, 04:29 AM

Still more reading material Maxim AN484 on solar chargers. Buried in the appnote is a paragraph that claims:

Quote:

Applications in which the solar-panel voltage is higher than the fully charged battery voltage demand a step-down converter. As an example of applications demanding a step-down converter, configuring the MAX797 controller as a current source and its internal 5V linear regulator can power the external comparators. The device is well suited for charging a car battery from two 12V solar panels.

So there might be your analog SMPS solution for a smallish < 10A solar array.

Thinking out loud, it would look like a Pic 16HV616 would do the same job as the Maxim797 part. The pic has an internal 5V regulator, a-d, a couple of comparators, and a hardware PWM. Wouldn't a half bridge PWM configuration operate the external mosfet's in the same way the Maxim part does?

P.S. Forgot Max797 pdf

Thunderchild · 21st March 2009, 08:15 AM

but it works with 5 V outout how does that get adapted for 12 volts ? (well 13.5)

nickelflippr · 21st March 2009, 04:16 PM

Quote:

Originally Posted by Thunderchild

but it works with 5 V outout how does that get adapted for 12 volts ? (well 13.5)

Other than taking Maxim's appnote at face value, the datasheet provides a formula for Vout = Vref(1 + R1/R2). So a voltage divider on the output gives feedback to the PWM module to get higher voltages. Also looks like the current loop feedback max is 6V, so that a voltage divider too. There is an example diagram for 8V output.

Its too bad they did not include a schematic for the 12V car battery charger.

Thunderchild · 21st March 2009, 04:56 PM

hm well I'll give the datasheet a good read.

I've just highered the stakes by deciding to go 24 volts straight off. I bought 1 12 volt 44 Ah battery to get me started and then decided to go and try and retreive my old car battery from a mate which was supposed to give it back to me ages ago. so now i have 2 X 12 volt batteries and I expect its quite appropriate to run on a 24 volt system with all the advantages it brings (less amps flying around when things get bigger) and now I'm pretty safe from overcharging the battery as its 1 A/hr max instead of 2 A. I'll still need a charging controller though

**Nigel Goodwin** · 21st March 2009, 06:00 PM

If you're putting batteries in series it's absolutely essential that they are exactly the same make and model of battery, and both in the same condition. Putting random batteries in series is asking for trouble.

Sceadwian · 21st March 2009, 06:13 PM

Ideally they should have sequential serial numbers as well. This may seem silly but it's the best way to make sure they have nearly identical chemistry.

Thunderchild · 21st March 2009, 06:21 PM

oh dear no their not the same one being new and one being out of my deceased car. just how much trouble can it cause ? I would guess they are both of the same type as they're both cheap ones, what about in paralel ?

Sceadwian · 21st March 2009, 06:37 PM

Umm how about sulfuric acid all over the place when your batteries boil over because a couple cells invert or fail, or worse fire. Don't do it. Parallel is almost as bad.

Thunderchild · 21st March 2009, 06:44 PM

ok so why will these things occur ? they are both normal car batteries and will be fed current, what is the greatest danger in charging or discharging ?, I could charge them idividually (1 per panel) but when it comes to using them errrr maybe a switchover circuit if its worth bothering

Sceadwian · 21st March 2009, 06:58 PM

Because over time the plates in a car battery disolve and become uneven, slight boil overs and gassing from normal charging and the byproducts of the charging process also build up causing each cell to charge and discharge at slightly different rates than a new battery. When this imbalance occurs stronger cells will start discharging through weaker cells even if the battery is just sitting there which just further worsens the problem, remember each 12 volt battery is itself 6 smaller cells. You add two packs into the picture and you compound the problem even more especially if they're two batteries from two different cars as they may have different plate structures which will cause there charge and discharge characteristics to be different. Best case scenario is you end up with two dead batteries sooner than you want, worst case scenario is those imbalances are bad enough to cause a cell to boil over and you end up with Sulfuric acid all over the place, and worse it shorts out the other cells and they all boil over too, and start a fire from the large discharge when the whole pack shorts out. Just keep them completely separate.
A good solar charging system isn't gonna do you any good with crap batteries.

Thunderchild · 21st March 2009, 07:11 PM

so its the charging that going to be an issue ? I can charge them seperately one panel per battery.

Basically your saying that by putting them in series I will be forcing one cell to pass more current than it would want because another one wants it so ?? so I take it its not a case of the cell that wants more power will have to make do with what the ones passing less will want.

Do I correctly assume that discharging them in series will not be an issue provising I don't try to take huge currents out and make one work harder than it can ? I could use voltage sensing cicuitry to cut the supply when anyone of the two batteries is getting discharged.

Thunderchild · 21st March 2009, 07:40 PM

if I put the panels in series and the batteries in series but also had a centre "tap" from the battery junction to the panel junction then they would be each individually charged but i would still be able to get 24 volts back for the inverter

nickelflippr · 21st March 2009, 08:06 PM

One word of caution also on the type of battery you bought. Standard auto battery's are just meant to start the car, and that is about it, as the alternator takes over pretty much from there. A deep cycle battery used in marine and Rv applications are constructed with thicker plates? to withstand high depth of discharge. Golf cart battery's are excellent examples of deep cycle-ability and are the gold standard for cost/AH.

Can see the advantages of putting your solar panels in series, but not so much the batteries. With 40W of solar, there isn't enough power to justify a two battery setup. If one had upwards of 100W of solar, then maybe.

The battery life will depend on the energy budget allowed, and how quickly you can recharge between power cycles. One typically limits the discharge cycles to half the rated amp-hour rating of the battery for best longevity. If you consistently blow your energy budget, then an increase in solar and/or battery capacity as required.

Could use the older battery as a practice battery, until you get the charging operation that you are looking for.

Thunderchild · 21st March 2009, 08:11 PM

hm well maybe I'll just return the new battery and use my old one and then invest next in some real batteries (4 X Trojan 6V 220 A) rather than getting more panels next, won't feel the pinch so much if I get my tax rebate (another long story)

nickelflippr · 21st March 2009, 08:23 PM

Took a fella about 5 days of intense southern Baja, Mx sun, to recharge just two 6V Trojan batteries, with a 75W panel. No controller, just direct connect, and no other loads.

The reason behind the 24V volt battery bank again?

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21st March 2009, 08:15 AM	#32
Thunderchild	but it works with 5 V outout how does that get adapted for 12 volts ? (well 13.5) __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) www.simonsphotography.org.uk/ - My other hobby www.rushdenrotaract.org.uk/ - make a difference and have fun ! Never buy "Trust" products, all mine broke !!!

21st March 2009, 04:56 PM	#34
Thunderchild	hm well I'll give the datasheet a good read. I've just highered the stakes by deciding to go 24 volts straight off. I bought 1 12 volt 44 Ah battery to get me started and then decided to go and try and retreive my old car battery from a mate which was supposed to give it back to me ages ago. so now i have 2 X 12 volt batteries and I expect its quite appropriate to run on a 24 volt system with all the advantages it brings (less amps flying around when things get bigger) and now I'm pretty safe from overcharging the battery as its 1 A/hr max instead of 2 A. I'll still need a charging controller though __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) www.simonsphotography.org.uk/ - My other hobby www.rushdenrotaract.org.uk/ - make a difference and have fun ! Never buy "Trust" products, all mine broke !!!

21st March 2009, 06:00 PM	#35
Nigel Goodwin	If you're putting batteries in series it's absolutely essential that they are exactly the same make and model of battery, and both in the same condition. Putting random batteries in series is asking for trouble. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

21st March 2009, 06:13 PM	#36
Sceadwian	Ideally they should have sequential serial numbers as well. This may seem silly but it's the best way to make sure they have nearly identical chemistry. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

21st March 2009, 06:21 PM	#37
Thunderchild	oh dear no their not the same one being new and one being out of my deceased car. just how much trouble can it cause ? I would guess they are both of the same type as they're both cheap ones, what about in paralel ? __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) www.simonsphotography.org.uk/ - My other hobby www.rushdenrotaract.org.uk/ - make a difference and have fun ! Never buy "Trust" products, all mine broke !!!

21st March 2009, 06:37 PM	#38
Sceadwian	Umm how about sulfuric acid all over the place when your batteries boil over because a couple cells invert or fail, or worse fire. Don't do it. Parallel is almost as bad. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

21st March 2009, 06:44 PM	#39
Thunderchild	ok so why will these things occur ? they are both normal car batteries and will be fed current, what is the greatest danger in charging or discharging ?, I could charge them idividually (1 per panel) but when it comes to using them errrr maybe a switchover circuit if its worth bothering __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) www.simonsphotography.org.uk/ - My other hobby www.rushdenrotaract.org.uk/ - make a difference and have fun ! Never buy "Trust" products, all mine broke !!!

21st March 2009, 06:58 PM	#40
Sceadwian	Because over time the plates in a car battery disolve and become uneven, slight boil overs and gassing from normal charging and the byproducts of the charging process also build up causing each cell to charge and discharge at slightly different rates than a new battery. When this imbalance occurs stronger cells will start discharging through weaker cells even if the battery is just sitting there which just further worsens the problem, remember each 12 volt battery is itself 6 smaller cells. You add two packs into the picture and you compound the problem even more especially if they're two batteries from two different cars as they may have different plate structures which will cause there charge and discharge characteristics to be different. Best case scenario is you end up with two dead batteries sooner than you want, worst case scenario is those imbalances are bad enough to cause a cell to boil over and you end up with Sulfuric acid all over the place, and worse it shorts out the other cells and they all boil over too, and start a fire from the large discharge when the whole pack shorts out. Just keep them completely separate. A good solar charging system isn't gonna do you any good with crap batteries. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har." Last edited by Sceadwian; 21st March 2009 at 06:59 PM.

21st March 2009, 07:11 PM	#41
Thunderchild	so its the charging that going to be an issue ? I can charge them seperately one panel per battery. Basically your saying that by putting them in series I will be forcing one cell to pass more current than it would want because another one wants it so ?? so I take it its not a case of the cell that wants more power will have to make do with what the ones passing less will want. Do I correctly assume that discharging them in series will not be an issue provising I don't try to take huge currents out and make one work harder than it can ? I could use voltage sensing cicuitry to cut the supply when anyone of the two batteries is getting discharged. __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) www.simonsphotography.org.uk/ - My other hobby www.rushdenrotaract.org.uk/ - make a difference and have fun ! Never buy "Trust" products, all mine broke !!!

21st March 2009, 07:40 PM	#42
Thunderchild	if I put the panels in series and the batteries in series but also had a centre "tap" from the battery junction to the panel junction then they would be each individually charged but i would still be able to get 24 volts back for the inverter __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) www.simonsphotography.org.uk/ - My other hobby www.rushdenrotaract.org.uk/ - make a difference and have fun ! Never buy "Trust" products, all mine broke !!!

21st March 2009, 08:06 PM	#43
nickelflippr	One word of caution also on the type of battery you bought. Standard auto battery's are just meant to start the car, and that is about it, as the alternator takes over pretty much from there. A deep cycle battery used in marine and Rv applications are constructed with thicker plates? to withstand high depth of discharge. Golf cart battery's are excellent examples of deep cycle-ability and are the gold standard for cost/AH. Can see the advantages of putting your solar panels in series, but not so much the batteries. With 40W of solar, there isn't enough power to justify a two battery setup. If one had upwards of 100W of solar, then maybe. The battery life will depend on the energy budget allowed, and how quickly you can recharge between power cycles. One typically limits the discharge cycles to half the rated amp-hour rating of the battery for best longevity. If you consistently blow your energy budget, then an increase in solar and/or battery capacity as required. Could use the older battery as a practice battery, until you get the charging operation that you are looking for.

21st March 2009, 08:11 PM	#44
Thunderchild	hm well maybe I'll just return the new battery and use my old one and then invest next in some real batteries (4 X Trojan 6V 220 A) rather than getting more panels next, won't feel the pinch so much if I get my tax rebate (another long story) __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) www.simonsphotography.org.uk/ - My other hobby www.rushdenrotaract.org.uk/ - make a difference and have fun ! Never buy "Trust" products, all mine broke !!!

21st March 2009, 08:23 PM	#45
nickelflippr	Took a fella about 5 days of intense southern Baja, Mx sun, to recharge just two 6V Trojan batteries, with a 75W panel. No controller, just direct connect, and no other loads. The reason behind the 24V volt battery bank again?