solar charging regulators

[nickelflippr]

An interesting thread **broken link removed** May have to rethink whether the MPPT thing is really worth it for one panel.

wombweller said:

Would the solar trickle charger stay connected all the time and if yes does this mean when I connect the load up to the battery it will take the power from both the battery and the solar panel in other words how do we separate the connection so it's only the battery that's being drained?

Yes the solar panel and battery both stay hooked up in a parallel configuration. Your little trickle charger is going to have little effect on a single battery, much less a bank of batteries. Most trickle chargers don't even bother with electronics, or controllers, because there output is so low.

 

[HarveyH42]

Batteries are kind of expensive, and a charge controller is well worth the investment. You can't really know when the battery will get a full charge, sun doesn't always sine the same all day, every day, nor the drain on the battery be the same daily. The charge controller takes care of maintaining the proper charge, and cuts out before it over charges.

 

[Thunderchild]

so I'd have to check the battery voltage now and then and reset the SMPS to just above that.... trick seems to be making a SMPS that can be controlled so easily......

 

[ericgibbs]

hi TC,
This is a solar panel controller using a miniPIC, maybe worth a look thru.

**broken link removed**

 

[Thunderchild]

hm I'm not sure what that circuit is doing ? looks like is just stopping charge when full, I don't see anything that looks like a SMPS voltage reduction.

 

[nickelflippr]

More reading **broken link removed** article. Looks like the ACS712 would work for my 75W panel, and would be easier than the Maxim devices I've sampled (which still require a shunt).

Here is a Microchip appnote on a switchmode? regulator using a PIC 16HV785. The 16HV785 has two op amps, very interesting. Going to have to read read this one a few times to decipher.

 

[Thunderchild]

Would this be a good regulator, unfortunately none of the regulators have proper explanations of their technology

**broken link removed**

 

[nickelflippr]

Would this be a good regulator, unfortunately none of the regulators have proper explanations of their technology

**broken link removed**

Might very well work with flooded lead acid batteries. Without any sort of data sheet it's hard to tell.

For perhaps a little more money? you get a data sheet, from Xantrax, Morningstar, or other well known PWM controller mfr. Included would be a 3 stage battery charger, plus equalization charge (if required). Also, you usually get a selection for battery chemistry, flooded, agm, gel or a variable setpoint voltage.

Here's a **broken link removed** link with an atmel controller.

 

[bryan1]

G'day Thunder,
All I use in my shed for my main 700ah battery bank is a LM358 based shunt controller. The output is 2 169amp fets in parrallel and they dump 18 amps into a heat based dumpload. I went for the bigger fets as I kept blowing boards up when my wind gennie maxed out. It's a simple circuit that works on most voltages by simply changing a few resistors and if you want it just singout and i can email it to you.

As far as open circuit on PV panels dont worry about it as soon as you hook them upto a battery the voltage will drop to the battery voltage. Most commercial PV charge controllers simply short out the pv panels when the battery is charged which personally I consider a waste of energy.

Cheers Bryan

 

[Thunderchild]

HI Brian, well from what you say you are just switching the panels on and off when the battery charges, what I'm tring to do is adapted the panels power to the battery as best as possible so as to get the most out of them. will the panel automatically output more current when less voltage is required ? I don't think so in which case power is being lst, hence me wanting a SMPS/PWM controller

 

[nickelflippr]

Still more reading material **broken link removed** on solar chargers. Buried in the appnote is a paragraph that claims:

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]

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

 

[nickelflippr]

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]

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]

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]

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]

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]

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]

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]

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.