Mixing of Solar Pannels

G'day Robin,

I have a PL20 and use almost all of its internal features. I don't have any issues at all. Frankly I don't understand your final paragraph because if you set up the low voltage cutout for your load, there will always be sufficient supply to run the PL20.

It was a bit of a pain setting up theRS232 interface for the PC but I got there in the end. Had nothing to do with backup battery or internal clock though.

What circumstance were you thinking about where you would not be able to use the internal features?

Hi Rus or Sue

Its been a long time since I have seen a product with no battery backup on its clock but if your familiar with product then you may know that they state that the expansion board is required to fully implement its 6 internal functions.

However they did not proceed with development of expansion board , and its a little hard to work out which are and aren't as reference documents make "interesting reading" and if you say, try and set the time while your experimenting and go one step over your time you have to press the set button 250 times to get back to where you are because it only counts decimal time and in one direction due to its single button operation.

I'm trying for instance to have something turn off for a few hours after midnight
and while this can be done , it appears not compatiable with the low battery volts disconnect function.

I.E. Under some conditions you can have one or the other but not both.

If you have an easy solution to this I'd love to know

Robin Miller

G'day again Robin,

I guess it depends on what you call easy. I have set my PL20 up to be programmable from my laptop. It works a treat and means that I simply set the value I want, press a button and the PL is updated. Real easy.

The hard part was getting it going in the first place - took several hours and several tries at configuring the interface cord, but now it works well.

Reply to me if you would like any info on how to set this up.

Cheers

Russ.

yeah but if the voltage is out of phase couldn't there be some negative feedback resulting in some smoke. ?

Black Shoe,

As far as i know (AFAIK), there is no 'phase' issue with DC.

There is with AC.

But as in the OP, there will be no problem at all connecting different brands and watts together - as long as the Solar regulator can handle the watts.

Cheers Alan.

Hi Blackshoe,

PV voltage is DC so has no phase. If you mean reverse polarity then the regulator will need some sort of internal protection to protect itself as the panel is the source and not the load so will not care. Even if you short a panels +&- leads together it will not blow/kill/destroy itself.

Panels (should) have diodes across the panels outputs (within the junction box) that both allow no voltage to be dissipated back into the panel when dark (blocking diode) and also thermal destruction caused by partial shading or cell damaged (bypass diode).

I have seen the panels voltage get to less than 2V trying to charge a series/parallel bank of 6V 225AHr batteries in one of our repeater trailers.

Regards
David

quickie;
how are you going to mount the two panels, as in, side by side or end to end etc.

Do they both have to be the same length or width ??
Are they going on to the roof of a vehicle or a caravan etc ??

Mainey...

G'day Chris,

Your set up will pretty much end up being the same (electrically) as what we have. We have a 40W and 50W Waeco and run the 50W as a freezer. We have two Sharp 123W panels that I carry on top of the Kimberley Kamper when travelling and lay on the ground when I get to our destination. We have 300AH of AGM batteries and this set-up enables us to go indefinitely without the need for a 240Volt supply.

I have found that I needed a 15 metre cable to get the panels far enough away from the camper to get them out of any shadows from trees, the camper itself and so on. To avoid volt drop I used 13 sq mm cables. I have also found that to get a really good charge into the batteries it is best to change the angle that the panels are facing about three times during the day if possible. I set them up at about 7AM, then change them again at around noon and again at around 3PM. (This is only if we are at the camp of course, otherwise I just leave them facing North if we are going away for the day.)

By doing this my batteries are usually on float by around 2 PM and I use the spare capacity available in the afternoon to run my water pumps and any 240 Volt gear through the inverter. (You know, battery chargers for cameras, phones, torches etc and about once a week we run a Lemair 2.2 kg washing machine.) We also run 12 Volt fluoro and LED lighting.

Our Sharp panels work really well and the Solarex/Sharp combo that you have should perform equally as well. If you use a regulator that keeps track of your charge and discharge AH, the battery voltage and your load and charge Amps you should be OK. These readings assist me to decide when I can run the more demanding electrical equipment.

happy travels
Russ

As the solar panel is a constant current source and the output voltage can be above 18V I thought voltage drop was not a major issue, you can afford to drop 3V from 18V and still be above your charge voltage so I would imagine you wouldn't need 13 sqmm wire.

G'day Chris,

I run a Plasmatronic PL20 as it matches the theoretical 20A maximum out of my two Sharp panels. I use a 200A shunt so that I can include the inverter usage in the overall discharge Amps/AmpHours. The shunt is bi-directional so I have set the battery charger up to charge the batteries via the shunt as well, thus I include the charge current when I have 240V available. I got the shunt kit, complete, from the 12 Volt Shop here in Perth. I can't remember how much it cost.

I also got the PC interface kit while I was at it. This enables me to use the laptop to change settings or monitor the status of the PL20 without having to push the button a million times. It was a bit fiddly to get going but once I had it sussed it was OK. (It was a case of "yeah I knew that" when I finally figured out why it wasn't working.) The PC interface and the shunt can be used simultaneously even though they have a common plug at the PL20 end.

300AH is all the battery I can fit into the camper, but I do have another 50AH second battery in the car that I could use at a pinch. My fridge/freezer combo use about 65AH per 24 hr day - about 22% of my battery capacity. This figure is a little distorted as the fridges are effectively running from the Sun most of the day and only use about 35AH after the panels stop providing energy. I guess realistically my depth of discharge is somwhere between 12% and 20%.

According to my info the batteries I have should last 2500 cycles at that depth of discharge, or about 7.5 years. We will be using batteries nearly all the time when we are travelling as the $4 or $5 we save per night by not needing a powered caravan park site will quickly build up to the point where we will have saved enough to replace the batteries and have money to spare.

None of the above allows for cloudy days and the gradual degradation of the batteries but essentially I have quite a bit of headroom.

To answer your question about the batteries you have, it doesn't make much sense to increase the capacity to charge batteries and then not take advantage of it. And that does introduce a new dilemna. The concensus of opinion among battery manufacturers and the reference material I have read is that all batteries in a battery bank should be of the same age, chemical make-up and condition. While you can add more cells, their internal resistance characteristics will be different.

Even if your batteries appear to be as good as new, the only way you could find out for sure is do a discharge test at, say, the 20 hour rate and see how they really perform.

I worked for a communications company and in the early days the theory was "one out, all out" when it came to dud cells in a battery bank. As time went by and Bean Counters had more influence over how things were done, we started changing individual cells as required. It wasn't an overly successful policy and subjectively I would say that it tended to accelerate the demise of the remaining cells in a bank. (The thing is, were they going to fail anyway? Hard one to prove.)

Certainly good quality AGM batteries are not as expensive as they once were, so if you can afford to replace them, that's what I would do.