Solar Panel Controllers

[JoeC]

I am thinking of getting a 100W flexible solar panel for the Bongo but I am no electrician. Well I think I need 100W !

I have seen 100W kits with a 10A controller and other 100W ones with a 30A controller. Why such a big difference between the controllers? What does the controller do anyway?
Is it worth paying the extra for an MPPT controller?

I have a 75A leisue battery and it will be mainly running the fridge (5A) with the odd LED light inside. Will also use it for USB to charge phones etc.

I know that you are supposed to work out what you will be using to know your total consumption but just doing things roughly.

Thanks
Joe

[g8dhe]

The controllers only come in a couple of sizes, so a 10 A one will be just adequate, remember they can also be used to monitor and control the load as well as the charging, in which case 10 Amp might be a bit on the low side.
The MPPT controllers make better use of low level light as well so expand the time the sun can charge also if you have to park in shade they make a better system.
Flexible panels sealed to the roof can overheat in strong light, you need to allow for cooling or except the reduced output when they get hot.

[Simon Jones]

I've been looking into fitting semi-flexible panel on to mine. This would probably be my controller of choice. It's 20A (200W) and MPPT: http://www.ebay.co.uk/itm/130549038710? ... EBIDX%3AIT

[Tony x]

I have the one as per Simons link and decided on it after a fair bit of research and a strong recommendation from someone who knows a lot about solar panels on a motorhome forum.
A err....'friend', whose name escapes me at the moment, questioned the seller about import charges for the 20A version of which they said their may be some.
On arrival, it was marked as a gift. Lucky friend.
MPPT controllers use a much better system to convert the solar output to something you can use.
I don't expect you get many PWM controllers on those orbiting satellites.

[briwy]

I've been using one of these for about eighteen months without any problems after using the cheapo job that came with the panel failed after a couple of months.

http://www.maplin.co.uk/p/12v-30a-solar ... AoB78P8HAQ

One thing to watch is that they have to be wired to the battery and panel in a certain order or it risks knackering the unit. This seems to apply to most controllers, not just this one.

[g8dhe]

One word about these units they don't meet CE Radio Frequency Interference (RFI) requirements, so don't be too surprised if they cause a lot of additional noise on the radio when working! Its not helped by the fact that you can't screen the PV panels themselves

[Dodgey]

On a 100W panel, a 10Amp regulator (charger) is more than adequate. You'll see 6 amps max with a 100w framed panel and around 5.5amps with a thin panel.

Saying that, all the kits I sell I supply with either:

30Amp PWM (standard) regulator - the 30amps is more about how much current you can pass through the regulator. This does not nescesarily mean solar power. As you can use these regulators as your main power distrubution hub - passing power via your battery to all your appliances. 10Amps is way more than enough for most installations. I use 30Amp ones as that is what you get when you buy regulators with LCD displays. There are no 10 amp ones with an LCD, well , not ones worth buying.

I've had one pack up out of probably 50 so far, and that was because it got damp.

My MPPT chargers (more on that in a minute) are 10Amps. They are 10 amps because, as above, that is more than enough for a 100w panel. You get 40% extra headroom at the panel's full power, AND....... MPPT chargers over 10amps start to get very expensive fast, and they get much larger fast!. I installed 240w of solar panels on a VW T5 recently for a client in London. Money was no object. I talked him out of a 30Amp (390watt) charger when I received it and saw the size of the thing! I installed a 20Amp charger instead (260w). I wired the 2 panels in series producing around 40 volts (remember solar panels are not 12 volts). Higher voltage = less amps, and less cable loss. You can go much higher with voltage using MPPT regulators.

His system is working perfectly and doesn't even get warm.

What is MPPT - I describe it in some detail on my website (soalr camper solutions) at the bottom of the bongo and VW page - but in essence...... PWM (standard) chargers take the voltage from the panel (14-20v) and throw away the excess and provide a little more than your battery has. So if your battery is 11.5 volts. The charger will throw away anything over around 13 volts, and put the rest in the battery as current (amps). On a sunny day, your panel might produce 17 volts (more with flat panels) - so a whole lot of voltage is getting discarded (as heat, the regulator has heat fins on it to discard the heat). Up to 30% on a bright cool day.

MPPT chargers use a big coil and some clever electronics to convert the extra voltage to current (amps) so nothing gets wasted. You get that extra 30% back. This is even more so with thin/flat panels as they tend to have an open voltage of 20-21 volts.

I tested two identical panels with a PWM and an MPPT charger plugged into the same battery and at that moment, the PWM charger produced 0.6 amps an the MPPT charger produced 1 amp (it was an overcast summer day). MPPT chargers do however lose a lot of their advantage on hot bright days, as when solar panels warm up, their voltage drops. This is why they produce 17-21 volts as standard, to allow for voltage drop. On a full-on summers day, I'd expect to see PWM and MPPT produce the almost same current from the same panels. Once it gets cloudy, however, the MPPT charger will leap ahead.

I now sell the vast majority of my kits with MPPT chargers, particularly as they are not much extra.

Oh, for the drool factor, here is the 240w VW installation

[jimmo62]

Just a quick question on using an MPPT controller with a split charge system. Is there any need to do anything special re wiring with both a split charge and a solar MPPT. I assume they both just connect to the battery to charge it and are wired in parallel.

I'm just wondering how the MPPT controller copes with the split charge setup. If the solar cells are not generating and tghe engine is running is there a problem with the split charge circuit powering back into the output of the MPPT? Would you need any diodes for example to prevent current flowing back into the output of the MPPT?

ta

Jim

[Tony x]

There's no need to do anything like put a diode in the wiring. In fact, this would mess things up as the controller may well put out different voltages depending on the voltage it detects on the battery - typically a bulk charge followed by a trickle charge. A diode might prevent it detecting the correct voltage.

Your split charger may cause some issues - which you may consider problems.
If you wire the MPPT output to the leisure battery, then there will be no problems and the solar panel will just charge it without doing anything else unexpected.

If your split charger is voltage sensitive and you connect the MPPT output to the starter battery, which is an option you may want, then the panel will charge both batteries, moving on to the leisure once the starter is charged. If you have one sealed and one open (ie you can add water) battery, then you'll want to set the MPPT output type to that of a sealed battery. If both batteries are of the same type then set the output to that type (basically, you have to charge sealed batteries at a slower rate)

If your split charger has a manual switch or connects the batteries when the ignition is on, by using a relay for example, then you'd be best off connecting the MPPT output to the leisure battery