My 200W, MMPT system could not recover "full charge" in bad conditions.

[rickst29]

And so, maybe it's time to add a 3rd panel.

My 2619 (finally given a name: "The Rogue", in honer of its now-discontinued MPPT Controller) was unable to recover from a tough night during the following charging day (today). The day was pretty severely compromised by smoky conditions from the fires burning in CA. (We were in CA, along the Eastern Sierra).

The #1 factor in compromised Solar Charging was the smoke. The #2 factor was: the length of effective charging day in August, has probably declined to about 7 hours under the best of conditions (maybe 30% less than the "length" of effective Solar time available in late June and early July.)

But the real killer was my power usage. Overnight, my usual loads were perhaps roughly doubled by running an air cleaner continuously, at about 40 watts.

As usual, I ran the CPAP continuously (without humidifier; maybe another 30W - but only 15W average over the "discharge" day, because I sleep barely half the length of the non-charging portion of the mid-August days. The Compressor Fridge ran at an average of about 30% cycle time from the end of the previous charging and travel day for about the first half of the night - that's another 30 watts for half the night, followed by maybe 5 watts average until the charging day began. (I'll SWAG an average of 20 watts continuous). And "phantom loads", my home-built external fridge fan (continuous) plus evening lights, probably averaged another 5W over the night.

To summarize: my "typical loading" is up around 40W through a night which starts warm, but the continuous air cleaner usage DOUBLED that figure. 80W/12V is a bit less than 7 Amps, and run in "discharge mode" for about 14 hours consumed about 90 Amp Hours. That's basically 1/2 of my battery bank, and my mid-AM reading (12.2V) agreed with that figure (as a rough estimate, without getting into finicky details).

The unpleasant surprise, though, was failure to charge on the road - with Solar active, AND the TV connected via Bargeman. Driving through smoky sun for the "prime" early afternoon hours, the battery got home at only 12.8V, far less than I had hoped for. I plugged it into the wall, and the Converter jumped into action, and fired up it's fan. I would not have managed a second day under such conditions, with the air cleaner running. Bummer!

(Update 9/23/2015: I have designed a solution for failure to charge from the TV, http://www.trailmanorowners.com/forum/showthread.php?t=16761).

[rickst29]

... because it was all pretty obvious (with just a cursory look).:mad:

[Redtail Cruiser]

Sounds like you should maybe start bringing a small generator with you.

[BrucePerens]

Most MPPT controllers, including my Morningstar MPPT 60, are "buck" converters. That means they can reduce the voltage coming in from the panel to charge the battery (increasing the current), but they can't increase the voltage. So, if the voltage coming in from your panels is less than 16 Volts, your battery won't charge. And the optimum under-load voltage of your panels is probably only 18 volts. So, a single panel or a group of panels in parallel would need close to full sun to work.

The solution for this is to connect your panels in series, if they aren't already so. That way, there will be a higher voltage, and even dim conditions will yield enough voltage to get you some charge. Look up the maximum open-circuit voltage, multiply by the number of your panels, and make sure you do not exceed the maximum voltage specified for your controller. At an open-circuit voltage of 21.5V, my Morningstar MPPT 60 which is specified for 150V will support up to 7 panels. Of course you could also have several strings of 7 in series which are themselves connected in parallel to make up the maximum current rating of the controller.

You will get the same wattage in series that you would in parallel, except that it will work better in dim conditions. MPPT controllers use the voltage from your panel to charge a capacitor, and then they charge the battery from the capacitor. This allows them to deliver more current, and less voltage, than their input.

The MPPT 60 is way over-specified for any amount of panels I could get on a Trailmanor. But it will run reliably, and I like that it has Ethernet.

Be careful about safety! 150 VDC is about as dangerous as 115 AC.

New fixed solar systems systems are required by the electrical code to have DC GFCIs for safety. I've not yet seen an outdoor-mountable one, and thus they can't be positioned close to the panels and aren't as helpful for an RV as they could be.

[rickst29]

Hi, Bruce! (BTW, I'm posting from Mageia-5, and did some some minor fixes and enhancements for kde, gnome, and qt in the past.) My 2x100W panels are in Series, and I've still got headroom for another 55V (open circuit voltage) before hitting the 100 volt MPPT limit. Anything less than a "48 Volt" panel can be added, although a high-power panel array will be power limited to 300W total system power at the MPPT under good conditions. But under good conditions, it would be switching into PWM mode after just a few hours anyway, because the batteries would quickly become nearly full.

Tim, I have an SUV (not a pickup), and so the slightly stinky gas-powered device would need to be inside the SUV. And we're already pretty loaded down with dog crate, down-the-road air cleaner (moved into the after reaching our destination on this trip), and "paraphernalia". And the the gas can would also take up some space, even though I've got a really good one which doesn't make smells. And finally, the generator would cost more than another panel.

I think that the "sweet spot" (for cloudy or smoky conditions, or partial shade) is right around 325-350 watts of max rated power. I have a slight issue with raising the panel-weighted shell, and another 17 lbs of glass/aluminum panel wouldn't help that issue. So I just pulled the trigger on a "135 watt flexible panel" from Ebay. It will actually run slightly less, because the current will only match the current on the existing glass/aluminum panels: 5.29A Amps (rated max). Under good conditions, the "excess" gets thrown away by the MPPT (operating as a PWM controller). But my shortfall under bad conditions - smoke or clouds - should now be resolved.

[Padgett]

A good generator inverter has a gas cap that seals when not in use. Suspect all you need is one of the smaller ones like a Honda EU1000i or Westpro WH1000i. DO NOT get one of the 800W two-strokes, they are very loud. Ones I mentioned are the quietest.

For my 2720, everything (two GC2s, solar controller, disconnect panel, and 2500W generator (I need AC) fit in the vented rear storage compartment. I have never noticed any gas odor.

(picture is with battery cover removed).

[rickst29]

And you know what they say around here: "It's a dry heat, not so bad". :rolleyes:

[Padgett]

Yeah, swamp coolers work well there.

[scrubjaysnest]

We have run in to the same marginal charge conditions also. With the loss of the 120 watt that has made things worse. In our partial shade conditions series panels would make things even worse. In town for a chore day so won't be able to keep the two portables moving with sun. The Trimetric was showing 89% soc when we left the CG. Our usage is less then Ricks and I agree the sweet spot is around 300 to 350 watts; 400 watts may give better performance for the mppt CC's.
When we get home hope to be able to repair the 120 watt panel.
Move CG's tomorrow and will have more sun for the panels but the weather guessers are calling for rain this weekend.

[LoveToCamp]

Okay, electricians. Now you have me thinking, which when it comes to electricity, means I just get puzzled.

I have a 30 amp PWM solar controller that came with the TM. Max solar voltage is 28v (max array current 30 amps).

Each panel (I have one mounted, and have one in the box, ready to mount this weekend, each polycrystalline 100w) is "open current voltage" of 21.6v, map power volts (vpm) of 17.4v, and max power current (imp) of 5.75 amps. Now, I don't know how all of that relates, but that is what the specs (http://www.windynation.com/Polycrystalline-Solar-Panels/Windy-Nation-Inc/100-Watt-Polycrystalline-Photovoltaic-Solar-Panel/-/317?p=YzE9NDU=) say for the panels.

It was mentioned that you may wire in series to increase charging performance, but you have larger MPPT controllers. I believe, from the above specs, that I should not wire mine in series, but must wire in parallel. Is that correct? I don't want to fry my system, but I also want the fasted recharge I can get. I usually have good sun, but will occasionally have overcast or periodic shadowing.

Thanks for any education you may choose to give me.

[BrucePerens]

You can't use your two panels in series with your existing controller, their maximum open circuit voltage in series is about 43 volts, more than your controller is rated for.

A PWM controller is a switch that turns on and off really fast. Thus it can limit the charge current over each second - if it would be too high, it just turns it off. And on again in a short time.

MPPT controllers can do that too. But they are better at getting the maximum charge current that you can use at any particular time out of a series string of panels.

Some MPPTs also have boost converters and can actually increase voltage. That kind is good to use if you only have one panel or if your panels must be in parallel.

[rickst29]

You can't use your two panels in series with your existing controller, their maximum open circuit voltage in series is about 43 volts, more than your controller is rated for.True, it will break the Controller. And even more to the point: wiring your two panels in Series, with a PWM Controller, will buy you zero additional charging capability when running "PWM" or "Float" mode.

The Controller will generally be 'offering' your Battery bank a voltage between 13.6 and 14.4 Volts. (Although, when the batteries are really low and willing to take all of the current which the panels can dish out, your Controller will also be able to connect the panel(s) directly to the batteries, like a shunt. This is called "Bulk Mode".) Under good conditions, one panel alone (of your two panels) can already offer more than 17 volts. When "Bulk Mode" terminates (on the basis of batteries becoming 80-85% full and showing higher voltage than the "Bulk Mode Voltage limit", or the maximum "bulk mode time" being reached, or battery temperature going to high) then your controller switches to PWM mode - it offers a lower fixed voltage, and whatever current the batteries are willing to take at that Voltage.

If you run in the normal way (a short "bulk mode" period, followed by longer "PWM and "float" modes): Then panels in Series will present the controller with lots of extra voltage - which the PWM will throw away - and the same current as just one panel.

So you should wire them in parallel. In parallel, the 2-panel Array offers the same voltage as one panel by itself, but twice the current. 17 volts is already too much Voltage (for "PWM" and "Float" mode, but the maximum power into your batteries gets the current from both panels: e.g., 14.4 Volts * 11.5 Amps = 166 Watts. (Twice as much power into the batteries as you'd get from wiring them in Series, which would be no different than one Panel alone.)

Have you got the "Y" adapters which you will need to wire them a Parallel? If not, be sure to buy one unit of each "sex" ('Single Male + 2 Female' on one, 'Single Female + 2 Male' on the other).
- - - - -
And you're right - with MPPT, it's desirable to stack them in Series and raise the Voltage on the PV Array, because it reduces wiring losses and slightly extends the charging day, and MPPT does the Excess-Voltage-to-More-Current conversion internally. But PWM Controllers want to receive PV Array Voltage which is "just a little bit" higher than the maximum which the controller will want to push into the batteries: Your 17.4 Vmp is just about perfect for a "12V" battery bank.

[LoveToCamp]

rickst, no, I don't have "Y" connectors. I have one panel on the back shell, and am adding one on the front shell. Due to the distance between, and being on separate shells, I was told I can run wires from each one to the controller, and join them at the controller. Two wires into the + port, and two wires into the - port.

[tentcamper]

rickst,

Will you always be running an air filter, or were you using it because of the smoke? I would think if you are always going to be running the air filter you need to think about a generator for backup.

What i,m reading is you can not make it longer then a day and a half with the air filter and your current pannels. Even if you add another panel, what will happen when you do not have sun for a day or two?

I try to plan for 2 days with no sun.

[Padgett]

Also with the Y connector be careful to wire exacty as shown. It is possible (don't ask) to connect them so two panels are bucking each other and you get zero out.

My two 100W poly panels with MPT controller are in parallel and I normally see 21V in bright sun and 17v on a cloudy day. Is now being a guest cottage in the grotto so tomorrow I'll see what the output is in a forest canopy.

[BrucePerens]

I think that a theoretical PWM charger that could handle series panels could provide some additional charge in dim conditions. Not as good as an MPPT.

The internal resistance of the battery is unknown at any particular time until we measure it as R = E/I. We can offer the battery any voltage we want, and we don't know if the battery accepts a charge or not until we measure the current. So, we generally regulate charge by regulating the charge current, rather than the charge voltage, until the battery reaches its target voltage at which point we ramp down the current.

[BrucePerens]

It's not quite right to say that the PWM "throws away" extra voltage. The PWM will use every bit of voltage that is there, to achieve the desired charge current. It's perfectly OK for it to put 36 volts across a 12V battery for a short time, to achieve the desired current. This was indeed touted as an advantage of PWM controllers - for example in the dated Morningstar PWM brocure here (http://support.morningstarcorp.com/wp-content/uploads/2014/07/Why-PWM-Whitepaper-January2000.pdf),
they could use a higher voltage to achieve better charge acceptance than could be achieved with a simpler controller. I think they also potentially work better than linear regulation, as a high-voltage pulse can desulfate the battery.

Your battery charger shows voltage because that's easy to understand. But it doesn't indicate what is actually happening. What is actually happening is that a charge current is flowing through the battery, and the battery is increasing in voltage.

[rickst29]

PWM Mode is either "on" or "off" at any given moment - attempting to deliver the full power of the panels into the battery bank, or delivering nothing at all. But because the switching happens so fast, the average 'current' and 'voltage' over a longer time, even 1/1000 of a second, appears as both reduced current AND reduced voltage.

The AVERAGE current will be being limited by resistance of the battery bank, exactly as you describe, or the maximum capability of the PV Array, if lower. And the AVERAGE voltage will be match the rule V=I/R. While batteries are being charged in "Bulk" (and "Absorb" means the same thing), batteries and the PV array are directly connected continuously until the voltage on the direct connection rises up to an "Absorb mode setpoint" which protects the batteries from being driven by too much power - which would overheat and damage them.

In Bulk/Absorb mode (on a PWM, the Voltage of the panels is "dragged down" according to the rule. But the current does NOT increase by very much, so the power being drawn from the array - and into the battery bank - is basically cut by the ratio of V(actual charging voltage) / (V(mp) of the array.

When the batteries reach that "Absorb mode setpoint", then the Controller should switch into "PWM" mode - doing the rapid disconnect/reconnect of the array (which further reduces power and EFFECTIVE Voltage (and effective current, according to V=I*R), to protect the batteries from damage which becomes much more likely at the higher "direct connect" voltages.
- - - - -
MPPT differs from "straight" PWM by adding a big inductor into the connection for "MPPT" Mode (which improves maximum power delivery, compared to "Absorb" mode). On the PV side, it is already disconnecting and reconnecting the PV Array, so that the Array average operating Voltage stays close to V(mp) - the maximum power point. The Inductor "translates" the PV energy, from the PV-side loops and into the Battery-side loops. But, the battery-side loops are connected (more or less) directly to the batteries, running at lower Voltage. When batteries are low, the induction process takes the nearly all the power generated by the Array - at high voltage, Vmp - and turns it into higher current on the lower-voltage Battery-side loops. With more current at about the same "battery voltage", MPPT mode can deliver more power into the batteries over the same period of time. (Faster charging.)

There is still a Battery Voltage setpoint, which an MMTP controller uses to transition from MPPT mode to PWM mode (to protect the batteries from excess charging current at higher voltage). All MPPT controllers switch to PWM mode as the batteries become full, and they run "PWM Mode" the same way as PWM controllers do.

Finally, as the batteries become even more full, both kinds of controllers should switch to "Float" mode for the last stage of charging. For this "Stage", controllers also impose a maximum current value, to avoid cooking the batteries.

My own controller makes its decisions from measuring Voltages (not current). But as you say, they're always related by the rule V=I*R.

[Padgett]

Under the natural canopy I am still getting about 15.6v from the two panels, enough for a float charge.

[BrucePerens]

If you want to figure out how MPPT works, the various IC manufacturers have published data sheets on how to use their chips in an MPPT charger. These tell you everything in tremendous detail. See Linear (http://cds.linear.com/docs/en/datasheet/8490f.pdf), OnSemi (http://www.onsemi.com/pub_link/Collateral/DN06054.PDF), TI (http://www.ti.com/lit/an/snosb76c/snosb76c.pdf), and another TI (http://www.ti.com/lit/an/slva378/slva378.pdf). And those are the ones that came up on my first Google search!

Most of them use electrolytic capacitors, rather than inductors. Electrolytics will store more energy than inductors for the same size. Also, inductors can release their stored energy as a really high voltage, with ringing, which isn't really what we want.

Electrolytic capacitors have limited lifetimes, though. Over time they will develop increased series resistance and will need to be replaced. I have a meter that measures this, perhaps in a few years I'll check out my controller.

[TheSteeleFamily]

And you know what they say around here: "It's a dry heat, not so bad". :rolleyes:

So is the flame on my stove, but I ain't putting my finger in it.:new_Eyecr

[scrubjaysnest]

rickst, no, I don't have "Y" connectors. I have one panel on the back shell, and am adding one on the front shell. Due to the distance between, and being on separate shells, I was told I can run wires from each one to the controller, and join them at the controller. Two wires into the + port, and two wires into the - port.
That will work fine; install breakers in each panel. That is how I wired the roof mounted and the portables. Breakers also give you a means to shut off a panel to work on things if need be.

[scrubjaysnest]

I think that a theoretical PWM charger that could handle series panels could provide some additional charge in dim conditions. Not as good as an MPPT.

The internal resistance of the battery is unknown at any particular time until we measure it as R = E/I. We can offer the battery any voltage we want, and we don't know if the battery accepts a charge or not until we measure the current. So, we generally regulate charge by regulating the charge current, rather than the charge voltage, until the battery reaches its target voltage at which point we ramp down the current.PWM's as a general rule will not step the series voltage down to 12 volts. To my knowledge only the MPPT's will do that. Also the recommended ratio input to out voltage is 2:1.

[scrubjaysnest]

If you want to figure out how MPPT works, the various IC manufacturers have published data sheets on how to use their chips in an MPPT charger. These tell you everything in tremendous detail. See Linear (http://cds.linear.com/docs/en/datasheet/8490f.pdf), OnSemi (http://www.onsemi.com/pub_link/Collateral/DN06054.PDF), TI (http://www.ti.com/lit/an/snosb76c/snosb76c.pdf), and another TI (http://www.ti.com/lit/an/slva378/slva378.pdf). And those are the ones that came up on my first Google search!

Most of them use electrolytic capacitors, rather than inductors. Electrolytics will store more energy than inductors for the same size. Also, inductors can release their stored energy as a really high voltage, with ringing, which isn't really what we want.

Electrolytic capacitors have limited lifetimes, though. Over time they will develop increased series resistance and will need to be replaced. I have a meter that measures this, perhaps in a few years I'll check out my controller.

Accoriding to the folks over on the solar-electric forums the best MPPT's use transformers so the input is isolated from the output.

[BrucePerens]

It isn't necessary to step the series voltage down to 12 volts. You can charge the battery with any voltage higher than 16 volts and low enough that there won't be arc-over. So, a pulse at your full series voltage would do it, as long as the overall current is limited by the PWM to that specified for the battery, so that the battery temperature doesn't go too high.

Batteries are not charged by voltage. A current is forced through them to charge them, and the battery increases in voltage as it is charged.

We're used to thinking of this as voltage because it's easier for people to understand voltage, and because of our old alternator charging systems which used linear regulation.

[BrucePerens]

Accoriding to the folks over on the solar-electric forums the best MPPT's use transformers so the input is isolated from the output.

They are talking about their home power systems with grid-tie, where they are connecting to the regional power grid and isolation is important. That doesn't make sense in the context of an RV. First, you should consider what is necessary for a transformer to work. You would need to change the DC from the panel into AC. Transformers require a constantly-changing magnetic field to work, thus AC. If you are going to go to all of that effort, you might as well take the switches you'd need and use them to drive a capacitor ladder, which can produce any voltage without the use of a transformer.

Transformers are best driven by sine waves. They become lossy when driven by square waves which would be fine for a capacitor ladder. But the circuitry to make sine waves is itself lossy. So, you would not get the conversion efficiency that you get with electrolytic capacitors.

Finally, why do we need to isolate the panels from the rest of the system on an RV rather than a home grid-tie system? For safety? In the case of a short circuit in the controller, the full voltage of the panels could be put across the output. Maybe this happens with cheap controllers, good ones (like the Morningstar I'm using) have crowbar circuits, fuses, etc. to prevent this.

All of this is why we have higher efficiencies in our DC-only RV systems than the grid-tie folks can achieve. They have to make 60 Hz sine-wave AC, and they lose around 20% of the power on the way.

Land-based solar panels require a GFI for safety, but they generally run at higher series panel voltages than we can achieve in an RV. I would not mind having a GFI once someone makes an outdoor-mountable one. It should really go at the panels, rather than the controller. Otherwise, you have a long unprotected wire run with no benefit from the GFI.

[scrubjaysnest]

They are talking about their home power systems with grid-tie, where they are connecting to the regional power grid and isolation is important. That doesn't make sense in the context of an RV. First, you should consider what is necessary for a transformer to work. You would need to change the DC from the panel into AC. Transformers require a constantly-changing magnetic field to work, thus AC. If you are going to go to all of that effort, you might as well take the switches you'd need and use them to drive a capacitor ladder, which can produce any voltage without the use of a transformer.

Transformers are best driven by sine waves. They become lossy when driven by square waves which would be fine for a capacitor ladder. But the circuitry to make sine waves is itself lossy. So, you would not get the conversion efficiency that you get with electrolytic capacitors.

Finally, why do we need to isolate the panels from the rest of the system on an RV rather than a home grid-tie system? For safety? In the case of a short circuit in the controller, the full voltage of the panels could be put across the output. Maybe this happens with cheap controllers, good ones (like the Morningstar I'm using) have crowbar circuits, fuses, etc. to prevent this.

All of this is why we have higher efficiencies in our DC-only RV systems than the grid-tie folks can achieve. They have to make 60 Hz sine-wave AC, and they lose around 20% of the power on the way.

Land-based solar panels require a GFI for safety, but they generally run at higher series panel voltages than we can achieve in an RV. I would not mind having a GFI once someone makes an outdoor-mountable one. It should really go at the panels, rather than the controller. Otherwise, you have a long unprotected wire run with no benefit from the GFI.
Has nothing to do with grid tie, they are using the same mppt CC's from Moringstar, Blue Sky and Outback as the rest of us.

[LoveToCamp]

I went out for three nights last weekend, with my additional 100w panel. My wiring seems to have worked properly, as I was fully-charged by noon each day. Ran furnace in the mornings, as DW has thin blood.

Very glad I installed a second 100w panel, as it was overcast most of the time, and I know one panel would not have kept up charging my two 12v batteries.

[Padgett]

Good rule of thumb is 1W of solar for every AH of battery. I have 210 AH in 2 GC2s & 2 100W panels. This works for my needs in sunny Florida.

Can say that one 105 AH Grp 31 AGM can start and run including stops an Olds 455 all day long when an unobtanium alternator failed 100 miles into a 1200 mile run.

[BrucePerens]

Has nothing to do with grid tie, they are using the same mppt CC's from Moringstar, Blue Sky and Outback as the rest of us.

If you look at The Morningstar MPPT Technology Primer (http://www.morningstarcorp.com/wp-content/uploads/2014/02/MPPT-Technology-Primer.pdf) you will see a clear statement that all Morningstar MPPT controllers are buck converters. A buck converter doesn't use a transformer to do its work, it has an inductor or (more recently) a capacitor as its power conversion device. You can read about the older style of inductive buck converters at the Wikipedia article on Buck Conerters (https://en.wikipedia.org/wiki/Buck_converter). But these days we use switched capacitor buck converters instead because they are more efficient, cheaper, lighter, and don't have the problem of inductive heating of their cores and the mechanical buzz created by an oscillating magnetic field. You can read a simple tutorial about switched capacitor converters in this Maxim technical note (https://www.maximintegrated.com/en/app-notes/index.mvp/id/725) and an exhaustive technical paper about them in this U.C. Berkeley paper (http://www.eecs.berkeley.edu/Pubs/TechRpts/2011/EECS-2011-94.pdf).

With all due respect, I would like to see your friends show me a schematic for a modern commercial DC-input-to-DC-output MPPT controller using a transformer to do its conversion. It just would not be as efficient as another choice. Also, there seem to be very few
DC-input-to-DC-output MPPT controllers advertising any form of input-to-output isolation. So, I think your friends are not quite up to date with the state of the art of power electronics. Not their fault. Electronics has been changing quickly and much of the way we did things when I learned has been replaced.

Now, I'll show you something that might be confusing your friends. This photo (attached) is from a fellow ham who has taken a few MPPT controlers apart, see his blog at http://www.kg4cyx.net/category/solar/
There are two things that look like transformers, don't they? But they are clearly labeled as inductors. They are in a buck converter circuit.

If designed today, they'd be better with capacitors.

It's just a question of efficiency. Sure, you could use transformers for this. And anyone who learned electronics in the 1970s and hasn't kept up might reach for a transformer, given the job, because that's how we used to do things. But more recently we have very many small devices that need extremely good power efficiency, and need to be small, light, and cheap. And thus we have learned a lot about switching power regulation, including kinds that can trade voltage for current and vice versa without transformers.

[rickst29]

And so, maybe it's time to add a 3rd panel.

The unpleasant surprise, though, was failure to charge on the road - with Solar active, AND the TV connected via Bargeman. Driving through smoky sun for the "prime" early afternoon hours, the battery got home at only 12.8V, far less than I had hoped for. I plugged it into the wall, and the Converter jumped into action, and fired up it's fan. I would not have managed a second day under such conditions, with the air cleaner running. (Update 11/01/2015: I have added a component which will charge from the TV, at up to 20A: http://www.trailmanorowners.com/forum/showthread.php?t=16733).

And I've installed the 3rd panel: 135W "flex" (saving weight, because my front torsion bar adjusters are already turned to nearly maximum "lifting power" - due to weight of the two traditional panels which are already up there.) It took longer to tape the flex to the roof than it would have taken to put on another traditional panel, and some "bumps underneath" where cables are present make it look funky. And it cost a lot more per watt. But it's taped on really tight (traditional VHB), and it offers more power than my previous panels. Total rated power is now ~330W, running in Series (5.2A @ 64V).