MEGAWATT 60-AMP INTRODUCTION

pnichols wrote:

No misunderstanding on my part. I was just razzing ya a bit to help make a point to other posters on that inexpensive, but effective (IMHO) little BatteryMINDer charger/maintainer unit. I've use one for years on the main engine starting battery with good results.

I have a couple of HF battery maintainers but I only use them when the batts are not in the rig. But even those are not needed anymore since I have the MegaWatt.

Jajajaja on THIS forum there is no ON-TOPIC. Nothing to ask permission for. Besides it's all related...

Wagons Ho........

pnichols wrote:
Thanks much for your additional off-topic comments ... I trust that Mex is not too upset with us (me -> it's my fault).

Your comments pretty much confirm what I thought regarding an optimized portable system:

- Wire the two hinged 60 watt panels in series to both pump up the voltage and cut the current in half so as reduce wire resistance losses,

- then optimze use of the higher incoming voltage by mounting an MPPT controller right at the batteries,

- and stay away from roll-up flexible panels because you need a frame for them to aim them which negates compactness ... or forget aiming them and then run the risk of people/animals/ants stepping on them if you merely lay them on the ground.

Your comments did not (that I noticed) address the age-old question of "poly or mono?".

Thanks again .... and I apologize, Mex!

My portable panels are mono crystalline. Mono has a smaller foot print, per watt. Important with portables. Mono yields 17.0V at Isc. 17 V at Isc means less voltage overhead loss versus 18V or 19V Isc. Since the overhead loss is lower, the amperage yield per watt must be higher to get the same amount of watts per panel.
Since with portable, you aim directly at the sun, shade or diffused light benefits from poly are pretty much negated. If you camp in the desert, where it's sunny almost all the time down in Quartzsite, mono gets the edge with all the sunshine, on most days, in terms of amps harvested for size of solar panel foot print. It weighs 27 pounds.

You'll spend at a minimum $90-100 for a cheap chineseium MPPT controller. The PWM on there yields 6.6 to 7 amps/hr if the battery starts being charged after 10 am in the morning and is at a 50 to 60% SOC.

I somehow doubt there is more than .6 to .7 Amp to be gained, per hour, going with an additional $100 MPPT charge controller. .7 Amps times 6 hours of charge time in the winter in Q is a net gain of 4.2 amps into your battery, per day... maybe 35 amps to 39 amps.

Winter in Q is a worst case scenario, short days and long nights. Might be better to run the generator for an hour in the AM to put 15 amps back in the battery, and let the solar do the rest, the rest of the day.

In the spring, summer and fall, the days are longer and the nights are shorter, less draw on the battery and more amps harvested per day. Probably best to run the gen just first thing in the am in the 3 or winter months, Nov- Feb. for a bit.

Thanks much for your additional off-topic comments ... I trust that Mex is not too upset with us (me -> it's my fault).

Your comments pretty much confirm what I thought regarding an optimized portable system:

- Wire the two hinged 60 watt panels in series to both pump up the voltage and cut the current in half so as reduce wire resistance losses,

- then optimze use of the higher incoming voltage by mounting an MPPT controller right at the batteries,

- and stay away from roll-up flexible panels because you need a frame for them to aim them which negates compactness ... or forget aiming them and then run the risk of people/animals/ants stepping on them if you merely lay them on the ground.

Your comments did not (that I noticed) address the age-old question of "poly or mono?".

Thanks again .... and I apologize, Mex!

pnichols wrote:
"PWM is not wire size sensitive between panels and controller. MPPT is."

Don, would you please explain your comments above in more detail.

Based on electro-physics, the less the voltage drop (due to wire resistance) along the lowest voltage wire route (in this situation between the controller's output and the batteries) the better ... for minimum energy waste. So, shouldn't one ALWAYS have the controller - regardless of controller type - next to the battery(ies) to keep wire resistance, and hence losses, low along this path?

Based on the above, the higher voltage wire route (in this situation from the panels to the controller) can stand a bit more resistance if needed so as to have the panels out a distance from the RV and controller ... but still keeping even the wire in this path as large as practical.

I'm not talking about getting by good enough on the least expense, here. I'm talking about optimization of captured energy if one can spend just a bit more for a portable solar setup. I believe that the on-the-ball folks that put roof solar systems on their RVs try to comply with what I'm saying above. Why not take into account the same considerations when putting together a small portable system - where energy capture efficiency is just as, or more, important?

Here's the basics:

With 12V system, DC, you lose volts between panel and charge controller, based on wire gauge and length of wire. Not amps. There is already surplus "headroom" voltage coming from the panel, most of them put out from 22 to 18 or 17 Volts.

Your charge controller puts out 14.4V. It's highly unlikely you'll lose 3.6 to 2.6 volts between the panel and charge controller with any reasonable length of 14 gauge 15 amp rated wire when a 120 watt panel is putting out 6.6 Isc to 6.98 amps at 17 V.

Where you are concerned about the loss is between the charge controller once the voltage is dropped to 14.4V and the battery. This is where a short fat run of wire located as close to the battery, if your Vabs is NOT adjustable, becomes a concern. If your Vabs is adjustable at the controller, it's a non issue, you can add in Vabs at 1/10V at a time to compensate for V lost due to length of wire run to batteries from controller, within reason.

If this is a concern to you, pull the charge controller off the back of the solar panel and relocate it / mount it as close to the battery as possible without being exposed to charging fumes or gasses, with a permanent run of 12 Gauge wire and ring terminals within hopefully 3 or 4 feet of the batteries. Make the long run from the solar panel to the input side of the charge controller out of the 14 gauge 5 meter cord with quick disconnects to the input side of the charge controller.

Problem solved.

No need to make a mountain out of a mole hill.

If you need more assistance, Rjfishing can consult you on the details. He's run a bare bones basic charge controller on his rig with 190 Watts for a couple of years, same identical charge controller as on the back of my Solar Blvd 120W portable folding panel system. Works like a charm for him with 2 group 27 or 29 lead acid kmart or some such DC batteries.

This is the Jist of a portable panel system... K.I.S.S. and it works just fine. 14.4V is perfect and 100% of the Vabs requirements for most all AGM battery manufacturers.

I have been able to pull down 30 to 35 amps daily in Quartzsite, first week of January, 4 days straight, aiming the portable 120W panel 4x a day at the sun, Poloma area. Aiming it correctly in the AM until 1 pm or 2 pm is what yields the most amount of amps... By then, the battery was slowing down on taking a charge, and amps were dropping off, not because of the sun, but because the battery was getting full.

21 foot travel trailer, with a few hours of TV each night thrown in to the power usage. LED lights, refrig on, CO detector on, smoke alarm on, etc, and not worrying about if I left the lights on or off. LEDS help a lot with that.

Put those portable 12 Vdc nominal panels in series
Get a Voc of say 40Vdc or there about - works for me
Reduce that I2R loss aka POWER LOSS
1/2 the current keeping the wire resistance the same obtain a very large reduction in the power loss
Watts aka power is what it's all about - a combination of Volts and Current

A properly designed Buck Conversion stage has VERY little loss

Larger wire does not hurt PWM system
It's just that it provides no gain in a fixed location RV install over smaller wire

PWM controller will output at it's set voltage, and anything over that is just not used 18v or 16v it doesn't matter, it will pass thru the incoming amps at the voltage set point 13.6~14.4 the extra higher 3~4 volts is simply not used,
So it makes no difference to PWM what in coming is as long as it is above the set point

On the other hand MPPT will take the extra voltage and covert it to extra watts aka amps, and attempt to use and covert every erg of power it can
So any voltage saved , not lost in line drop, is extra amps into the battery
In a portable system, MPPT might be a wasted expense
A long run of wire to put the panel in the sun might result in enough voltage drop that there is little to recover with the MPPT controller vs the PWM unless you go with really large wire , which adds even more expense

Hi Phil,

My apologizes to Mex for going "off topic".

Perhaps I was not clear. The controller needs to be as close to the bank as is humanly possible without being in the same compartment.

Most "12 volt" panels put out 17 volts. The maximum we need is about 14.8 for charging. You would need a whole bunch of wire to get a 2.2 (13%) volt drop. So any wire that can handle the maximum amperage is good enough. With 100 watts that will be no more than about 7 amps.

MPPT swaps volts to amps. So voltage drop is important between the panels and the controller for MPPT to work optimally.

Salvo will tell you I am wrong about the PWM statement. But I am apparently not bright enough to understand why.

I believe MPPT does grab more energy per day. Like it or not, cost is an issue, at least for me. When I did my system panels cost was $5.50 per watt. So MPPT made lots of sense. What I did wrong was to not buy a controller that I could expand only as far as panel wattage. It is frustrating to have room for 2 more panels--and no way to add them without a new bigger capacity controller.

I disagree with portable solar as it means there is little opportunity charging happening. But then, I was a rolling stone and was rarely in the same spot 2 days in a row. Opportunity charging during storage was essential for me.

Some of my other reasons are:

I wish to be able to strike camp quickly when boondocking. i.e. wash, dress, eat, go!

I want charging to start when the sun is up--and cease when it is dark.

I want no theft issues when I am not at the RV.

Storage is already an issue in most RV's. Panels are large, bulky, and fragile.

Easily stored flexible panels are a premium price and to get the maximum benefit from them some sort of frame is going to be needed so you can tilt and twirl easily. They also may deteriorate a lot faster as warranty is typically 50% of traditional panels.

"PWM is not wire size sensitive between panels and controller. MPPT is."

Don, would you please explain your comments above in more detail.

Based on electro-physics, the less the voltage drop (due to wire resistance) along the lowest voltage wire route (in this situation between the controller's output and the batteries) the better ... for minimum energy waste. So, shouldn't one ALWAYS have the controller - regardless of controller type - next to the battery(ies) to keep wire resistance, and hence losses, low along this path?

Based on the above, the higher voltage wire route (in this situation from the panels to the controller) can stand a bit more resistance if needed so as to have the panels out a distance from the RV and controller ... but still keeping even the wire in this path as large as practical.

I'm not talking about getting by good enough on the least expense, here. I'm talking about optimization of captured energy if one can spend just a bit more for a portable solar setup. I believe that the on-the-ball folks that put roof solar systems on their RVs try to comply with what I'm saying above. Why not take into account the same considerations when putting together a small portable system - where energy capture efficiency is just as, or more, important?

pnichols wrote:

NinerBikes wrote:
propane prices in The Q For pnichols.

Thanks much for the pricing info link.

I'll probably fill the P-tank here in CA and we can usually make it through the whole trip without refilling anywhere else - 18 gallon tank.

However, we're noticing that the Quartzite nights are chilly now. I hope they start warming up soon - as we do keep the propane furnace on a low setting all night long.

We're going to do other sight-seeing in AZ after Quartzite, but hope to keep the altitudes low so we don't get into freezing nights if we wind up drycamping some of the time. Maybe we'll have to use the 12 volt tank heaters on this trip!

I'll look for a 100-130 watt portable/foldable solar system at Quartzite, but won't buy unless it's a "just right" system: The two panel sections wired in series instead of parallel and an MPPT controller that can be remounted and used back at the RV close to the batteries instead up out at the panels. Still haven't decided on poly or mono ... I'll listen carefully to the hype at Quartzite on this issue ... right now I'm leaning towards mono but am a solar-amateur on this.

If you follow rjfishing's posts on pricing at the Q, I can assure you you can save significantly on buying my lightly used portable system, and then still have money left over to buy and wire what ever charge controller your little heart desires.

When you go portable, you do pay a small premium for the package and the convenience, there's no way around it. Call it a "plug and play" premium, if you will. But with that plug and play comes not having to add other time consuming solar panel electrical projects to your already impossibly long "Honey Do" list while being retired.