Questions about solar power - Page 7 - Fiberglass RV


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Old 03-10-2014, 06:46 PM   #85
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I just had a thought........
A vehicle wrap that is actually a solar wrap.
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Old 03-11-2014, 12:41 AM   #86
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Carol, battery sulphation, which is what kills a battery, starts to pick up when the battery drops below 80% of charge. As long as you have enough solar panels to support your discharge rate, just about any PWM or MPPT charge controller should get your battery above 80%. Once you make it to float mode your battery sulphation rate drops to almost nothing regardless of what kind of controller you have.
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Old 03-11-2014, 12:52 AM   #87
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My teardrop-shaped panel stand-offs and wire viaduct are made from a pine shelf board, the viaduct cap from 1/4" plywood. I drew a teardrop shape on some graph paper, transferred it to the shelf several times, and cut the profile out with a sabre saw.

From there I had to use a belt sander to get the bottoms of the standoffs so they sat flat to the trailer roof and panel. I wrapped them in thin fiberglass mat, drilled my holes in the mounts and in the trailer roof (being very, very carefull to make sure everything lined up) and attached them to the roof using Bondo. I also used Bondo to build the little contour ramp up the sides.

From there it was sanding and painting.

Oh, I also added a layer of cloth on the inside where the mounts are as well as some structural roof supports made of 1" PVC pipe cut in half, then fiberglassed for it's entire length right-to-left in the roof ridge.

We're really hoping to have the Surfside ready for Bandon, by the way.

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Old 03-11-2014, 06:45 AM   #88
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Originally Posted by RogerDat View Post
Common problem, that long run from the tug charging system back to the trailer plug has to be some heavy wire to avoid voltage drop. Have heard of people using 8 gauge or even welding leads to overcome that problem.

Voltage delivered has to be greater than battery voltage to force any charge in, and if it's just a little greater it won't charge very rapidly.
Just to avoid a common misconception, the voltage drop on the charge line is always the difference between the two sources and has nothing to do with the size of the wire. The charge line resistance determines the size of the charging current and how long the trailer battery will take to charge. As long as there is nothing on in the trailer, the trailer battery will eventually charge.


Icharge =(Vtow - Vtrailer)/ Rcharge line



Quote:
Say battery is at 70% charge, it would still have approx. 12.3 volt charge and feeding it 13 volt is not going to push much charge in. Especially if you drawing power at the same time.

That is a question that has not been asked (at least I don't think it has) how does a charge controller deal with load while charging? In regards to the state of the battery charge. How does it handle topping off the battery charge when say 3 of the 4 amps coming from solar is being used.
Tow vehicle or solar controller, both should behave the same. With a load in parallel with the trailer battery, the trailer battery is being discharged. The charge line current is still the difference between the two sources divided by the charge line resistance. If the charging current is greater than the load current, the difference will charge the battery but at a reduced rate. If the load current is greater than the charge line current then the trailer battery will continue to discharge and it's voltage will drop. When the load was a heater in a 3 way fridge, the battery was never charged and the fridge was warm. But if the load is a motor in the fridge, it's possible it could stall. Then the overload should protect the fridge. In this case a larger charge line might increase the charge current (larger wire) enough to satisfy the demand. If not, you need to increase the size of the source be it a solar array or an alternator. Raz


Edit- one additional thought. In the case of a smart controller you really are at the mercy of the software. I would assume the programmer anticipated this scenario.
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Old 03-11-2014, 07:54 AM   #89
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Old 03-11-2014, 10:18 AM   #90
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Originally Posted by peterh View Post
Carol, battery sulphation, which is what kills a battery, starts to pick up when the battery drops below 80% of charge. As long as you have enough solar panels to support your discharge rate, just about any PWM or MPPT charge controller should get your battery above 80%. Once you make it to float mode your battery sulphation rate drops to almost nothing regardless of what kind of controller you have.
Thanks Peter for the details on how you made your thru hull fitting! You are the crafty one! Look forward to seeing the Surfside at Bandon. Are you guys bringing both trailers? - his and hers?

I am pretty careful with keeping my power demand well below the solars ability to supply but admit when off the grid for more than a few days in less that perfect sunny weather keeping the battery above 80% is a tall order. Keeping it above 50% is my target with current set up & I am able to do that. Not sure that even with a bigger panel I would be able to achieve keeping it above 80% some days in the wet heavy forested wet coast, which I know you know all about. But as panels are getting smaller with more watts and due to price drop I am considering upping my panel wattage and giving my old panel to a family member who is just starting out with solar on their RV.

I guess what I am still just a tab puzzled about is as it has been suggested here more than once the PD converter with smart charger which the trailer is running off of about 50% of the time will not give a true full battery charge resulting in some sulphating. If I went with the MPPT solar controller it is able to give a fuller charge avoiding the sulphating issue but due to camping in tree covered areas my solar is not plugged in full time or fixed to the roof - only put out as needed. So if the battery its charging off the converter 50% I am assuming that some sulphating is taking place. Will the fact its running off a MPPT controller the other 50% of the time actually do anything to mitigate that? Will it reverse the sulphating issue?

Not sure yet if I should spend the extra dollars for the MPPT controller vs spending it on a larger wattage panel due to the fact I am not planning on changing out my converter any time soon. I actually talked to Reace about possible changing the converter last week as the trailer is heading his way shortly for an update of another kind .... he talked me out of it!
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Old 03-11-2014, 12:02 PM   #91
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Originally Posted by Carol H View Post
Thanks Peter for the details on how you made your thru hull fitting! You are the crafty one! Look forward to seeing the Surfside at Bandon. Are you guys bringing both trailers? - his and hers?

I guess what I am still just a tab puzzled about is as it has been suggested here more than once the PD converter with smart charger which the trailer is running off of about 50% of the time will not give a true full battery charge resulting in some sulphating. If I went with the MPPT solar controller it is able to give a fuller charge avoiding the sulphating issue but due to camping in tree covered areas my solar is not plugged in full time or fixed to the roof - only put out as needed. So if the battery its charging off the converter 50% I am assuming that some sulphating is taking place. Will the fact its running off a MPPT controller the other 50% of the time actually do anything to mitigate that? Will it reverse the sulphating issue?
Unfortunately the sun is the key no matter what controller you have. If you aren't in a sunny spot it's like sitting in the dark to a solar panel. If you are in the sun and your panel can't push your battery to it's bulk voltage your panel is likely undersized. The mppt controller might allow your panel reach it's spec'd amperage but it won't give you any extra unless your panel is a much higher voltage.

For off grid cabins etc the simple formula for minimum watts to buy is 1 solar watt for each battery amp hour. So if you have a 100amp hr bank you need a 100 watt panel. This minimum generally ensures you'll hit the bulk voltage in one day, but is still considered a minimum.

I went from 75w to 215w. Since I did that I've never had a problem unless the sun is fully blocked by trees or some massive rv .
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Old 03-11-2014, 12:30 PM   #92
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Thanks Drew, as I mentioned I do understand the issues associated with the sun and panel sizes etc.... wondering more about the sulphating issue caused by the Power Converter and reversing it with the MPPT.
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Old 03-11-2014, 12:47 PM   #93
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Sulphating issue

so with a panel fixed on the roof, the battery will never sit for long periods discharged. In fact it will get charged every day which is the ideal conditions for storing a battery. Therefore sulphating should not be an issue because the battery is always charged. MPPT vs. PWM controller will not have an effect either way, though some have functions that periodically apply pulses to reduce sulfation.

If however you use a foldable array that you put away, you then need to make sure you keep your battery charged while in storage and leaving the battery discharged will result in sulfation which will decrease the life of your battery.
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Old 03-11-2014, 12:58 PM   #94
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MPPT waste of money for small system

More panel is MUCH cheaper then using an MPPT over a PWM controller. With a MPPT you will probably get 10 to 15% more energy out of your panel then a PWM controller. The higher numbers in marketing material refer to connecting a solar panel directly to the battery. So for a 100W panel you may get 10 W more out of the panel on average (remember most of the time the panel is giving you less then the rated output under ideal condition). That MPPT will cost you $100 more than the PWM controller, but for $100 you could easily get a 30W panel. So for the same price the extra panel will give you more power.

However if you simply must maximize the performance from the one panel you have then an MPPT can be an expensive tool for optimization.

In a larger system like >500W then then additional performance from the controller can save a lot of money in extra panels and the difference in cost between a PWM and MPPT controller becomes negligible.
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Old 03-11-2014, 01:18 PM   #95
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When it comes to battery sulphaton and MPPT, PWM, and Progressive Dynamics chargers, one really isn't better than the other at preventing it. Lead sulphate only forms while a battery is discharging, not charging. That means as long as your charger, whatever it is, is pumping electrons into your battery, the battery won't sulphate. The only exception to that rule is when your battery boils and the lead plates become exposed and dry out.

As for Progressive Dynamics converters, I think they're fine for camping use, but I don't think they're the optimal for storing a trailer and its battery. For that I use a charger that's really designed to keep stored batteries in top condition, a BatteryMinder trickle charger/desulphinator.

A BatteryMinder melds electrical circuit design with an understanding of the properties of the two types of Lead Sulphate (Lead (II) Sulphate, the "good" kind, and Lead (IV) Sulphate, the "bad" kind that "sulphates" batteries) to break up the bad lead sulphates and get keep a battery in good operating condition as long as you possibly can. Using the BatteryMinder to trickle-charge your system while you're not using it is probably the single, best way to keep a battery working over the long-haul.

One of these days I'm going to write up a layman's description of how a battery becomes sulfated in accurate, understandable layman's language that a chemist could love. I started doing that again today, but, once again, got hung up in explaining the reasons why there are two types of lead sulfate and how, why, and when they form in a battery. The explaination, very literally, tries to reduce quantum physics as it applies to Chemistry -- third year Chemistry, if you're studying for a Chemistry degree -- and make it understandable to non-Chemists. I'll make it happen someday and post it.
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Old 03-11-2014, 01:19 PM   #96
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Thanks Drew, as I mentioned I do understand the issues associated with the sun and panel sizes etc.... wondering more about the sulphating issue caused by the Power Converter and reversing it with the MPPT.
I'd have to agree with some other post, MPPT wouldn't do much more to reduce battery sulphation. You might squeeze a bit more out of your panel but likely not enough to make it superior to simply adding watts.

I use MPPT because my new panel sits at 42v. When I used it with a 17v panel I never saw any real gains. At most it allowed the panel to push it's maximum 4amps, which some might argue is worth it, but I don't think it's cost effective on such a small panel, especially if you already have a working controller.
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Old 03-11-2014, 02:05 PM   #97
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<cut>

As for Progressive Dynamics converters, I think they're fine for camping use, but I don't think they're the optimal for storing a trailer and its battery. For that I use a charger that's really designed to keep stored batteries in top condition, a BatteryMinder trickle charger/desulphinator.

<cut>

One of these days I'm going to write up a layman's description of how a battery becomes sulfated in accurate, understandable layman's language that a chemist could love. .<cut>
LOL look forward to reading the first addition!! Sure to be a best seller here if you are able to keep it in simple layman's terms!!!

Got the BatteryMinder for winter storage so I guess at this point it seems on the bases of economics I will just stick with my plan to increase my panel wattage and assuming I don't get one with to high an amp output I will keep using the solar controller I already own... now when I get my forever trailer then will be the time to upgrade everything to the best and I will read your novel for sure! who knows what the best will be in a year or two! I am still amazed at how much cheaper and smaller panels have become just over the past couple of years along with the controllers. I could purchase a pretty nice high wattage system for 2 trailers for what I paid for my first panel and controller 6 years ago
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Old 03-11-2014, 04:39 PM   #98
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Many solar controllers have an"equalize" function the operates manually or automatically maybe once a month. It over charges the battery a bit, the purpose being to remove lead sulphate crystals (I think).

My iota Dls 30 charger does not have an equalize function but my T105s are two yrs old and still have a fully charged resting voltage of 12.72 and the partially discharged resting voltage agrees with the state of charge calculation my Victron battery meter gives. So I think the battery's are still A-OK.

THe battery charger has been plugged in pretty much all the time we have been camping and once a month for 24 hrs when it's been in storage.
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