Tongue box & solar mods in progress: build thread -- advice & insults welcome

Discussion in 'Cargo Carriers / Bike Racks / Other Storage Option' started by unclemark, May 13, 2015.

  1. unclemark

    unclemark Overland Park, KS

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    Haha. I know. I'm shopping for a battery on Saturday. The shop I've browsed has Crowns and Trojans, among others. I'll get something robust. I have a local source for that, and I can talk to an expert in person. I'm blabbing about the controller here because I don't have anyone I can consult in person on that topic.
     
  2. lifespeed

    lifespeed Member

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    The undersized Sunsaver 15A controller comment was for Chipperone1 contemplating the 15A controller with a 305W panel. In your case, given the current-limiting nature of the controller even if more input power is available, the SS15 is just enough. 200W/15A=13.3V so there would not be very much of the charging regime where you would be throwing away available solar panel power. Given the price increase to move up to the TS30 and the small gains to be had with your panels available power, it makes sense to save money and go with the 15A controller.

    For many electrical devices maximum amperage ratings should be approached with caution, and not operated at 100% rated capacity to enjoy maximum life. That is not the case for solar controllers. I know I have operated my 40A controller at maximum current for an hour or more (shore power input, I only get 9A from solar) and it barely gets warm. It also puts out exactly 40A according to Trimetric, so it is obviously "in control".
     
  3. unclemark

    unclemark Overland Park, KS

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    Ah geez. Back to the drawing board on the tongue box. Not really. I'm sticking with the full size box, but getting the smaller controller.

    This is excellent. I could even mount the SunSaver someplace in the camper instead of in the box. Thanks.
     
  4. chipperone1

    chipperone1 Member

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    My thoughts are......while a larger panel, in my case 305 watts, will not see full potential under ideal conditions it will perform better under adverse conditions where it will spend 99% of its time. I've looked around and Morningstar are the best MPPT that I have found although they do cost more.

    The Morningstar website is full of info and is what has steered me thus far.

    They have a "string calculator" that may be useful..............

    http://www.morningstarcorp.com/string-calculator
     
  5. rabird

    rabird Howdy!

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  6. rabird

    rabird Howdy!

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    Which produces more, $250 of panel(s) & PWM or a $250 SS MPPT & no panel!

    In your example, if 100w is more than enough what do ya do with the extra power?
     
  7. lifespeed

    lifespeed Member

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    While looking at the SS15 specs, I read they only charge Flooded Lead Acid batteries to 14.4V (see section 7 of the spec sheet). This is not good. It was not clear this parameter is adjustable, perhaps it is with the computer interface?. I believe the TS30 can be configured to do this.

    You might want to check on the ability to adjust the charging parameters of the SS15. Perhaps this is a feature you give up at the lower price point as well as the current capability? Maybe the computer interface allows adjustment?

    You really want to charge your true deep cycle battery to 14.9V for long life and full capacity. This is a very important parameter.
     
  8. unclemark

    unclemark Overland Park, KS

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    Yep. It's another $30 for the PC connector to get in there and dial it up to the 15V max. Default setting "equalizes" at 14.9. But I guess with 15V max there is no true equalization at camp. I guess I could use the equalize setting for routine charging at camp, and actually equalize at home with a different charger as needed. Either way (whether cranking the charge to 14.9V or "equalizing" every time I charge), I'll probly need the PC connector.
     
  9. rabird

    rabird Howdy!

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    more watts also keeps you in a 'ok' efficiency (if 95% is 'ok'), under less than ideal conditions .

    efficiency is ONE reason MPPT doesn't do 30% better than PWM

    [​IMG]
     
  10. lifespeed

    lifespeed Member

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    So the price advantage of the SS15 vs TS30 diminishes slightly. The ability to do equalize at 15.5V is also nice to have. Interesting comparison. Morningstar does seem to be one of the few legit controller companies. At least they give you options.

    I could talk myself into the TS30 pretty easily if it offers 15.5V equalize as well, especially if a separate charger with equalize function had to be purchased to accomplish this setting.
     
  11. rabird

    rabird Howdy!

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    efficiency drops quickly on the low end of the curve for the tristar.

    [​IMG]
     
  12. lifespeed

    lifespeed Member

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    Efficiency of the TS30 is excellent, even at 25% of a 200W panel as shown by the plot you posted. It is better than the SS15 efficiency, which I would expect for a pricier controller using more expensive MOSFETs, inductors and capacitors.

    As always, you get what you pay for. The SS15 is adequate and far better than a no-name design, but the extra-cost option to correct the charging voltage erodes the priced advantage.

    A comment on charging to 14.9V: After charging my batteries rest at 12.9V. Charging to 14.4V will result in batteries that rest at 12.7V. Anybody who has looked at a capacity vs voltage chart will understand this is significant stored power. Charging to 14.4V only gets you about 80% of a full charge.
     
  13. rabird

    rabird Howdy!

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    the charts shows at 50 watts & 29v, 93% for both, not excellent.
     
  14. lifespeed

    lifespeed Member

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    The reason PWM does 30% efficiency of a "12V" panel better than MPPT is because it is direct-connected under those conditions and is not even switching! It's weakness (lack of switched-mode regulator) becomes a small advantage under corner-case conditions. This slight benefit is not an argument in favor of PWM as it loses under all other conditions.

    The only thing PWM has going for it is cost.
     
  15. lifespeed

    lifespeed Member

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    Switched mode power supplies cannot do 98% efficiency at 5W while also accomplishing 98% efficiency at 500W. Laws of physics. The TS30 performance is indeed excellent, and sacrificing efficiency under normal conditions in order to optimize for a fraction of rated output would be a poor design choice.

    I think you may not understand the realities of electronic design.
     
  16. vinmaker

    vinmaker Member

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    I never knew Solar was so complicated. This stuff is nuts.

    Vin.
     
  17. rabird

    rabird Howdy!

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    That is why MPPT advantage does not exit at low power.

    93% is not excellent and it can be even lower.

    Environment can also cause them to loose advantage.

    [​IMG]

    During abs or float there is no advantage.

    I'd report what my cheap A PWM charge voltage is today but even today with little light it is in float, Voc is reduced to 19v vs ~22 spec. I forgo consider MS PWM a got an $8 controller while waiting to find the right controller for me. It's temp comp maxed out @ 15v during mild winter temps, I've waiting to see what it does in 110F, I hope it does not do 14.9v as that is too much when the batt is 110F.
     
  18. lifespeed

    lifespeed Member

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    You keep referencing an unlikely operating condition at the edge of design parameters which will rarely be utilized. And yes, at the edge of the operating region 93% is doing very well. I have designed switched-mode power supplies and am intimately familiar with what efficiencies are "good". If you look at the TS30 graph you can see it changes it's circuit configuration in three power "bands" to optimize efficiency over a wide range of loads. So you look at the graph and point out that this high-power controller loses a bit of efficiency at tiny outputs it will not be used at. We are talking about a 200W system, not a 20W Harbor Freight battery trickler.

    While you obviously have some experience with solar, it is clear you don't understand the design considerations and what is "good" and "efficient" for a given set of operating parameters. I'm not sure your opinion on electrical design is backed by any formal training or design experience.

    Good day,
     
  19. lifespeed

    lifespeed Member

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    Designing your cell phone is complicated, but using it is less so. Solar can be very easy to use. Choosing the ideal configuration is more complicated. In the end most any configuration will work, but some people have a desire to choose the best bang for the buck based on the different available components.
     
  20. rabird

    rabird Howdy!

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    And the OP still has no idea of his power requirements.

    There are too many real world comparisons that show MPPT is not a wise $ choice. Excluding their limited annual use.

    Interesting to ME is not sitting in a PU watching a meter, but I do enjoy the discussions and test of no name products on rv.net

    some no name products just are costly enough for some.

    This one shows bucking from 24v to 12 cost power

    http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/28346912/srt/pa/pging/1/page/1.cfm

    one of many

    http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/28353646.cfm
     

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