Check my components

Drizzt321Drizzt321 Registered Users Posts: 4
So, I'm pretty new at solar and for me electricity is mostly french for "don't mess with it". All that said, I'm planning on doing an e-bike at Burning Man, and since it's off grid and I don't fancy a generator, I thought I'd go solar to charge up the SLA pack (I've got a bike trailer to haul them around on, so weight is less of an issue). The pack runs at 36v, but in my searches any 36v solar charge controller is $$$. At least that I've found. So, I figure since I'm just buying 3 12v batteries, I'll just charge all of the batteries individually at the same time off of the same panel(s).

So here's the parts I'm thinking of using:

2x30W panels (nominal output 36v) (http://www.amazon.com/Goliath®-Solar-Module-Battery-Charging/dp/B00DVZS6GG)
3x12/24V 10A charging circuits (http://www.amazon.com/Charge-Controller-Battery-Regulator-Protection/dp/B00AE3UEUE)

Hook the 2 panels up in parallel to the 3 charge circuits, with each circuit hooked up to 1 of the batteries. Thing is, I'm not sure if I'm reading the charge controller correctly or not. If I give it the higher voltage (panels meant for 24v charging), will it automatically try and charge as if they were 24v batteries? Or will they still charge 12v batteries and just have more power available (total Watt input not exceeding the 12v charging max Watt input)? Or should I just go with higher watt rated 12v charge panels?

Comments

  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Check my components

    Without knowing more about the charger than is shown on the Amazon page, I cannot say for sure but it is generally a bad idea to connect more than one MPPT or PWM controller to a single PV array output.
    In particular, whatever type of CC you use the laws of "don't mess with it" state unquestionably that this will only work if you disconnect the three batteries from each other before you connect any of the chargers and disconnect them completely before reconnecting the battery string. If you do not do that, you will smoke the CCs and the associated wiring in a perhaps spectacular way.
    You would be better off, in terms of labor, if you just move a single charger from one battery to the next while they are still connected. But that has a definite risk of not charging the batteries evenly.

    If you are going to be connecting and disconnecting the batteries many times, be sure you have a well insulated wrench and do not drop any parts or cables during the process.
    SMA SB 3000, old BP panels.
  • Drizzt321Drizzt321 Registered Users Posts: 4
    Re: Check my components

    Yes, I was planning on having all 3 batteries disconnected from anything except the CC for it.

    Why should I only connect 1 charge controller to a PV array at a time? And if that is so, can you point me to a decently priced 36v batter charge controller? I just need it to be decent enough, and not have to handle more than 10 amps or so tops, given that I'll use 2 or 3 panels (correctly connect serial/parallel depending on CC requirements).
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Check my components
    Drizzt321 wrote: »
    Yes, I was planning on having all 3 batteries disconnected from anything except the CC for it.

    Why should I only connect 1 charge controller to a PV array at a time? And if that is so, can you point me to a decently priced 36v batter charge controller? I just need it to be decent enough, and not have to handle more than 10 amps or so tops, given that I'll use 2 or 3 panels (correctly connect serial/parallel depending on CC requirements).

    A PWM CC will be trying to adjust its duty cycle to get the required average output voltage at the battery terminals. In doing so it will pull down the panel voltage to some fixed voltage above the battery voltage that it is connected to. That in turn may force the other CCs to try to increase their duty cycle to make up, causing the first CC to readjust in turn. This process may or may not converge to a stable solution.
    An MPPT CC, on the other hand, will sweep its input voltage (by changing the current it is drawing) to try to find the combination of voltage and current that gives the most power. If another MPPT CC (or a PWM CC) is also drawing current from the panel, that process is likely to fail.
    A shunt-type CC (not used much anymore, but who knows....) will short out the panels when the battery voltage gets too high, and that will really mess up the other chargers.
    SMA SB 3000, old BP panels.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Check my components

    no matter what this will cost you far more than you may be willing to spend. it would be helpful if we knew the capacity of the batteries in amp hours, but i suspect they aren't small in their capacity. if they were 100ah batteries for example then you can draw the batteries down to 50ah without messing up the lifespan of the batteries. now you would roughly have 5hrs worth tops of 1000w/m^2 of sun to charge with so at 36v at 50a is 1800wh. it takes far more than that to charge those batteries and you would have clouds and rain at times too so you would need to double that minimally imo. 3600wh over 5hrs is 720w to the batteries and is a far cry from a 30w pv and a cheap controller. what's worse is the batteries will need to charge during the day when you are probably thinking of using it so unless you can have an extra bank of batteries charging while you use the bike then this is apt to fail miserably with the batteries prematurely dying.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Check my components
    Drizzt321 wrote: »
    can you point me to a decently priced 36v batter charge controller?

    As inetdog explained, do NOT connect more than one charger to a single array.

    I looked at the charger you linked to... not much detail about the charging parameters... I'm not sure if it will properly charge your batteries (and I don't know what type and size of batteries you are planning to use).

    Genasun makes controllers that can charge a 36 volt battery. Furthermore they make BOOST mppt controllers. That means you can use a 30 volt panel to charge a 36 volt battery. The reason this is important is that the cheapest panels (per watt) are the so-called 30 volt grid-tie panels. The genasun chargers are commonly used on 36 volt golf carts with one or two GT panels on the roof of the golf cart.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Drizzt321Drizzt321 Registered Users Posts: 4
    Re: Check my components
    inetdog wrote: »
    A PWM CC will be trying to adjust its duty cycle to get the required average output voltage at the battery terminals. In doing so it will pull down the panel voltage to some fixed voltage above the battery voltage that it is connected to. That in turn may force the other CCs to try to increase their duty cycle to make up, causing the first CC to readjust in turn. This process may or may not converge to a stable solution.
    An MPPT CC, on the other hand, will sweep its input voltage (by changing the current it is drawing) to try to find the combination of voltage and current that gives the most power. If another MPPT CC (or a PWM CC) is also drawing current from the panel, that process is likely to fail.
    A shunt-type CC (not used much anymore, but who knows....) will short out the panels when the battery voltage gets too high, and that will really mess up the other chargers.

    Ah, that makes sense. And ouch. I don't think I want to do that, I'm so glad I asked here about the idea first.

    As for the batteries, I was looking at 20-30A. And yes, I realize I may need 2 packs, one for charging and one for not. And I don't actually know how much power I would use per day, which is one of the things I'm going to make sure to test out before I head there. I'll basically spend a good 3-4 hours just riding around and measure how much power I use. Because I certainly won't be using it at full power the entire time, and I won't be constantly using it the entire time. I might be simply able to get by with a good 2-4 hours of full light in the morning as I'm sleeping in.

    All that said, I'll have to check the numbers if 3 panels & 3 CC's for each battery is cheaper, or 2-3 panels with 1 CC to charge the whole thing as a pack.

    I've found a few more in research:
    http://www.batterystuff.com/battery-chargers/promite553.html which looks promising, except for the unbalanced 3rd battery port.
    http://www.altestore.com/store/Charge-Controllers/Solar-Charge-Controllers/MPPT-Solar-Charge-Controllers/Solar-Converters-MPPT-Charge-Controllers/Solar-Converters-PT-36-5A-36V-MPPT-Charge-Controller/p1380/ which matches everything, except I'd need to supply the right voltage, and I'm not sure that the panel linked earlier is enough. It has nominal 24v output, with 36v operating. I could use 3 lower voltage panels instead to get up to the 36v nominal input.
    http://genasun.com/all-products/solar-charge-controllers/for-lead/gvb-8a-pb-solar-boost-controller/ which seems to be the one vtmaps was talking about, although for 36v it's $255! I can buy 3 panels & 3 12v CCs for that or less, and that's before buying any panels.

    Alternatively, for $300 (my this is getting expensive), I can get a 'golf cart charging' kit (http://www.amazon.com/Tektrum-Universal-Solar-Battery-Charger/dp/B009JZI7SY). Which has everything, including the 36v CC. Which has the CC from http://www.tektrumcorp.com/solar_chargers.htm (scroll down a bit). Would I have to use 3 12v panels for that like they do? Or would 2 24v panels (linked below) work as well? At a guess, the 24v panels linked wouldn't work because, if I read everything correctly, the total open circuit voltage on the panels (in series) would be ~88v, which the charge controller specifies no more than 60v open.

    Hrm...I'll have to see what the total usage is for the motor over 3-4 hours continuous use on a sample battery pack. I might just have to buy 2 (maybe 3), make sure they are fully charged at home, and use them. Likely to end up cheaper that way, honestly. Especially if I basically need to have 2 packs anyway. *sigh* It's only money, right?
  • Drizzt321Drizzt321 Registered Users Posts: 4
    Re: Check my components

    As another thought, my e-bike kit will work on 48v as well, which there seem to be a good number of reasonably priced 48v CCs such as

    http://www.altestore.com/store/Charge-Controllers/Solar-Charge-Controllers/PWM-Type-Solar-Charge-Controllers/Xantrex-Solar-Charge-Controllers-PWM/Xantrex-C40-Solar-Charge-Controller-40A-122448V/p2070/
    or
    http://www.altestore.com/store/Charge-Controllers/Solar-Charge-Controllers/PWM-Type-Solar-Charge-Controllers/Morningstar-Charge-Controllers-PWM/Morningstar-ProStar-PS-15M-48V-15A-Charge-Controller-with-Display-48V/p786/

    That first one seems reasonable. And using 2 of the 24v panels linked below in serious (88v open, 72v normal, 48v nominal) would give me ~$250 for [email protected] charging. Not amazing (~0.6a), but not nothing either. Probably still cheaper, even then, to simply buy 2, maybe 3, packs and make sure they are fully charged at home.
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