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Haltzy
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# Posted: 17 Apr 2014 08:31pm
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1 - If my current 30A CC is running at 25-28A would upgrading to a 30A MPPT CC increase my amperage output putting above the load rating of the CC. or does it just increase efficiency.
So, if I'm tapped out at 30A is their any point on putting in a 30A MPPT?
2 - I have 6 6v batteries 3 12v banks. Should i have the CC hooked up on the same lug as the feed to the inverter? It will be coming in + on one end and coming out - on the other. Is that correct?
3 - I am going to be distributing 3 12v sources from the battery bank. Power to water pump, power to outhouse, and feed to camper battery. I was looking at a 4 gang toggle switch with fuses for this. Would this work ok? there is a 5,10,15 and 20 amp switch. Trying to stay compact as this is all outside in basically a solar generator (sealed). Also considering a panel with breakers. thoughts.
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basewindow
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# Posted: 22 Apr 2014 12:34am
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Might need some more info to answer the questions.
Sytems volatge?
Panel specs and how many?
1. I'm guessing the panels are wired in parallel? Or are you going to re-wire in series for 24v and down convert to 12v battery bank.
With an MPPT CC under certain conditions you can get more than the rated Amps from your panels, so if you are running close to the 30A this might happen.
With the smaller MPPT CC you also have to have a look at the Voc rating of the controller, which can be pretty low if you are looking at a seriers configuration.
Check out the particular MPPT CC docs or specs before you buy.
2. Your battery bank is 3 parallel strings of 12v? Again it depends on your wiring configuration as to the best way to connect the inverter.
If you are using a bus bar with equal length '-' and '+' cables then attach to them.
Otherwise to the end most '-' and '+' of the entire bank, otherwise you will be discharging your batteries unevenly.
Check out this link for battery config info.
http://www.smartgauge.co.uk/batt_con.html
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MtnDon
Member
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# Posted: 22 Apr 2014 12:46am
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There are advantages to MPPT controllers, but what is best for you depends on some variables that basewindow touched on. MPPT really starts to shine when you start connecting panels in series and encounter cloudy weather for one example of "goodness".
Placing in series will bring the panel output amperage down while raising the voltage. The MPPT controller may or may not be able to handle the voltage. To be safe you take the PV Voc and multily by 1.56. If that voltage is less than the maximum voltage of the CC, then it's a go. Otherwise = possible toast.
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MtnDon
Member
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# Posted: 22 Apr 2014 12:47am
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I see the reference to the solar electric forum got deleted. Too bad, there is a lot of super info over there.
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MtnDon
Member
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# Posted: 22 Apr 2014 12:54am
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Quoting: Haltzy 3 - I am going to be distributing 3 12v sources from the battery bank. Power to water pump, power to outhouse, and feed to camper battery. I was looking at a 4 gang toggle switch with fuses for this. Would this work ok? there is a 5,10,15 and 20 amp switch.
You want to make it possible to switch from one to another? Not sure I understand why. I would simply use a separate switch (disconnect) for each. Turn on off as wanted. Just make sure the switch can handle the amount of potential maximum current and that the switch is rated for DC use.
Feeding to the camper battery has potential issues though. If the camper battery is at lower charge and you connect it to the main group, and if the main group is receiving a charge from the CC there is a likelihood of overcharging the main group as the camper battery is brought up. I would not want to do that.
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MtnDon
Member
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# Posted: 22 Apr 2014 09:37am
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Quoting: MtnDon Placing in series will bring the panel output amperage down while raising the voltage. The MPPT controller may or may not be able to handle the voltage.
BUT I misspoke a bit..... I should have also added that the amps coming out of the MPPT controller is still likely to hit 30, maybe more, and so I think if you want to take advantage of what an MPPT can offer you would be best served with a unit that can handle more amps. Then there is also the total wattage the CC can handle that needs to be looked at. All the details of the panels and the candidates for the controller would have to be known for sensible advice to be given. Sorry, ... should have never answered when late at night and tired.
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Haltzy
Member
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# Posted: 23 Apr 2014 10:55pm
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Thanks for all the feedback.
I am currently running 4 50w and 2 100w 12v panels in parallel. The 50's are ran in parallel then 4 feeds come into a combiner box, fused and sent to the CC via 8awg wire.
I have decided to not install an additional 2 6v batteries as I do not have the panel output for 660ah. I will stick with my current battery set-up which is 4 6v 440ah.
At this time I will monitor my current system to see how it performs, when i do upgrade, it will be the CC, moving up to a 40 or 45 amp MPPT. Would you recommend running the panels in series (24V) to the CC and then from the CC to the battery bank 12v? I would like to keep the battery bank 12v since i am running a lot of 12V equipment.
I do need some advice in regards to the camper battery. At this time i am running about 20' of 12/2 wire from the battery bank to my camper. This is to maintain DC charge while we are away. Basically to keep the fridge going. Last summer it seemed to work very well. Is there a safe way to do this? Am i going to wreck my batteries? I do not want to run the inverter during this time as the length between visits could be lengthy. And having basically unlimited DC power, provides us with all the necessities we need and we never plug into an AC source.
Thanks.
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MtnDon
Member
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# Posted: 24 Apr 2014 12:22am
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Quoting: Haltzy Would you recommend running the panels in series (24V) to the CC
Hard to say if you should.... If the PV array has some distance from it to the CC, definitely Yes. We're 325 feet apart and run series connected up in the 85 - 95 VDC range. That cuts the required wire gauge down.
One other advantage is making more use of the marginal sun times. When using a nominal 12 volt panel array some clouds and high temperatures can reduce the PV voltage to the point there isn't enough voltage to charge batteries. Running series can start charging earlier, run later and perform better in cloudy weather.
I am a big proponent of 24 VDC (battery) systems. IMO, 12 VDC is fine for small systems... only a couple batteries and a couple hundred watts of panels... more or less. Several reasons...
Higher volts = fewer amperes = small gauge wires.
Better use from a good charge controller. Example; our CC can handle about 800 watts of panels on a 12 VDC battery system, but 1600 on 24 VDC.
Fewer parallel connections. More serial connections are better for the batteries long life.
I know a few people who started out as 12 VDC and within 2 to 3 years changed to 24 VDC because of poor performance results on 12 VDC.
I would think about it. We run a 24 VDC system; inverter and a couple of 24 VDC items plus we have a few 12 VDC devices we run through a 24 to 12 VDC high frequency converter. Yes, that is an extra cost, but it works. There is a very small power loss in the conversion but I don't sweat it.
But then if the present system is working and keeping you happy, why change?
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Quoting: Haltzy camper battery..... ..... to maintain DC charge while we are away. Basically to keep the fridge going.
Quoting: Haltzy Am i going to wreck my batteries?
The reasons I mentioned above are valid. It might not be too bad if the main and the camper set require roughly the same charging. Technically it is a bad idea. To add issues to the ones already mentioned, if the main and camper sets of batteries have different capacities (amp-hour rating) that makes it worse. The main batteries are 6 volt in series / parallel. Is the camper battery a 12 volt RV/Marine type. Those will be a mismatch. How much worse is hard to say.
You mention running the fridge in the camper. Propane fridge with electronic controller? How much power does it draw? I seem to recall those fridges with electronic controls use maybe an ampere which is not bad, but 24/7 that adds up. It is possible that a load like that is not placing the batteries in much jeopardy as the main set requires a daily top up to replace what is lost to self discharge. Just a thought; not a guarantee of any kind.
I used to use a small stand alone panel (25 watts) and cheap controller to maintain our RV batteries over the winter. That was no actual use, just a maintenance charge. It was even partially shaded for much of the day but did the task well enough. I have a different setup now but that is because of the tricks the upscale CC can do.
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