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Hi all! I see plenty of setups where the battery isolator is tied directly to the POS terminal of the house battery. Doesn't this have the effect of sending too much voltage into the house battery when it is fully charged? Why isn't it connected to the POS on the PV side of the Charge Controller where the CC can ensure the proper voltage is sent to the battery? You'd need a diode on the PV side (of course) to prevent reverse flow through the panels.
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Ideally the isolator will have a diode in series with both the house and the vehicle battery so that they have the same voltage drop from the alternator.
And the alternator voltage regulator will be modified to compensate for that voltage drop.
It is hard to let the PV system also charge the vehicle battery without complicating the wiring significantly.
That said, there are also battery isolators which use FETs instead of diodes to allow a very very low voltage drop across the isolating element(s).
Your reference to connecting to the PV side of the CC leads me to believe that you do not understand what the CC is doing and how a battery isolator works.SunnyBoy 3000 US, 18 BP Solar 175B panels.-
Connecting to the PV side of the CC would act as voltage input from the panels, allowing the charge controller to regulate the voltage set to the batteries, just as it would do for the panels, and hence the need for the diode to prevent the alternator from causing reverse flow through the panels when it overcomes their input.
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Like this:
[ moderator note. The diagram attached is grossly incorrect and should only be used as a example of how to do things WRONG ]Last edited by joerossjr; 11-28-2016, 08:15 PM. Reason: Pic removed because it's NOT what you should be doing.Comment
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Thanks for the moderator comment Mike90250... you haven't told me why it's wrong though. That's why I made this post. Can you explain why you wouldn't want the Charge Controller handling the charging of the battery? It's nice that you pointed out that it's wrong, but I am sure I'm not the only person that's had this question. -
1) The charge controller has internal losses and needs several volts above battery voltage, to be able to charge.
2) no fuses anywhere
3) the diode is useless and will only waste a volt of the PV power
4) no Isolator, so no idea why this will solve any problem -
I keep asking if it's bad to charge with the alternator, since the alternator continues to shoot its max voltage into the house battery regardless of the SOC of the battery. I have read about newer alternators that use PWM and are ECU controlled... their output is bad all the way around, from everything I have read. They sometimes produce 15V, sometimes less than 12V.
@Mike: The diode is there to prevent the alternator from causing reverse flow through the panels when they have no output. I didn't include fuses, as I am simply trying to illustrate what I have described to inetdog. You didn't actually think I intended that as the entire diagram did you?? That's a small part of a much larger electrical schematic which I don't need help with.
What I am thinking is for an RV, a 24V alternator could be used as input where I described, and a voltage regulator used to provide the appropriate voltage to the start battery. What would be wrong with that setup? Granted, fuses and isolator would be used as appropriate.
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I see. I would NEVER connect the alternator in parallel with the panels to the input of the Solar CC.
That seems wrong in so many ways! Among other things the alternator will not provide a high enough voltage to the PV input of the CC to actually do any reliable battery charging, so why connect it at all?
Where did that diagram come from?
The instructions for a Chinese CC? Or a DIY forum?SunnyBoy 3000 US, 18 BP Solar 175B panels.Comment
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I created it to illustrate what I was asking since you were confused with how I described it. I know what a battery isolator is for, and I know what a Charge Controller is for.
You said you would never do it, but you didn't answer what happens when the batteries are fully charged and the voltage input from the alternator never changes. Won't this negatively affect your batteries? Just like NOT having a controller that does 3 stage charging? Is the alternator output regulated to the exact voltage a battery has at full charge?? In that case it would never fully charge the batteries correct? It might get REALLY close though.
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Joe - a solar controller is *expecting* the only source to be solar panels, and are designed as such. They are NOT designed for alternators, power supplies, and the like as a substitute for panels. It is not just a voltage consideration.
The short gist of that is that solar panels are current-souces, that produce a voltage, whereas most everything else, is a voltage-source that produces a current. There is a difference, and you may want to look up that subject in other threads here. Solar charge controllers are expecting the former.
NO charge controller manufacturer states that it is ok to use an alternator as an input source for their SOLAR controller to my knowledge. AFAIK, all you will accomplish is immedately voiding your warrantee if you get it to work with some other source.
This is an impractical benchtop hack. Do it right instead, and you'll save time, money, and energy in the long run. If you want something off the shelf right away, that does more than just isolation, look into a CTEK D250S DUAL combo.Last edited by PNjunction; 11-28-2016, 06:46 AM.Comment
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Thank you PN... I have some background in electronics but it's all repair work, no design. I don't understand the difference between what you've described yet (voltage source vs current source). I'm guessing it's more than an electron-flow vs hole-flow issue. I searched the forum for "Current source" and "voltage source" and could not find the explanation. Can you provide a link to a thread that explains it? I appreciate your help.
I am sure you can see that my intention here is to provide the right voltage/current to the batteries, and I just don't see normal setups providing that (from what little I know). I read that the alternator can only charge to about 85%, and I don't understand why everyone here is not up in arms at that complete waste of money! If that is just the "cost of doing business" then I'll hit the "I believe" button and stop looking for an alternator with an adjustable external regulator, and all sorts of other things I was looking in to. (heheh) I am currently researching the CTEK you linked (with SmartPass and land power charger), and I like it so far, but what is the alternative to the OTS solution? Is there a better DIY solution or something not so immediate I have time and am not in a huge hurry. I want to do it right.
Thank you, your response has been extremely helpful so far!!!
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OK FIRST, these layered comments are terrible things in a forum, no idea where the reply is. Lets' have replies not comments
Vehicles since 1998 (OBDII), have alternators controlled from the ECU, in order to get the best EPA mileage. Earlier ones started having regulators built into the alternator, and prior to that, remote regulators. I don't follow the car forums, but any issues with over-voltage would be with something failing, lights and ECU's don't take kindly to much more than 16VDC
Slapping a 24V charging system into a 12V car is going to be asking for trouble, if you try to regulate it down to 12V, If you use PWM, you waste a LOT of power and if you use MPPT, you will fry something, MPPT controllers expect to be driven from current sources they can manipulate for power, a alternator is a voltage source and will behave very differently.
Anytime someone throws up a dangerously wrong diagram, we have to flag that so we don't get blamed for some neophyte taking it as gospel they saw on the internet.
Balmer and other reputable mfg's make good electronic isolators that provide proper regualtion for house and starter batteries. Trying to cobble something together from the parts bin has a pretty good chance of failingPowerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-ListerComment
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