Basic Connection Help!

kaipo_boy

Rank newbie here. I'm grid connected at the present time, but assembling components for a trial of a small system to gradually migrate my home off the grid. I will build several stand alone systems as funds allow, so this first system is the trial/data gathering one to get my feet wet.

I will have 3 Trina 265W panels, Voc is 38.5v each, Imp 8.66A, in series with a Midnite Solar Kid charge controller. The batteries will be 4 Interstate GC type 6v golf cart batteries in series for 24v. The inverter is a 1.5kW Cotek. I have purchased all these components except the panels, still awaiting delivery of them.

Since this will be a fairly small system to partially offset my grid power use, I can watch the battery DOD and nurse it to the 50% mark then stop using the system if I have to and go back onto the grid. Initial use will be limited to a couple fridge/freezers and lights/TV etc. But I'm considering getting an Iota Engineering 24v charger to hook up to my small 2200w Ryobi (1800w sustained) genset in case I run the batteries too much before dawn and have to charge them up and can't wait for dawn.

My question is this: If I do the above, I see at least 3 discreet hook ups to the same set of batteries; the Kid charge controller has to be hooked up in order to charge the batteries... the inverter must be hooked up with BIG cables to the batteries due to current needs; and then the Iota. How is the input to the batteries from the Kid and Iota kept discreet? and then the takeoff of charge into the Cotek I'm assuming is never kept discreet but is parallel in real time all the time? Do I have to install a disconnect switch on both the Kid and the Iota and hook them in only one at a time? If so, do I have to kill input from the PV panels first before disconnecting the Kid? Or can I keep the Kid connected and/or keep the PV connected and just run the Iota without throwing any switches? I saw someone post something about destroying a charge controller by connecting it to live PV panels without connecting to the battery bank first and had to replace the charge controller... so that would mean a PV disconnect switch upstream from its input into the Kid, so at least 3 disconnect switches or panels plus a circuit breaker on the heavy line out from the battery to the inverter.

If I am correct in the above, I guess I need recommendations for 3 disconnect switches with voltage/amp recommendation, plus a circuit breaker recommendation. My cables between the 6v batteries and from battery bank to inverter are 1/0. I would guess (haven't purchased them yet) my cables from PV panels to Kid will be near 8awg? (long run, probably 25 ft or slightly more) and from Kid to batteries will be 4awg. (short run, probalby less than 4 ft). Alternatively, is there something akin to a "battery isolator" switch (common on boats) that you guys use?

thanks,

walt (Kapolei, Hawaii; probably close to 7 hours of usable light daily, nearly year round)

verdigo

I hope you haven't bought those batteries yet. I have Interstate and they really need a lot of voltage to vet a good charge on them

Mountain Don

It is not necessary to isolate the PV charge controller and the Iota charger from one another.

If the sun is shining and you determine it would be best to run the generator and the Iota charger for a while to bulk up the charge just do it. The CC will not mind. When the generator/Iota is powered off the PV and CC will take over at whatever level the CC determines is needed, assuming the sun is shining sufficiently. We sometimes run the generator in the AM and then let the PV system finish off, if we have depleted the batteries a substantial amount.


What you saw about someone destroying a CC occured when they reconnected the PV and the CC and the batteries in the wrong order. Generally the CC must be connected to the batteries first so it can determine the battery voltage and then the PV array is connected to the CC. In normal use once the CC is connected to the batteries and then to the PV array those connections are left in the connected state.

kaipo_boy

Verdigo, I have not yet purchased the batteries as they have a limited shelf life and given the panels haven't come in yet, and I would have no way to keep them healthily charged without the system more or less put together, I figured the batteries would be the last purchase. Besides, they would be from Costco, which is 10 min away. I am sorry to hear about your experience with them, as the price at costco pretty much means that would be the prime choice. They are close to 200ah each and about $80... I know everyone loves the L16's but I cannot locate a reasonably priced source in Hawaii.

kaipo_boy

Thanks, Mountain Don. Given the size of my generator I was thinking the 40A Iota? or should I just get the 25A? Do you have any experience with the Interstates? Any hint on the type of disconnector I would install between the PV, Kid, and Iota? If I'll just leave them connected all the time and not have to mess with the disconnects other than for maintenance, do I even need to have a large disconnect? Would one of those small breakers do in each case? The first bunch look like a large box with a throw handle on one side; the second bunch are labelled 'circuit breakers and they look like a small terminal block with a small plastic switch on them, both are rated at 100A; but the first cost $50-100 each, the 2nd type are maybe $10 each. Would either one work just as well?

kaipo_boy

Mountain Don wrote: »

It is not necessary to isolate the PV charge controller and the Iota charger from one another.

If the sun is shining and you determine it would be best to run the generator and the Iota charger for a while to bulk up the charge just do it. The CC will not mind. When the generator/Iota is powered off the PV and CC will take over at whatever level the CC determines is needed, assuming the sun is shining sufficiently. We sometimes run the generator in the AM and then let the PV system finish off, if we have depleted the batteries a substantial amount.


What you saw about someone destroying a CC occured when they reconnected the PV and the CC and the batteries in the wrong order. Generally the CC must be connected to the batteries first so it can determine the battery voltage and then the PV array is connected to the CC. In normal use once the CC is connected to the batteries and then to the PV array those connections are left in the connected state.

Don, thank you for the help. Does that mean if I run the genset/Iota during the day (sun shining) that its output will over-run any input from the PV/CC and the CC will shut down/go passive? In other words, the batteries will receive no input at all from the CC while the Iota/Ryobi is running?

Mountain Don

kaipo_boy wrote: »

Thanks, Mountain Don. Given the size of my generator I was thinking the 40A Iota? or should I just get the 25A? Do you have any experience with the Interstates? Any hint on the type of disconnector I would install between the PV, Kid, and Iota? If I'll just leave them connected all the time and not have to mess with the disconnects other than for maintenance, do I even need to have a large disconnect? Would one of those small breakers do in each case? The first bunch look like a large box with a throw handle on one side; the second bunch are labelled 'circuit breakers and they look like a small terminal block with a small plastic switch on them, both are rated at 100A; but the first cost $50-100 each, the 2nd type are maybe $10 each. Would either one work just as well?

The MNEPV breakers can be used as a disconnect. We use one on the PV to CC input side and one on the CC to battery side. Makes it easy when setting up the CC. I don't have one on the Iota, FWIW.

Which Iota? Depends on the battery capacity and the ability of the generator to handle the initial rush when the Iota id plugged in. FWIW we have a Honda EU2000i and it handles the 24 volt 40 amp Iota okay.

Mountain Don

kaipo_boy wrote: »

Don, thank you for the help. Does that mean if I run the genset/Iota during the day (sun shining) that its output will over-run any input from the PV/CC and the CC will shut down/go passive? In other words, the batteries will receive no input at all from the CC while the Iota/Ryobi is running?

The batteries may be receiving charge from both the generator and the CC. If/when I do that and if sunny I let the sound of the generator guide me as to when to disconnect the generator/Iota. The CC uses a battery temperature sensor so the CC will slow down if the batteries get warm. The first few times I did a generator charge I did monitor the batteries frequently and never ran into any overheating. That's in part because of our more or less cool all the time climate. Or darn cold in winter.

Jake48

noobie here need alot to asking. would i need a fuse protector incase my battery bank fails from a high current? would i need somthing like this kind a fuse to protect the battery from catching on fire? (trust me no joke), http://www.littelfuse.com/products/fuses/industrial-power-fuses/class-l-fuses/ldc/ldc1500.aspx
if so all the battery would need a fuse or just some.
lol.

BB.

That is a very nice fuse--You will probably find it pretty expensive. But, anyway, lets back up a moment.

Fuses/circuit breakers are there to protect wiring from excessive current/overheating/fire. It is not really there to protect devices, batteries, etc.. For example, you can easily damage/over heat a 100 AH lead acid battery with just 10 amps of current--If the current is supplied for a long period of time/gasses the battery dry/etc.

So--You have "layered protection". You have a fuse/breaker per wire to protect against over current, and you use charge controllers/dump controller+loads/etc. to prevent the battery bank from being over charged/over voltaged. Some battery types (various Lithium rechargeable types, others) which are sensitive to over/under voltage may even have a per cell battery management system/disconnect.

In general, think of the battery bank as the heart of your off ground power system. It is generally the souce of very high current levels--Most other devices (charge controllers, inverters, AC battery chargers, solar arrays) have only a limited capabilities to supply excessive current.

So--Typically you will have a + and - battery bus connection (common connection point). Every + lead that leaves the battery bus terminal should have a fuse/circuit breaker that protects the wire against excessive current if there is a short.

So, using the National Electric Code (NEC), you will find tables that tell you what is "acceptable" current flow through a wire+insulation type+conduit fill+ambient temperature+copper/aluminum, etc.

For typical house wiring, as an example, you want to supply 12 amps (whether at 12 VDC or 120 VAC, it really does not matter), you should use a fuse/breaker/wiring rated for:

12 amps * 1.25 NEC derating = 15 amp branch circuit rating.

In the NEC, you will see that 15 amps means a minimum of 14 AWG copper wiring.

So, in general, we do not fuse the battery based on its capability, we base the protective device on the size of the copper wire connecting to the battery. And there are different standards.

NEC tends to be conservative:

http://lugsdirect.com/WireCurrentAmp...ble-301-16.htm

While marine wiring is a bit less (note SAE gauge is slightly smaller than American Wire Gauge AWG):

http://www.boatus.com/boattech/artic...-terminals.asp (see table 3)

There are also other design consideration... Many times in solar we use larger diameter wire because we do not want much voltage drop--Especially at lower DC voltages (i.e., a 1 volt drop at 12 VDC is a serious issue; a 4 volt drop on a 120 VAC circuit can be normal).

There specific cases were we do fuse solar panels (typically when we have 3 or more panels/strings of panels in parallel) and battery banks (when we have 3 or more parallel battery strings).

The simplest way to see how all this works together is to paper design a system for your needs. It is usually much less confusing that speaking in "General Design Rules and Requirements". Small systems a usually easier than large/complex systems to understand--And mixing the requirements for your first system design can be frustrating.

-Bill

PS: I should add that fuses have their place, but many times a circuit breaker is a better choice. No spare fuses needed, easy to turn off power for servicing, etc. Larger fuses can be very expensive, and the price of a large fuse+holder+spare+on/off switch may be the same price or more vs a circuit breaker.

kaipo_boy

Thanks guys. I went ahead and ordered the Iota 40 amp charger just now then had a brief time of guilt that I should have ordered the Powermax at around $100 less for 10 more amps... but online reviews were iffy for the Powermax, some people reported problems and others said it was fine. Guess as soon as the Iota comes in, I'll be able to get the batteries. I've gone ahead and ordered the temp sensor as well for my Kid CC; does anyone recommend getting the shunt and whizbang jr? seems a bit pricey...

kaipo_boy

Oooops; also, for you folks out there with a similar "small" system (3x 250w panels, about 220ah in batteries), how do you EQ the batteries monthly? I'm assuming your panels can't produce enough power to bubble them long enough; will running a 2kw generator into the 40A Iota be enough?

Photowhit

kaipo_boy wrote: »

Oooops; also, for you folks out there with a similar "small" system (3x 250w panels, about 220ah in batteries), how do you EQ the batteries monthly? I'm assuming your panels can't produce enough power to bubble them long enough; will running a 2kw generator into the 40A Iota be enough?

You don't need a lot of current to equalize your batteries, what you need is for the batteries to be fully charged before you start equalizing, a reasonably balance system, even a system that can only provide 5% of the battery banks' capacity can equalize a battery bank.

BB.

And 5% rate of charge would be:

220 AH * 15.0 volts equalizing * 1/0.77 panel+controller deratings * 0.05 rate of charge = 207 Watt array

Should be enough to equalize quite nicely.

-Bill

kaipo_boy

BB. wrote: »

And 5% rate of charge would be:

220 AH * 15.0 volts equalizing * 1/0.77 panel+controller deratings * 0.05 rate of charge = 207 Watt array

Should be enough to equalize quite nicely.

-Bill

My thanks, Bill.
Where does the value 15.0 volts come from? Sorry, my system will be 24v, which is 4 * 6v in series.... I think the nominal charging value is 27.2v but unsure what the EQ value would be, the Kid would probably have a default setup?

Vic

kaipo_boy wrote: »

My thanks, Bill.
.... I think the nominal charging value is 27.2v but unsure what the EQ value would be, the Kid would probably have a default setup?

If you are using 27.2 V as the Absorb voltage, believe that this is much too low ... would suggest something in the range of about 29.5 V, or so.

Would expect that you would want an EQ voltage of about 31 V. All of these voltages should be temperature compensated, by using the MidNite BTS, which is an option on the MN KID. FWIW, Vic

BB.

Sorry, missed 24 volt system... So, 2x 207 Watt = 414 Watt array.

And what type of battery do you have? Minimum charging voltage (absorb) would be something in the 29-29.5 volts like Vic says. For float (after 2-6 hours of absorb charging), 27.2 would be OK.

-Bill

Photowhit

kaipo_boy wrote: »

My thanks, Bill.
Where does the value 15.0 volts come from? Sorry, my system will be 24v, which is 4 * 6v in series.... I think the nominal charging value is 27.2v but unsure what the EQ value would be, the Kid would probably have a default setup?

You typically equalize at around 31 volts for a 24 volt system (or 15.5 for a 12 volt system). Check with your battery manufacturer for their specifications.