48V Off grid system for down payment on 6 Acres help

SERESOLAR · February 2013

hi all, im from washington state and have been building a 48v solar system for back up only for a water pump for a down payment on raw land. i have run into some issues on the final process.

The Pump:
12Amp 230V Ac for 300ft deep well

My System:
one 100w panel
a 3000W inverter for 48V
a 30Amp 48v charger
16 82AH AGM batteries

The problem
Since i have only 82AH batteries and they are in series to a bus bar for parallel i chose 4 Gauge wire for connection, since the wire is rated at 100Ah + i didnt know if it is fine or do i do my calculations off of the over all Amp Hour i am trying to achieve( 328AH ) then use a wire capable of that???

also when thats determined what are the appropriate AMP fuses i will need and where in system should they go?

thanks to whom ever reads or helps.
-Jett

Cariboocoot · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

Welcome to the forum.

Let's look at some Watts, Amps, and Volts and see what happens.
12 Amps @ 230 VAC = 2760 Watts running, probably 2880. That's about full capacity for a 3kW inverter, which actually outputs in Volt Amps. That desperately needs to be a sine wave inverter, not an "MSW" type. And it would need a really good surge rating as that pump motor on start up could draw quite a lot more power.

That amount of Watts on 48 Volts is going to be around 60 Amps. That's about the limit for 4 AWG wire, not including start up demand and allocation for running the inverter itself plus losses. So the wire size is too small.

You say you have sixteen batteries, configured for 328 Amp hours @ 48 Volts. That means you have four parallel strings of four in series. The four parallel strings even with bus bars may prove problematic for current sharing. The 60+ Amps will be a fairly hefty 18% draw, and the start surge could be nasty.

So the battery wiring at 4 AWG is definitely too small. The larger the wire the greater the current carrying capacity and the less Voltage drop that will occur under load.

The inverter is possibly too small. Without knowing the exact specs on it and the pump it is hard to say for sure.

The battery bank is also a bit on the small side, and may have trouble delivering the current needed (especially when the pump starts) all things considered.

Cariboocoot · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

Nearly forgot: a single 100 Watt panel will do nothing for charging those batteries. As it is likely to be a "12 Volt" panel it wont even have enough Voltage, much less current.

That much battery would need about 1kW of panels & an MPPT controller minimum to recharge with.

mike95490 · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

I can warn you that my 1/2 hp pump, shows 1,000 watt load via the inverter info panel. I'm about 160' of lift, with your 300', that's a lot of water to start moving, so your surge is going to be pretty hefty, at least 5x running current.

A bit of concern about those 85ah AGM batteries, they are not float or "standby" batteries are they ? When they start dieing, (and they will with 4 parallel banks) look into replacing them with 6v deep cycle batteries, for fewer parallel wire issues.

SERESOLAR · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

Thanks
Whole system is for emergencies only not continuous use.they want a system to run there pump for power outages. and from what the pumps cycle is it would give them 1200gallons at 2.5hours of continuous use. which would about put the batteries down to 50percent . This won't be pumping water continuously. the 100w panel is ofcourse too small for whole system it is a jump start for them.

Pump max amp is 12.5 . From spec sheet
Inverter is pure sine wave 3200w continuous and a surge of 8000w

And yes about 60 amps for system draw from batteries.

But my same question why can't 4 awg work I'm not worried about voltage loss because even at three feet under load would be under .1 loss and the code states 4 gauge wire can handle 135amp Maximum amps for chassis wiring
And 60 amPs for maximum amps for power transfer.

Since each battery is 82ah and wire is rated at 135 will it not work?

And what gauge are you thinking should be on .

What amp fuses should be in system and were.

Thanks for the knowledge and help.

Cariboocoot · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

I don't know what wire chart you used for your wire sizing but mine says 4 AWG has a limit of 60 for power transmission. The more you push anything towards its limit the poorer it will perform. If you have the components wired up you can measure the current draw and Voltage at the inverter.

Fuse/breaker sizing should be at 80% of the conductors' rating, or 125% of the maximum continuous current. In this case: 60 Amps * 1.25 = 75 Amps, with wire sized accordingly (2 AWG). NEC regs would peg the breaker at 100 Amps (* 1.25 * 1.25 then round up). Usually your best guide for this is the information supplied by the inverter manufacturer. If it has a particularly long surge capacity this rating may be much higher than the expected continuous current.

The more current pushed through a conductor the higher its temperature goes and lower its capacity to carry current. No one ever regretted using larger than minimum necessary size wire so long as it can fit the connectors.

SERESOLAR · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

Thanks again and YOU got it cariboocoot

i was asking (beating around the bush ) if i use the power transfer max limit for the wire or the chasis wire max limit. thanks so i had 135amps for chasis and 60 amps for power transfer.

ok now i am going to get some 75 amp fuses but how many and were should they go in system.

and one more thing my controler that i got is a PMW controller, have there been any of problems with these? its not a mppt.

my batteries are Data safe AGM for back up systems and telcom programs i have been told they will work for what im doing.

Cariboocoot · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

Ideally with four parallel battery strings each would have a fuse on its positive terminal. The fuse for the inverter would be on the wire between the bus bar where all the batteries come together and the inverter.

There is nothing wrong with PWM type charge controllers, providing you have the right array design. They do not offer much flexibility there: your 48 Volt system needs a PV array with a Vmp of around 70. You do lose some power over the MPPT type, but the question of how much and what it is worth becomes complex. Often you can get the "odd" Voltage panels for so much less per Watt that it pays for the MPPT controller. The output from the controller will dictate its wiring and circuit protection.

AGM batteries have the ability to take higher discharge rates than flooded cells, but you may still have problems owing to the four parallel strings.

SERESOLAR · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

ok well not being rude but batteries cant go lol just spent yesturday 1200 on them 75 a piece (new) with no core couldnt beat it they have 80 more to so i might add on. but sorry for not knowing but what is VMP ? and what do you mean right PV array design i am making my own panels at 100w or so a piece.

and 75 amp fuse for each series to the bus bar (4 fuses) then one after bus bar for 75 amp to the inverter Positive.

Cariboocoot · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

Panels have two Voltage ratings: Vmp is Voltage at maximum power, Voc is Voltage open circuit. A normal "12 Volt" panel will have a Vmp of 17 to 18 and a Voc about 4 Volts higher. The Voc is relevant for purposes of not exceeding the charge controller's maximum input Voltage. The Vmp is relevant to having enough Voltage to actually charge the batteries.

Panels also have two current ratings: Imp is Amps at maximum power, Isc is Amps at short circuit. The latter is relevant for testing and sizing circuit current requirements. Imp is relevant to charging current. Panels are current sources, not Voltage sources, and so under full illumination a panel will try to produce Imp at any Voltage up to Vmp, the Voltage being held "down" according to how much load is on the panel.

Considering the large size array needed to charge that battery bank, making your own panels is a rum game. The cells sold for this purpose are factory rejects, and getting all matching (including shunt resistance) is difficult and time consuming. So is assembling panels. Expecting them to be of the same quality as commercial units is unrealistic. It is very easy to make them wrong or poorly, not easy at all to make them well. Unless your time is worth nothing you can't do it economically either.

icarus · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

You just spent $1200 on batteries and you are going to do homemade PV when you can buy PV for under $1/watt? Sorry to be snarky, but this reeks of Ready, fire, aim!

Tony

SERESOLAR · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

ok and my cells are from china manufacturer brand new at 4Watts a cell. there about $100 a panel once i am complete . and also for future purposes do i have to have series and parallel pannels to run a 48V system like batteries?

will a 12v panel put power to a battery bank of 48V or does it need to be an PV array of 48 volts to even make a charge impact on batteries?

SERESOLAR · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

icarus wrote: »

You just spent $1200 on batteries and you are going to do homemade PV when you can buy PV for under $1/watt? Sorry to be snarky, but this reeks of Ready, fire, aim!

Tony

what im making is under $1/watt and is good for me. what retailer are you going through for a $/Watt?and is it good quality send PM to me please

Cariboocoot · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

Yes, they're new - but that does not mean they aren't manufacturer's rejects.

4 Watts per cell? And you will put how many in series? What's the Voltage rating on them? Where will you locate the bypass diodes?

Got to agree with Tony; this does not sound like a plan that has been well thought-through.

icarus · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

SERESOLAR wrote: »

what im making is under $1/watt and is good for me. what retailer are you going through for a $/Watt?and is it good quality send PM to me please

Do a search, even our site host has very reasonably priced panels! I get emails everyday for panels as low as $.78/watt,, with warrantee, glass frames, all in. Why would I peice together a bunch of cells on my bench, try to seal them under something (and expect them to perform for years) when I can buy them that cheap? It doesn't make sense.

Quite frankly it is something we see quite often here, and I don't know of any that have been successfull in the long term. (home made panels!)

Tony

SERESOLAR · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

volts are .519 per cell
36 in series for 144 watts at 18 V
and because of the forward voltage(900mV @6AMPs ) i will place the blocking diode on the first string neg side of my cells ,

SERESOLAR · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

icarus wrote: »

Do a search, even our site host has very reasonably priced panels! I get emails everyday for panels as low as $.78/watt,, with warrantee, glass frames, all in. Why would I peice together a bunch of cells on my bench, try to seal them under something (and expect them to perform for years) when I can buy them that cheap? It doesn't make sense.

Quite frankly it is something we see quite often here, and I don't know of any that have been successfull in the long term. (home made panels!)

Tony

ok will do thanks. i will look at paying for my panels now. and will get back to all on how the pump functions with a test run of 1 hr from my system

BB. · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

Vmp for your panels will be around 17.5-18.0 volts per panel--Which just fine for a PWM controller charging a 12 volt battery bank.

Or you can put several in series and run them through a MPPT charge controller (especially helpful if you have a longer wire run between the array and the charge controller/battery bank).

-Bill

Photowhit · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

SERESOLAR wrote: »

....and also for future purposes do i have to have series and parallel pannels to run a 48V system like batteries? ?

OK I'm late to the party, but this shows a poor understanding of what your doing, I'd stop at this point and read more or just buy new panels. I will PM you a couple places to check. Obviously if your making the panels you can design them to what ever voltage you like and have practicly any type of configuration depending on what your panels will out put.

Since you have a PWM charge controller, you might just let us know what you have?

SERESOLAR wrote: »

will a 12v panel put power to a battery bank of 48V or does it need to be an PV array of 48 volts to even make a charge impact on batteries?

More poor understanding, might read through the FAQ's at Norther Arizona Wind and Sun.

More bad news, 12Amp 230V Ac = 2760 watts(12 x 230) but at 90% inverter efiecentcy that's 3065 watts of draw the battery bank is seeing or a 63amp draw, your 328 Ah battery bank is calculated on a discharge rate of 1/20th of it's capacity and your drawing at about 1/6th of capacity.

I don't know what the capacity of AGM's are at C6 rate, but I do know forklift batteries C6 capacity is roughly 2/3rds of it's C20 capacity or your roughly 328AH battery at a C20 rate would be roughly 220 AH battery bank if the same holds true for AGMs.

Photowhit · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

Now for some good news, just because you have a 300 foot well doesn't mean you have to pump water up 300 feet, normally your water table will be much higher than that and your lift not nearly as great.

That is if your pumping water into a tank, if your pumping to spray the back pressure will add a whole other demension to the problem.

mike95490 · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

Telecom AGM batteries are made to last maybe a dozen outages, and then they are toast. Are they new manufacture batteries, or used "pulls" ?

If you are building 12V PV (18V open circuit voltage) panels, you need 4 of them to charge a 48V battery, since that battery is 4 12V cells in series.

You need another source of power, to recharge the batteries after they have been used, as your small solar array will take weeks to recharge the battery bank.

solarvic · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

So you are doing this for another party! Sounds like your clients are going to get a very poor system. Making mistakes on your own system bad enough but not acceptable do do them on a client. You could be letting yourself into a lawsuit. :grrsolarvic:grr

SERESOLAR · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

solarvic wrote: »

So you are doing this for another party! Sounds like your clients are going to get a very poor system. Making mistakes on your own system bad enough but not acceptable do do them on a client. You could be letting yourself into a lawsuit. :grrsolarvic:grr

Thanks

What are some good battery monitor brands that have been used and worked well?

BB. · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

I am on-grid--No off grid stuff, but from my reading here:

The Trimetric has been used by many--The programing/setup is a bit difficult for some--Need to re-read the manual a couple of times.

The Xantrex has an external contact--Can be programmed to set an alarm, turn off an inverter, start a genset, etc.

The Midnite battery capacity meter is "just" a voltage monitor, but the LED that warns when the battery has not been fully recharged every few days is nice.

The Victron units also have and external contact and good reviews here.

At least some starting points.

-Bill

Photowhit · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

While I love Midnite's equipment, I would stick with one of the other meters Bill has suggested since they are shunt based units and measure the current going to and coming from the battery. The Midnite, is just voltage based as Bill has stated and would not be particularly accurate with a system in use.

If you are considering a midnite classic charge controller, they intend to release a shunt based battery module for it this year, which may be the best of the integrated system monitors in time.

gww1 · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

Any comment on the doc watson battery monitor I just bought?
gww

BB. · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

I have not used one (Doc Watson link here)--But they seem pretty nice as long as you recognize their limitations.

First, the wire is not really heavy enough to carry the sustained current that they are rated out (last I looked).

· Rugged – handles 50 A continuous and 100 A peak at 60 V
· 14 ga., super fine stranded, high temperature, silicone rubber insulated wire

In reality, for an install and forget installation--You should limit it to around 20 amperes maximum. Some charts will suggest up to 32 amps maximum.

Second, they only "count up"--They are not bidirectional meters (i.e., count up when charging, count down when discharging)... So they cannot be used as a battery monitor.

Sort of like the Kill-a-Watt meter of the DC world.

-Bill

gww1 · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

Will it basicaly be redundant to what an outback system will already tell me? Mate, charge controllers.
Thanks
gww

BB. · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

No--It will be different... The charge controller and Mate (and inverter if you have one connected) only can show what they produce/consume. The typical battery monitor installation puts the shunt in the negative battery lead (to bus/ground bus) so that it can measure the current flow into/out of the battery bank directly. And--Much of what we care about is how the battery is performing and being treated (state of charge, how much energy available, etc.).

The Doc Watson meter is uni-directional only... (as far as I know). So, you would normally install it in a uni-directional electrical circuit. Such as the output of a solar panel/array, the input to a 12 VDC lighting circuit, etc.

The battery monitor is designed to go into a bi-directional electrical circuit so that it can "totalize" the total Amps*Hour current flow in/out with respect to the battery bank.

Think of a gas tank, and you monitored the fuel level with a flow meter in the line to the tank... Fuel pumped into the tank, the "totalizer" adds fuel to the total. Flow leaves the tank to the motor, the totalizer subtracts fuel from the tank. And there are settings where you can define the battery capacity (220 AH) and it Perkert Factor, temperature, etc. so it can better estimate the battery bank state of charge.

As always, the battery vs the meter will eventually drift apart--So the meters usually include a "reset to 100% full" setting (such as >14.2 volts for 3 hours).

A Doc Watson cannot do that sort of totalization or reset to full function.

-Bill

inetdog · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

BB. wrote: »

The Doc Watson meter is uni-directional only... (as far as I know).

The description says that it has "reverse polarity protection" which only weakly suggests unidirectional. Possibly they are just talking about the separate battery voltage leads for the electronics and for the voltage part of the power measurement.

gww1 · February 2013

Re: 48V Off grid system for down payment on 6 Acres help

For use of the doc watson I can hook it between my turbines and the batteries to see what they are adding to the batteries. On a 48 volt battery bank that many charge to 62 volts and above I will probly see magic smoke. I didn't relize that 48 volt battery banks would see that type of voltage when I bought the doc watson. I guess if I want the battery monitor funtion I need to look at your links.

Do I need one?

Thanks
gww

Can't put the turbines through solar charge controllers.

48V Off grid system for down payment on 6 Acres help

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