Solar system wiring

[upston]

Hi All,

I am a liveaboard with no shore power so I have an 8 panel array of apx2000 w and 8 double height 6volt trojan LA batteries wired in series for a 48v house bank.

I just got a new back up solar controller from the Inverter store and the instructions state the array output from the SC must be run to the batteries not the inverter.

My current setup has the SC output connected to the inverter not the batteries which are 40ft away in the bilge,

I can run a new pair of cables down to the batteries but is this really necessary, my current setup has been running fine for 2 years. I was told it was OK to hook the SC to any point in the 48volt loop ???

Please tell me what I am missing as I don't want to fry anything.

Thanks Upston

[noelex 77]

Originally Posted by upston

Please tell me what I am missing as I don't want to fry anything.

Hi Upston

You will not fry anything, but the voltage drop between the batteries and the inverter will effect the battery charging algorithm of the solar contoller when the inverter is operating. This effect will be less with your 48v system than the more typical 12v boat system.

If the controller does not have a remote temperature sensing probe the temperature compensation may also be significantly wrong.

However, the system will work and may be the best solution despite the theoretical problems. How often will the inverter be running, and what sort of loads are involved? The voltage drop is easily calculated. This will give you an indication of the differnce between the true battery voltage and the voltage the solar controller will see at the inverter terminals.

[upston]

Hi Noelex

Thanks for the quick response. The lnverter is on 24/7 and the loads are mid size fridge, TV 55 inch, washer, dishwasher and other small stuff. The batteries take 4kw to reach float on an average day.

The existing SC has 3 temp settings hot warm cold and if not on the hot setting will kick the inverter on the transition from absorb to float so I leave it on hot. Never rest the batteries so SOC by voltage is a bit of a guess. Toyed with a SOC monitor but not sure the need ??

Want to keep the batteries happy so any advice would be welcome.

Thanks Upston

[noelex 77]

Originally Posted by upston

The lnverter is on 24/7 and the loads are mid size fridge, TV 55 inch, washer, dishwasher and other small stuff. The batteries take 4kw to reach float on an average day.

I presume this is house rather than a marine system.

If you know the wire size, typical load and the length of wire run the voltage difference between the battery and inverter input is easy calculate. Calculating the voltage drop is the best way to determine the significance, and therefore the difference between conecting SC direct to the batteries compared with connecting the SC to the inverter input leads. This is especially true for a house system where the wire length can be much greater than on a boat.

I suspect, in your case, providing the wire size feeding the inverter is reasonable the differnce is small, but a calculation rather than a gut feel would be better.

Originally Posted by upston

The existing SC has 3 temp settings hot warm cold

This impies the controller has no automatic (inbuilt, or better remote) temperature sensor. As the temperature is manually selected, from a temperate sensing perspective, the controller location is unimportant. I am a little surprised that a large (4kw a day) high voltage (48v) system does not have a more advanced controller but at least this removes one potential hurdle from your proposed installation.

Originally Posted by upston

and if not on the hot setting will kick the inverter on the transition from absorb to float so I leave it on hot.

Sorry I do not understand this.

[upston]

Hi Noelex

55 ft very much floating SV in Wilmington CA. Big boat and I guess a big system for a boat.

The old SC is a Xanztrex and has has the temp probe hook up but I do not have a probe , thus the defalt setting.

The inverter kicks out from high voltage and must be reset. It is cheap chinese inverter 6000w , doubt it, and the high voltage limit is 60V. If bat temp is set to warm or cold it will shut down at the end of the absorb cycle

[noelex 77]

Originally Posted by upston

Hi Noelex

55 ft very much floating SV in Wilmington CA. Big boat and I guess a big system for a boat.

You recieve another for a 55 inch screen, on a SV

Originally Posted by upston

The inverter kicks out from high voltage and must be reset. It is cheap chinese inverter 6000w , doubt it, and the high voltage limit is 60V. If bat temp is set to warm or cold it will shut down at the end of the absorb cycle

Ah, that makes sense. I don’t like the idea of reducing the correct charging battery voltage to keep the inverter happy, but other than a new inverter there is perhaps no easy solution. 60v (equivalent to 15v in a 12v system) is a high charging voltage so staying below this figure even in cold weather is not unreasonable.

One concern is the charging voltage may be only briefly spiking to a level where the inverter is shutting down. It is important for battery health that the normal charging voltage is not too low.

[a64pilot]

For SOC you can get a good idea from specific gravity or amps the bank will accept at absorption voltage.
But why not a Smart Gauge? I don’t know if one will work at 48V though.

You say the bank takes 4KW to reach float, by chance is that 4KWH?

[john61ct]

Originally Posted by a64pilot

But why not a Smart Gauge? I don’t know if one will work at 48V though.

No, 12/24V only.

A pair of coulomb counter type SoC meter could likely be made to work at the serial midpoint, ask that of Victron wrt their 712-BMV

That could be set to only allow that cheap inverter to get powered up once V is below its HVC setpoint.

But getting a better inverter would of course be better

[upston]

Hi Thanks for the help, yes 4kwh to get to float. Inverter suggestions anyone?

[john61ct]

At decent quality, big ones are pricey.

48V will narrow your options, may want to step down to a House 12V circuit, use 12V gear much as possible, then use small/cheap inverters at point of load.

Generally, Xantrex is good but terrible CS attitude.

Magnum is the best, Vanner, Victron, MasterVolt, Sterling, Outback, ProMariner but pricey.

Samlex and Tripplite solid middle ground. I've heard Morningstar is good.

[upston]

Hi John

Thanks for the list. I will check some prices. I went AC for the kitchen/ galley TV ect so getting a nice inverter is a good investment at this stage. That said the $600 6000w pure sine wave Power Jack is still working fine. I never task it above 1600 w however .

[RaymondR]

I think the restriction on connecting the inverter to the solar controller probably applies to only the load terminal on the controller and not the battery terminals because of the very high ampage inverters draw.