Is it safe to hookup 4x240W 24v panels to 2x6v Trojans Battery bank using a MPPT charger

wpb1971

Goodmorning everybody,
This is Bart from West Palm Beach, Florida. I have been reading posts all weekend about how to use a MPPT charge controller to use '24v panels' on a "12V system" and I sort of understand that, but all I read was people using one or two 200+W/ 24V panels.
I have 4x240 watt panels (panel specs) and 2x6v batteries Trojan T105.
Can just 2 batteries "handle the panel load" if I use a 60A MPPT Morningstar or am I going to destroy the batteries?
The reason for thinking of going 12v (for this year) is that I already have a 2500 watt pure sine inverter and I dont have the money for 2 more batteries to get a 24v battery bank.

Let me know if this is a good idea or not.
I am in West Palm Beach Florida, full sun no shade. I intend to run some lights, fans and a small apartment size 1.6A fridge. This is an off grid system.

vcallaway

Re: Is it safe to hookup 4x240W 24v panels to 2x6v Trojans Battery bank using a MPPT cha

The morningstar is not going to overcharge the batteries. Just make sure you have a battery temp sensor connected.

wpb1971

Re: Is it safe to hookup 4x240W 24v panels to 2x6v Trojans Battery bank using a MPPT cha

vcallaway wrote: »

The morningstar is not going to overcharge the batteries. Just make sure you have a battery temp sensor connected.

OK. What do I look for on the sensor and what do I do once it reaches that mark? Or does it connect to the charger?

vcallaway

Re: Is it safe to hookup 4x240W 24v panels to 2x6v Trojans Battery bank using a MPPT cha

Connects to the charge controller: http://www.solar-electric.com/prosremtempr.html

In the product description it describes if you should have one or not.

NorthGuy

Re: Is it safe to hookup 4x240W 24v panels to 2x6v Trojans Battery bank using a MPPT cha

Your panels will produce about 70A while bulk charging in full light (at 13.5V and after derating for inefficiencies). This is 32% of batteries capacity. This is way above 10-13% that Trojan recommends. Most people wouldn't consider that safe. This has a potential to heat up the batteries, and if the ambient temperature is already high (as it may be in Florida), the heat will have an adverse effect on batteries life and may even melt them.

When bulk phase is over, controller will dial the current down. If you DoD is 50%, you're looking at about an hour of bulk charging with these high currents (20-30F temperature rise, may be more). However, if your DoD is only 20-30%, the bulk phase will be very short and you can get away with this.

You may want to decrease max bulk current setting if your controller lets you.

wpb1971

Re: Is it safe to hookup 4x240W 24v panels to 2x6v Trojans Battery bank using a MPPT cha

Is it safer then to have 4 x6v Trojans connected as a 12 v battery bank?
Or isnt there much difference in 'danger level' when compared to 2x6v Trojans.

Or I might as well go for a 24v system then, with 4x6v Trojans.. and get a 24v inverter and sell my 12v inverter?

NorthGuy wrote: »

You may want to decrease max bulk current setting if your controller lets you.[/B]

Does anyone know if a Morning star 60A mppt or a xantrex/schneider 60A Mppt have this feature?

About the battery temp sensor: it says here that the XW-MPPTA-60 has

system monitoring in stand-alone applications Battery Temperature Sensor (BTS) to provide automatically temperature-compensated battery charging

and from the manual (page 20)

Introduction
1–8
975-0400-01-01
Battery Temperature Compensation
The Battery Temperature Sensor (BTS) auto
matically adjusts the charging process
of the XW SCC. With the BTS installed, the XW SCC increases or decreases the
battery charging voltage depending on the
temperature of the
battery to optimize
the charge to the battery and to protect
it from over-charge or damage. Using the
BTS can extend battery life and improve overall charging.
The BTS plugs into the BTS jack located
inside the wiring compartment of the
XW SCC.

Is that what you meant?

Thanks sofar. Really appreciated.

NorthGuy

Re: Is it safe to hookup 4x240W 24v panels to 2x6v Trojans Battery bank using a MPPT cha

wpb1971 wrote: »

Is it safer then to have 4 x6v Trojans connected as a 12 v battery bank?
Or isnt there much difference in 'danger level' when compared to 2x6v Trojans.

If you double the number of batteries, you half the amount of current into each battery. So, if it was 32%, it'll be 16% now, which is good.

However, it is better to size everything based on your loads.

wpb1971 wrote: »

Or I might as well go for a 24v system then, with 4x6v Trojans.. and get a 24v inverter and sell my 12v inverter?

IMHO, unless there's a need for 12V loads, 24V system will be better because it is more efficient.

wpb1971 wrote: »

Does anyone know if a Morning star 60A mppt or a xantrex/schneider 60A Mppt have this feature?

XW-60 already limits its output to 60A. There's a setting to limit it further if you wish. Don't know about MS-60.

wpb1971 wrote: »

About the battery temp sensor: it says here that the XW-MPPTA-60 has and from the manual (page 20).

It says that you need to purchase BTS separately, but when I received my XW SCCs they had BTS included.

Rybren

Re: Is it safe to hookup 4x240W 24v panels to 2x6v Trojans Battery bank using a MPPT cha

2500W is a lot of inverter for a 12V battery bank. If run at full rating, it will kill off your batteries fairly quickly; plus, you'd need some pretty heavy wires and a big fuse.

bmet

Re: Is it safe to hookup 4x240W 24v panels to 2x6v Trojans Battery bank using a MPPT cha

that size inverter is usually meant to be run off a running automobile, with heavy heavy gauge cables

wpb1971

Re: Is it safe to hookup 4x240W 24v panels to 2x6v Trojans Battery bank using a MPPT cha

bmet wrote: »

that size inverter is usually meant to be run off a running automobile, with heavy heavy gauge cables

What kind of 24v inverter would you recommend for lights ceilingfans and a small fridge.


Thanks for all this input so far.

wpb1971

Re: Is it safe to hookup 4x240W 24v panels to 2x6v Trojans Battery bank using a MPPT cha

Does the xw-mppt60 come with lcd screen or do you have to buy it seperatw like the morningstar mppt 60?

NorthGuy

Re: Is it safe to hookup 4x240W 24v panels to 2x6v Trojans Battery bank using a MPPT cha

wpb1971 wrote: »

Does the xw-mppt60 come with lcd screen or do you have to buy it seperatw like the morningstar mppt 60?

It does have an LCD screen, which is very good, and you can program it some. You can buy a separate Control Panel, which I think let it to be programmed more.

wpb1971

Re: Is it safe to hookup 4x240W 24v panels to 2x6v Trojans Battery bank using a MPPT cha

Can a Morningstar TS-MPPT-45 work also with these 4x240 panels
For the TS-MPPT-45 it says Max. Solar Open Circuit Voltage: 150V DC, Thats the Voc right. I have 4x36.6v=146.4

inetdog

Re: Is it safe to hookup 4x240W 24v panels to 2x6v Trojans Battery bank using a MPPT cha

wpb1971 wrote: »

Thats the Voc right. I have 4x36.6v=146.4

In cold weather or even in early morning with a cloudless sky the Voc, which increases as the temperature drops, will go over 150V, guaranteed.
You can use a 10% increase rule of thumb unless you are in a very cold climate.

wpb1971

Re: Is it safe to hookup 4x240W 24v panels to 2x6v Trojans Battery bank using a MPPT cha

inetdog wrote: »

In cold weather or even in early morning with a cloudless sky the Voc, which increases as the temperature drops, will go over 150V, guaranteed.
You can use a 10% increase rule of thumb unless you are in a very cold climate.

Ok. Thanks I'll get a 60A MPPT controller.

Cariboocoot

Re: Is it safe to hookup 4x240W 24v panels to 2x6v Trojans Battery bank using a MPPT cha

wpb1971 wrote: »

Ok. Thanks I'll get a 60A MPPT controller.

Will not make a difference: max V in is still 150. Same amount of panels produces the same output current on any MPPT charge controller. To accommodate those four panels in series you need a MidNite Classic 200 (which has an input V max of 200).