# Trojan L16Re-2 volt Batteries

Solar Expert Posts: 70 ✭✭
My 6 six year old Interstate 380 amphour L16 batteries need changing. I am thinking about using 6 of the 1110 amphour Trojan 2 volt batteries in series. What is the general feeling about these batteries? To go from Interstate batteries to Trojan 2 volt batteries is about \$600.00 more. I am willing to pay it if it is worth it, but need some opinions.

A new member, Andy

• Banned Posts: 17,615 ✭✭✭
Re: Trojan L16Re-2 volt Batteries

If I'm reading this right, you have three parallel banks of 2 in series 6V 380 Amp/hr batteries for a total of 1140 Amp/hrs @ 12 Volts?

Trojan batteries are excellent, and putting in "all in series" instead of "three in parallel" is always a good idea for such a large capacity bank.

Curiously, I went from Trojan batteries to Interstate and was dissatisfied with the quality of the Interstates. Thus I'm going to switch back to Trojan. :roll:
• Super Moderators, Administrators Posts: 33,281 admin
Re: Trojan L16Re-2 volt Batteries

Hi Andy!

First, regarding your current vs proposed battery bank capacity...

That is 3x the capacity of your current battery bank. Do you have enough solar panels + battery charger + backup genset to keep the bank fully charged. [Oops--My mistake--The old and new banks are about the same AH capacity]

As a starting point, we use a 5-13% rule of thumb based on the 20 Hour AH bank capacity...
• 1110 AH * 0.05 = 55.5 amps ~minimum charge rate
• 1110 AH * 0.13 = 144 amps ~maximum useful charge rate
For a solar based system, that would be:
• 55.5 amps * 14.5 volts charging * 1/0.77 system derating =1,045 watts minimum solar panels (without using genset)
• 144 amps * 14.5 volts charging * 1/0.77 system derating =2,711 watts reasonable maximum solar panels
The rough rule of thumb for battery bank sizing--3 days of no sun and 50% maximum discharge--works out to 6x daily load (for long life).
• 1,110 AH / 6 = 185 AH per day at 12 volts
• 185 AH * 12 volts = 2,220 Watt*Hours per day
The rules are just rough guidelines--So depending on your needs, you can certainly "adjust them where needed for your needs".

Once you have decided on a workable bank capacity--then look at the cells to meet your needs.

But yes, I really like large cells in a single string vs a bunch of 12 batteries all connected in parallel.

Also, as you system grows, you should be looking at your total peak power needs... Generally, running more than 1,200 watts through a 12 volt bank or 2,400 watts through a 24 volt bank means some very large currents...

You may want to look at the inverter/charge controller/etc. side of the 12/24/48 volt question too.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 70 ✭✭
Re: Trojan L16Re-2 volt Batteries

Thanks again,
andy
• Super Moderators, Administrators Posts: 33,281 admin
Re: Trojan L16Re-2 volt Batteries

Andy,

Oops--My mistake on your current battery bank size... Yes, they are about the same size.

From a basic sizing point of view--your system meets the minimum size of the rules of thumb for solar panels, and is right in there for bank capacity vs daily usage.

I am guessing that 6 years from your existing bank/vendor is a good life--So you seem to be taking pretty good care of your battery bank.

Where are you located? If you are on the coast south of San Francisco--There are lots of micro-climates that can vary the amount of sun you will receive.

On the coast, you might get 4 days of fog and 2 days of sun in the summer (or even less). Go back a mile+ in the valleys, and you can get very nice warm and sunny weather.

Using PV Watts and SFO, 1 kW of solar panels, 0.52 derating (all losses together), fixed mounting, tilted at latitude:
"Station Identification"
"City:","San_Francisco"
"State:","California"
"Lat (deg N):", 37.62
"Long (deg W):", 122.38
"Elev (m): ", 5
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 37.6"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:","12.5 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value (\$)"
1, 3.62, 54, 6.75
2, 4.59, 62, 7.75
3, 5.22, 79, 9.88
4, 6.11, 89, 11.12
5, 6.36, 95, 11.88
6, 6.47, 94, 11.75
7, 7.01, 105, 13.12
8, 6.67, 99, 12.38
9, 6.62, 95, 11.88
10, 5.41, 80, 10.00
11, 3.87, 55, 6.88
12, 3.35, 50, 6.25
"Year", 5.45, 958, 119.75

You will collect around 50 to 105 kWH per month (useful AC output of an inverter).
• 50 kWH per month / 30 days per month = 1.67 kWH per day December
• 105 kWH / 30 = 3.5 kWH per day in July
So, depending on your needs--you may wish to add more solar panels to reduce the usage of utility power or genset outside of summer months.

With your system, your bank could easily manage upwards of 2.7 kWatts total of solar panels--but, again depending on your needs, that may be overkill/too expensive.

By the way, how are you monitoring your bank capacity and ensuring it is properly charged and not drawn down too much?

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 70 ✭✭
Re: Trojan L16Re-2 volt Batteries

Bill, my cabin (off the grid) is in the mountains above Philo, Mendocino county. My residence is in Pacifica, San Mateo County. So you think the Trojan 2 volt batteries is the way to go?

Andy
• Super Moderators, Administrators Posts: 33,281 admin
Re: Trojan L16Re-2 volt Batteries

Andy,

Spent the first 30 years of my life in Pacifica... Litterly we now live just over the hills now near El Camino (sunnier weather).

I would think they are a good match for your system. And you should get good life from them.

However, I am a Grid Tied guy (and not in the solar business)--So, others here can probably give you better first hand knowledge between Trojan, Surrette, etc. than me...

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Banned Posts: 17,615 ✭✭✭
Re: Trojan L16Re-2 volt Batteries

Assuming your usage estimate is correct:

2500 Watt hours / 12 Volts = 208 Amp/hours
At 50% DOD that's 416 Amp/hr battery bank. At 25% DOD it's 832, so the 1140 Trojans should be plenty.

Consider the advantages of the 2 Volt cells: fewer connections between batteries, fewer cells to check/water, and only one current path; in and out of all in a very equal manner.

I'd be concerned about charging, as with just one 60 Amp controller you're really undercharging what you've got now. This probably shortened the life by 3-4 years. The "tall case" batteries really do want a C/10 charge rate, as they are more likely to suffer from electrolyte stratification. That means you should have two 60 Amp controllers power by about 900 Watts each in order to achieve 100+ Amps of current.

Are you sure you need 2.5 kw hours a day?
• Solar Expert Posts: 70 ✭✭
Re: Trojan L16Re-2 volt Batteries

Thanks for the reply Coot. For 6 weeks I ran the power used through a Kill a WAtt meter and the average was 2.5 Kw. I have a small swimming pool for the grandkids and an electric frig so that is where the power is being used daily. I thought I might need more panels. Would you suggest another Morningstar 60 amp or get rid of the one I have and get an 80 amp Outback MPPT Controller?
Andy
• Solar Expert Posts: 300 ✭✭✭
Re: Trojan L16Re-2 volt Batteries

The 2v Trojan batteries are also a better deal than the Rolls 12CS11PS 357ah batteries by over 60%. The calculations: 330*6/1110=1.78, 1034*1/357=2.90. In other words, even if the Trojan batteries lasted 10 years instead of 15 years with the Rolls, you would still be ahead.

It was discussed awhile back, but hasn't anybody switched over to the large Thundersky lithium batteries? It would seem to require fewer cells even than the PbA chemistry, and the Depth Of Discharge can be about twice as much, and still get two thousand or so cycles.
• Solar Expert Posts: 70 ✭✭
Re: Trojan L16Re-2 volt Batteries

Coot, I am confused about the charge current amount. Lets say the battery is fully charged. I start using 350 watts of power per hour.. Thats about 30 amps per hour used from the battery. Are you saying that 60 amps from my existing panels is not enough current to charge the battery?
• Banned Posts: 17,615 ✭✭✭
Re: Trojan L16Re-2 volt Batteries
andyrud wrote: »
Coot, I am confused about the charge current amount. Lets say the battery is fully charged. I start using 350 watts of power per hour.. Thats about 30 amps per hour used from the battery. Are you saying that 60 amps from my existing panels is not enough current to charge the battery?

It's the difference between being able to "put back the used Amp hours", which can be done over time at any charge rate exceeding the self-discharge rate, and charging at rate that will create enough "activity" in the cells to reduce the sulphation effects and stir the electrolyte. Trojan recommends a C/10 rate, which in this case is 111 Amps. That does not include deducting for power going out while charging. Net charge rate is Amps in minus Amps out, because none of us shut down our inverters while recharging the batteries. That would be silly!

In my opinion the best thing for you to do would be simply add another 60 Amp controller and panels to supply it so that the two array/controller set-ups add up to the 111+ Amps.

I just knew kids came into that power usage figure somewhere!