Interstate L-16s

CobbMtMan · February 2021

I bought a new 48V battery bank in October 2015 (8x6V Interstate L-16). In 2018, while turning on our clothes dryer (6A, propane gas), the power was tripped off. I investigated and found one battery had failed. I know it's not recommended, but I replaced just that one battery with a new one. Then in January 2021, a different battery in the bank failed, again upon the start of the same clothes drier.
Here are my thoughts and observations on this:
1. the failure of the second battery does not bother me that much, it was over five years old, and even Trojan and Crown don't guarantee their batteries longer than that.
2. The first failure, after only three years, does bother me.
3. Could it be the clothes dryer. I checked the clothes dryer with my Kill A Watt device, and there is not much of a spike at start up, and it did not at any time go over 6A
4. I am a stickler for never going below an 80% discharge, okay maybe a handful of times down to the late 70s, and in any case that should not be a problem, because a more significant discharge down to even 50% would overall shorten the life of the battery, not kill it. And I water the batteries consistently.
5. Here's the most perplexing thing: in both battery failures, the voltage when read while under charge spiked to crazy voltages, upwards of 30 or 40 volts, but when not under charge read around 2-3 Volts. I suppose this might indicate an internal short.
6. I now think, despite the fact that a local solar supplier sells the Interstates, that they are not idea for off grid use.
7. I will now either replace with Trojan, or KiloVault AGM, or hopefully, if I can secure a loan, upgrade to Lithium, probably the Fortress eFlex 5.4.

Any thoughts?

BB. · February 2021

Welcome to the forum CobbMtMan,

Some basic questions...

You are using distilled water (or similar) for makeup water?
You are using a hydrometer of some sort and checking cells--Ideally, keeping the spread from low to high SG within 0.030 units or less?
How are you charging the bank (solar, genset, etc.)? How much charging current... Typically 5% for summer use/emergency backup, 10% to 13% full time off grid--To ~20-25% max (i.e., 100 AH battery bank 5/10/13/20/25 amps).
Where is the system located (roughly nearest major city for hours of s66un per day)?
Voltage measurements... I am not not quite understanding. You should be seeing around 6-7 volts (across each battery). Battery voltages should match relatively closely (something like 0.1 volts max or less from battery to battery). High voltage across cells/battery typically indicates an open cell. Voltages near zero tend to indicate shorted cell/near 1.000 SG (low SG).
Any large spread in SG (or battery to battery voltage) usually suggests equalization is needed (controlled over charging of "good cells/batteries" to bring up weaker/lower charged cells to "full charge").
Nominally, 10% to 13% rate of charge is probably best for lead acid batteries (for longest service life). Under charging/over discharging is typically what kills batteries--As well as exposing plates (not checking water often enough). Over charging can be a battery killer but does not happen often with solar power systems (proper voltage set points, etc.).
Regarding your DMM (digital multi-meter)--Make sure that the batteries are good and that it reads correctly (check car battery voltage, check 120 VAC voltage, etc.)... Have seen DMMs with weak battery(ies) read consistently, but wrong (such as measuring, made up example, each of your 8x 6 volt batteries reads "8 volts", and the bank voltage reads 38 volts--they don't add up correctly).

I don't know that there were any issues with your hardware & maintenance--But before you purchase a new battery bank, I just want to make sure that all is working well first.

-Bill

mike95490 · February 2021

A kill-a-watt meter cannot measure sub-second spikes, it only reads about every 2 seconds, so you use the regular rule of thumb:starting surge is 10x running power

i only run loads after batteries have been in absorb for an hour or so, keeping batteries full is a prime consideration, to allow space for emergencies (bad storm i want to delay going outside to start the generator)

Under stiff loads, with decent batteries, I expect the inverter to fail before a "stupid simple" FLA battery .

Saggys · February 2021

I have a similar vintage bank of Interstate L16's (January 2016) 4 x 6v and so far all is good. Mine are weekend use and a month a year for vacations. I am battery shopping and system shopping as well even though everything is working good at this time.
System is definetly aging out.

706jim · February 2021

I had two Interstate Group 27 batteries in my brand new boat. Within a year I had to replace them, they simply would not hold a charge. The next set (different brand) lasted ten years. Perhaps there is a quality control issue with Interstate?

Interstate L-16s

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