That’s right, deep cycle battery replacement! Our 12 – Trojan L16 deep cycle battery array is basically worn out! This means the batteries hold up overnight, but not a full 24 hours even. We must give them a generator based ‘booster’ charge about twice a day.
When designing your system, always budget for this replacement expense! 12 new L16s looks like it will run about $3200 plus tax, ouch. Gotta have them. More on this later…
[UPDATE: We've made some progress in reconfiguring the batteries to get some new life! See the series, Deep Cycle Batteries [1] Living in End of Life ]
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I know you are down on used forklift batteries, but you really should just buy a brand new forklift battery. These things are fifteen hundred new and yes they weigh 750lbs but once in place, they will easily run an offgrid home which is a lot easier then lifting many hundreds of tons on pallets for an eight hour shift. They will last for twenty years with minimal maintenace. Put them on a large four wheel truck dolly and roll it in.
Mike I share your view but for the average off-grid user a forklift battery poses several challenges that they may not be able to cope with. The first is weight. Admittedly L-16 are heavy but they can be handled individually. Not so easy with forklift battery. Each 2V cell is as heavy or greater and the cases are often soft polyethylene that flex. In fact one potential supplier I spoke to, told me flat out not to even consider moving individual cells because they would deform under their own weight unless confined by a steel outer shell. In other words a forklift battery needs a crane or another forklift to move it. Some off grid homes are situated in places where delivery of a unit block of 1500 – 2000 pound steel case is not feasible.
Second point about used fork lift batteries, Unlike consumers, the industrial users of forklift batteries generally tend to run them hard for a full shift and charge them properly overnight. When these reach end of life they truly are used up and the remaining plates inside are not very useful.
Marshall had poor results with used telecom batteries but sometimes they are in fact the better bet. Telecom companies tend to rotate out old batteries on a calendar basis not necesarily on the basis of how much actual use they saw.
If the battery in question spent most of the time in float mode as a standby in case of an outage they would see far less service compared to a working fork lift battery that got cycled fully each shift. A buddy worked for a large telephone company. His job was to strip out the old relay based switch board centers and install digital switching centers. All the old stuff got tossed including the Gates brand Cyclone batteries. I was the happy recipient of a dozen and used them for 10 years as the battery for my sailboat that had no charging engine on board. Several others in our yacht club had similarly good experiences with these old rejected back-up batteries. It goes without saying that your mileage may vary depending on how each batch was previously used.
In theory a battery should contain enough lead to last 10 years if ( and that is a big IF) the battery is cycled and maintained exactly in accordance with manufacturers recommendation. Very few users see 10 years. If you get 5 – 7 years you are doing more things right than wrong. I have seen battery banks junked after as little as 18 months service because of neglect or abuse. Service life is directly related to depth of discharge each cycle and most manufacturers can provide data and curves showing potential life span as a function of DoD. If you consistently go to 80% then life will be closer to 300 cycles but many also show as many as 1500 cycles if you refrain from going lower than 50% DoD. when you only go to 30% or 25% another issues comes into play. A battery which is only discharged a small amount will not accept as large a charge current as a more deeply charged battery. If this charge current is too low it does not have the strenght to reverse all of the lead sulfate. Gradually over sucessive cycles this small percentage accumulates and builds up to the point the battery is choked. Traditionally manufacturers recommended running an equalization charge periodically such as monthly. But you can’t equalize a Gel or AGM without causing possible damage. Even a flooded but sealed ‘maintenance free’ battery will suffer.
It has been my observation that battery banks that are discharged to almost 50% DoD on a regular basis and occasionally to 80% so they can accept a larger hi charge then equalized or electronically de-sulfated tend to provide more watt hours per dollar compared to very light use or heavy over use(abuse) It follows that the charging system has to be matched to the battery bank capacity. Manufacturers tell you not to exceed a charge rate of 25% of the amp hour rating but they seldom if ever mention the charge rate should be at least 10% of the amp hour rating. Solar systems tend to have enough reserve to last many days without sunlight. But that also means the maximum rate is seldom as high as the required 10% minimum needed to flush out the accumulated lead sulfate. So a monthly charge session with a genverter able to at least meet the minimum of 10% and ideally hit the 25% rate is a good thing.
BATTERY CHARGING
Not all chargers are created equal. In the RV and marine world it is now common practice to have multi stage chargers that begin as constant current but finish as constant voltage chargers.
I discovered to my dismay that even now a decade later, wind and solar charger are for the most part constant voltage only and quite often the controllers simply switch to a dump load when the battery voltage reaches the level deemed ‘full charge’ Adaptive multi stage chargers on the other hand change from full 14.2volts to a ‘float voltage of 13.8V or lower depending on battery temperature. The exact derating is 27 millivolts per degree above the reference point of 77F ambient. Failure to drop the voltage does result in ‘boiled batteries’ and loss of electrolyte.
However it has also been found that failing to maintain a float voltage for a few hours after reaching the full voltage level means some small part of the lead sulfate is not reversed. that in itself may not be a problem with solar because the sun sets and the charging stops at end of day. but what about wind and micro-hydro generation that can run 27/7 for days on end.
Solar charging and generator charging that terminates as soon as the volt meter says enough are more prone to sulfate build up than overcharging and boiling batteries.
In the RV and marrine industry wher users often have acess to grid power plug in a combination charger is often the best solution. when utility power is available, the AC power is passed through to the interior AC wiring system when the generator or utility stops the inverter kicks in and continues delivering what appears like utility power to the end user. The down side to this approach is the fact the inverter size and charger output is closely linked. A 2500 watt inverter can provide 100 – 120 Amps of charging.
Unfortunately big inverters tend to be less efficient at lower outputs of half or less so if your demand is only 800 watts for a frezer and some lights the 2500 watt inverter is very inefficient. And the idling current goes up as the output wattage capacity rises. Inverters are most efficient if loaded to around 90% of theie max capacity.
for clients with very light inverter loads but the need for massive charging I often recommend having separate individual inverters matched to each load. Ie a 500 watt inverter for fridge and a 300 watt inverter for computer (only 100 – 150 for notebooks) and one for lighting sizede to wattage of sum total of all lights. Note that while motor loads really prefer pure sine wave resistive loads like lights and coffee maker do not care of they have MSW inverters. Some battery chargers for portable tools cameras etc are finicky about [ure sine wave output. MSW inveters are really cheap and the price of sine wave inverters is coming down. Several manufacturers now offer 500 watt pure sinewave inverters at reasonable prices. Sure beats having to fork out $2000 for one big inverter when most of the time you only need a few hundred watts.
To match your charger to the battery bank you can then size it to match the capacity the battery bank will handle. Last point. north american brands quite often do not have power factor correction because US consumer laws do not require it. In Europe it is law all consumer products must have a power factor of 1.0
What it boils down to is a poor quality chargers without power factor correction will need a bigger generator to deliver the full charge compared to efficient power factor corrected chargers that can work with smaller gensets.
Some but not all US designed products are now power factor corrected because they are being marketed to Europe. Many China build products lack this level of sophistication.