Electric power for the various systems I wanted on Seeker was mistakenly high on my list of things to acquire when we decided to build. I soon learned that it rightly deserves a place at the bottom of the list. The technology is constantly improving and the prices for existing technology is constantly falling. If you are patient, you will either own the best available technology or used equipment at a great value. Or as in our case become the beneficiaries of generosity from someone like Ron Buttke of Wisconsin who donated a literal ton of off-grid power equipment. So now we need to learn everything we can about nickel iron batteries, inverters, charge controllers, and sundries.
There are 57 Nickel Iron batteries. By comparison they seem to be 1.2v, 200 AH. 6 – 50 watt solar panels
From: www.homepower.com Battery Chemistry
Nickel-iron (NiFe) battery technology was introduced around 1900 by Thomas Edison, so is referred to as the “Edison cell.” These batteries were originally intended to power electric vehicles but were also used for backup power for mining and railroad operations.
In NiFe batteries, the cathode is nickel oxide hydroxide [NiO(OH)], and the anode is made of iron (Fe). The electrolyte is a solution of potassium hydroxide (KOH), a little lithium hydroxide (LiOH), and water.
When discharging, the active material of the positive plate changes from nickel oxide hydroxide to Ni(OH)2, and the negative plate changes from Fe to ferrous hydroxide [Fe(OH)2], with two electrons being released at the anode and pulled in at the cathode via the external circuit for each reaction. The electrolyte is only used as a medium for the hydroxide (OH-) ions to flow through.
The process is reversed during charging. Electrons are pulled from the nickel hydroxide electrode and driven into the ferrous hydroxide electrode. The potassium hydroxide and lithium hydroxide are not reflected in the chemical equations because the electrolyte is only a catalyst and does not participate in a chemical change with the active materials during charging or discharging. Unlike an LA battery, then, the electrolyte’s specific gravity does not indicate the battery state of charge. Instead, SOC is usually measured by voltage while the battery is at rest. The nominal battery voltage is 1.2 V per cell. Nickel-iron batteries do gas during the entire charge cycle, and must be adequately vented and routinely watered.
- Long life (10,000+ cycles)
- Robust (can be overcharged and deeply discharged)
- Freeze-resistant, even if discharged
- Large acceptable operating temperature range (approximately -20°F to 190°F)
- Best in systems with daily discharge/charge (not floating)
- High cost
- Moderate efficiency (80%)
- Need a lot of watering and venting
- High rate of self-discharge (30% per month)
Rejuvenating NiFe Batteries; Fom the www.navitron.org.uk forum.
“I used to work for Exide/Chloride Batteries in the 1960’s and we used to test NiFe batteries. Good robust and long lasting – many used for miners’ cap lamps. They can be stored for ages in a discharged state. If they have been left discharged for many years then, assuming they will recover, a bit of TLC is called for. Slow charging for a long period.
If there’s a label with the ampere hour capacity it might also give you the charging rate. It would be useful to have that information. If it’s available, I would halve the charging rate and charge them for at least twice the time. But watch out for them getting hot and take regular voltage measurements. Reduce the charge current if they start getting above “warm”. Stop charging if they continue to get hot. Should come up to about 1.4v per cell. Might be a little higher or lower dependent on the charge current.
After standing for a while after a charge, they will need a gentle discharge. Suggest a current that is the equivalent of one tenth of the ampere hour capacity (i.e. what is termed as the 10 hour rate.) This type of battery was intended for slow discharge – they don’t have the high current grunt of a lead acid battery. If the cells are going to recover, then you will have to repeat the gentle charge/discharge process a few times to restore their capacity. You can work up to higher charge/discharge currents as the cells begin to recover.
As they are old there might have been some electrolyte leakage from the top of the cells with a build up of powdery scale, also might be some on the terminals. Needs to be cleaned off carefully. If there has been leakage then it’s possible that the cells have completely dried out and that that recovery will be poor. Some types of NiFe cells could be topped up but again you have to be careful because overfilling can lead to more loss of electrolyte. We used to just add a few drops of demineralised water at a time and never let the electrolyte get too high, especially when charging as the level will rise during charging and some gas will be generated. Wear eye protection.
Reconditioning alkaline cells (either NiCd or NiFe) means cleaning them out, replacing the old electrolyte with new electrolyte, and charging the hell out of them.
Safety first! Use rubber gloves and goggles! Have a supply of vinegar on hand in case you spill electrolyte on yourself. While alkaline electrolyte is not as fierce as the sulfuric acid used in lead-acid cells, it can still burn, especially if it gets into your eyes.
Rinse the emptied cells with distilled water until they are clean. Dispose of this wash water, and any spent electrolyte, in a responsible manner. In NiCd cells, the electrolyte can contain minute amounts of cadmium, so handle it as hazardous waste. In NiFe cells, the electrolyte is easier to dispose of—just neutralize it with vinegar (or hydrochloric acid, HCl, available from any pool supply house) and you can compost it.
Mix the new electrolyte using technical grade potassium hydroxide (KOH). This is available from most chemical supply stores. Stir the KOH into distilled water in a large plastic container. I use a clean, 32 gallon, heavy duty, plastic trash can. Keep adding KOH until the specific gravity of the electrolyte is between 1.2 and 1.25. This amounts to about 1 pound of KOH to 1 gallon of distilled water. If you add too much KOH, simply bring the specific gravity down by adding more distilled water. Use a clean (never used with a lead-acid battery), temperature-compensated hydrometer to measure the specific gravity of the new electrolyte. When the KOH dissolves, it will give off heat, so add the KOH slowly (about a pound at a time), mix thoroughly (I use a hunk of clean plastic conduit to stir the mixture), and wait for everything to cool off before making the specific gravity measurement. Mix all the electrolyte you will need at the same time if possible. This assures uniformity in the electrolyte.”
KOH, Potassium Hydroxide is available from chemical supply companies for about 90 cents a pound.
Lithium Hydroxide: From Noonco.com For example 1.25 g/ml (10.4 lbs/gal) ??????? of KOH to distilled water gives the longest life, while 1.34 g/ml gives the highest output (and greatly helps the cells resist freezing in cold climates). This could be very useful for those going “off the grid.” Another popular item floating around the internet is the addition of lithium hydroxide to the electrolyte. The popular misconception is that this adds to the cells capacity. In actuality, lithium hydroxide decreases the cell’s capacity somewhat, however it has a protective effect on the cell during conditions of high temperature cycling. If you choose to use KOH and lithium, the mixture I’ve been most pleased with has been: Potassium hydroxide 1.3 g/ml, lithium hydroxide 15 g/l
The ratios of solution will look like this: KOH 1.3 grams per milliliter of distilled water and then 15 grams of lithium hydrate per liter of solution. 1.3g/ml = 10.8 lbs/gal
NiFe, the nominal is 1.2V,
For a 1.2V cell: Equalise 1.65v, Boost/Adsorb 1.55v, Float 1.45v For a 1.2V cell: Equalise 1.65v, Boost/Adsorb 1.55v, Float 1.45v
NiFe seems to be charged by applying a voltage of about 1.55V to 1.65V By charging at the high level of voltage, it does however seem that a regular check of liquid level is needed.
There seems to be a convenient upper float voltage of 1.44V By convenient I mean, the voltage where they can work for months without any visual maintenance check.
It seems that they are most happy at no more than 1C. Some recommend 1/5th C or C/5 where C is the amp storage capacity of the battery, for instance 10A, 30A or 100A It is permissible to discharge continuously at any rate up to 25% above normal, and for short periods at up to six times normal. When the normal discharge rate exceeds this value, abnormal voltage drops will occur.
Sample Power Inventory; In July we used 66 Kw / day
12v DC, 270 amps, Hydraulic pump for Autopilot 1/4 * 3240 watts
Chart Plotter 16 watts1.
Ice Maker, Ice n Easy 216 watts
Navigation Lights 1/3 * 200 watts
Total ((1/4 * 3240) + 216 + 16+ (1/3 * 200)) * 24 hours = 26.6 Kw
57 Batteries, Each 1.2v, 200 AH 20c = 57 * 1.2 * 200 *.5 *.85 = 5.8 Kw
6 – 50 watt solar panels = 300 wh * 6 hr sun = 1.8 Kw. Newer panels are typically 320 watt for $200. 8 of those with 6 hours of sun would provide. 320 * 8 * 6 =15 Kw
Typical wind generators out put 1 to 2 Kw a day.