How to Store Your Homemade Power – Part 2

Types of Batteries

Open Vent – Flooded

Open vent batteries are the least expensive but require maintenance. Off-grid folks usually don’t mind the minimal extra work for a substantial price break. Plus the extra hands on time needed for maintenance keeps users more in touch with their system. This type of battery contains a liquid electrolyte that surrounds and submerges the plates as well as acting as a catalyst for stored electricity to flow. Open vent lead-acid batteries are about 80% efficient meaning for every 10W that goes in, 8W will come out. The rest of the electricity will be dissipated as heat.

Here is a list of the best open vent batteries that we have found:

• Trojan T-105 - 6 volt -  225 amp-hr – 61 lbs. – Typical life: 150 cycles
• Trojan L-16 - 6 volt – 420 amp-hr – 121 lbs. – Typical life: 500 cycles
• Hawker Industrial - 12 volt – 632 thru 1690 amp-hr – 498 thru 1260 lbs. – Typical life: 2100 cycles

If you’re not sure what some of these numbers mean, don’t worry, I will explain below.

Maintenance

• 

  Hawker Industrial Batteries

  Open vent batteries have caps on top that unscrew or pop off to reveal the lead plates and an acid/water mixture called electrolyte inside, this needs to be checked every month to verify adequate water. The electrolyte should be filled to about 1 inch above the plates. If it is low, add distilled water only.

• Equalization significantly increases the life of the batteries. The boiling causes the batteries to off-gas so it is wise to check the water after you equalize. Equalization can typically be enabled through the charge controller or inverter, the user’s guide for these devices will explain how to do this.

• Heat is the enemy of batteries. Keep batteries in a cool, vented and dry environment or risk staggering inefficiency and potential damage. If you are storing batteries or simply not using them, they should have a trickle charge (solar panel) or they need to be checked on periodically. Hot environments above 80°F will significantly increase the discharge rate. When putting stored batteries back into service, be sure they have a full charge and equalize them.

• Battery voltage is given as a nominal number such as 6V or 12V, however a voltage meter hooked to a fully charged (100%) 12V battery will read 12.75V. A battery with half (50%) its total energy will read 12.14V.  Your job is to keep your batteries charged and keep sulfation under control.

VRLA (Valve Regulated Lead Acid) – Sealed Batteries

Deka AGM Battery

For situations when maintenance is a problem, sealed batteries are the solution. With no vent caps for water to escape and an immobilized electrolyte, periodic inspection is not necessary. This also means that the batteries can be stored, transported and installed in any position with minimal self discharge. The plates inside are tightly packed resulting in greater energy density as well as better vibration tolerance and shock resistance. The gasses created when charging these batteries recombine internally to replenish the electrolyte. They have pressure regulated valves that will open to let gas escape if pressure builds up to the level set by the battery manufacturer. However it is very important to prevent his from happening as there is no way to replenish the fluid that is lost. So what would cause the vents to open? Overcharge, as is done when equalizing. VRLA batteries are not to be equalized like their open-vent counterparts, it will do more harm than good and shorten the life of your batteries. However, not being able to equalize means that sealed batteries are less forgiving if they become sulfated. So pay special attention to the state of charge of these batteries to ensure they don’t fall below 12.14V, which, as stated earlier, will cause aggressive sulfation build up.

There are two main designs of VRLA batteries:

• Concord AGM 

  Absorbed Glass Mat (AGM) – This design utilizes a fibrous glass mat that serves as a separator in between the cells inside the battery. The glass mat absorbs the liquid electrolyte, suspending it between the plates and acts as a catalyst for the electro-chemical reaction to take place. Room is left for oxygen to exist within the glass mat which allows for it to recombine with the hydrogen to replenish the electrolyte.

• Gelled Electrolyte – Gel batteries are similar to flooded lead-acid batteries except for an extra ingredient, silica fume, that turns the electrolyte into a gel. This allows them to withstand wider temperature extremes and deeper discharges. A non-porous, insulating plate, such as plastic, is used between the lead plates to prevent short-circuiting. This type of sealed battery is particularly sensitive to overcharge.

Here is a list of the best VRLA batteries that we have found:

• MK Gel - 12V – 32Ah thru 225Ah – 24 thru 161 lbs. – $113 thru $744 – Typical life: 750 cycles
• Concorde AGM - 6V or 12 V – 33Ah thru 305 Ah – 23 thru 158 lbs – $127 thru $635 – Typical life:

Battery Safety – Electrical and Explosion Hazards

Safety Gear

Deep cycle batteries are one of those things that you seriously need to be careful with. Most importantly, use insulated tools when working on batteries. These are tools with handles made of plastic or that have an insulating coating such as rubber on them. Also very important is not to smoke or have any sort of open flame near batteries, especially when they are charging. The gas that escapes during the charging process is hydrogen…the same stuff they make bombs out of…very flammable. It is important to use the right tools and safety equipment as well as have knowledge of what to do when a dangerous situation occurs.

Warning!

Dropping a tool across the positive and negative terminal of any battery will cause it to short circuit, creating currents of up to several thousand amps. This will weld the tool to the terminal, destroying the battery and potentially cause severe burns. If a short circuit happens, get away from the battery as fast as you can. The area around the terminal will be extremely hot and an explosion and the battery may spark and explode. To safeguard against a short circuit, cover terminals that aren’t being worked on with an insulating cap and use insulated tools. Jewelry that might come into contact with the terminals should also be removed.

Overcharge

Proper charging techniques significantly decrease the likeliness of battery explosion. Excessive overcharging or improper charging parameters can cause the  battery to build pressure, cause irreparable damage and explode, possibly causing acid to spray from the battery. To prevent this from happening be sure to have proper equipment that is designed to charge deep cycle batteries. If using a solar array, wind or micro-hydro you will need a properly sized charge controller, if using a generator you will need a charger. Off-grid inverters usually have chargers built into them. If you do happen to get electrolyte on yourself it can be neutralized with baking soda and water, it is a good idea to keep some near the battery bank. If electrolyte gets in your eyes, force your eyes open under running water for 15 minutes, then call a doctor.

Don't Worry - Just be Safe

Ventilation of the battery bank is an important part in the design of an off-grid system. The ideal battery location is in a box that is vented outdoors with a fan. This way they are out of the way of accidental hazards and unlikely to cause corrosion of equipment or explosions from a spark or flame. A dangerous situation that might easily occur is disconnecting a battery terminal while  the batteries are charging or under load. This will likely create a spark upon disconnect and at a time when dense hydrogen gasses may be present. Verify that loads and charging sources are disconnected before servicing batteries.