Basic Electrical System Information
September 7, 2004
Copyright ©2004. All Rights Reserved - Ample Technology


Understanding how batteries operate is not possible without instrumentation to observe charge and discharge cycles. Even with instrumentation, correlating observations with performance is difficult for people not familiar with electrical systems. Knowing when a system is working as expected, and what corrective measures are needed if it isn't, isn't really an art. There really are rules which apply and when the rules don't apply then something is wrong. Which rules are broken determine what is at fault.

The EnerMatic Controller automates the production of energy, and provides the instrumentation to observe operation of the energy system. Despite the high level of integration and intelligence provided by the EnerMatic Controller, a user must still know how batteries behave under discharge and charge.

This publication is meant to help users of the EnerMactic System, but will be useful to all users of small energy systems. For more details and in-depth coverage, the books Living on 12 Volts with Ample Power, and Wiring 12 Volts for Ample Power are the definitive references.

A Full Battery

A battery can not be charged fully without some overcharging. Overcharging commences when the battery voltage rises to about 13.8 Volts during charging. To be more precise, overcharging commences when the electrolyte begins to bubble, which happens at about 13.8 Volts.

NOTE: All values are dependent on temperature. The values given here are applicable at 77 F, (25 C). Values also depend on the type of electrolyte, plate material and other design features.

The voltage at which gassing commences is called the gassing voltage. Given enough time at this voltage, the battery will fully charge. To shorten the time to reach a full charge a higher absorption voltage can be applied, typically 14.4 Volts.

Simply applying the absorption voltage doesn't result in a full charge. The absorption voltage must be applied until battery current has declined to a small percentage of the Amp-hour capacity of the battery. A typical percentage of 5% is used when charging from an engine, but a more accurate percentage is 1-2%, that is 1-2 Amps for a 100 Amp-hour battery.

Once a battery is fully charged, it can be floated to maintain that full charge. A usual float voltage is 13.5 Volts.

Amp-Hour Instruments and a Full Battery

How does an Amp-hour instrument know when a battery is full? By the parameters you program into it. The Ample Power Energy Monitor/Controller and the EnerMatic Controller provide two parameters called FULL V and FULL A, which stand for full voltage and full amperage. When the monitor sees that the voltage is above the FULL V setpoint, and then after the current declines below the FULL A setpoint, the monitor will reset to full.

The FULL V and FULL A setpoints are programmable because they are dependent on battery technology and how the battery is being charged. If those parameters are not set to reasonable values, then the monitor will not be able to stay in sync with battery capacity.

Amp-Hour Instruments during Discharge

Measuring Amp-hours is so simply accomplished that it was done well over 100 years ago using primitive motors which rotated at a speed relative to the Amps. By counting revolutions over a timed interval, Amp-hours could be calculated.

Today microcomputers have replaced the motors, but the principles remain the same ...measure Amps for a timed interval.

Unfortunately counting Amp-hours from a battery isn't always useful unless you also know the rate of discharge. That's because a battery yields less capacity the faster it is discharged.

In 1898, a researcher named Peukert discoved the relationship between the rate of discharge and the capacity which would be available at that rate. The relationship is exponential, which makes for some difficult calculations ... beyond the power of simple calculators. In 1989, the Ample Power Electrical System and Amp-Hour Monitor was the first to make use of Peukert's equation, calculating Amp-hours remaining in the battery bank, and at any rate of discharge. Today Ample Power products are still the only available instruments which directly calculate the exponential equation using Peukert's exponent to determine Amp-hours remaining.

To accurately calculate Amp-hours remaining, the exponent must be known. It takes two discharges to determine the exponent. Take the time to do the discharges and derive the exponent. In fact, do it every year and track how the batteries are aging.

Amp-Hours during Recharge

What comes out of a battery has to be returned to it plus some to pay the taxes on the second law of thermodynamics. Based on Amp-hours, 10-20% more Amp-hours have to be returned than was removed.

How much more has to be returned can only be guessed at until a history of discharge and charge is generated and from that an efficiency is calculated. Yes, that Amp-hour meter is guessing! All during the charge cycle, the display of Amp-hours consumed/remaining is a guess. What happens if the charge is terminated before the battery is full and discharging commences? More guessing is what happens. After a few more cycles of discharge and partial charge, the results shown on the meter are anyone's guess. You have to fix it with a full charge.

Ample Power instruments let you enter an initial efficiency guess. Over time, Amps in and out are accumulated and efficiency is recalculated. This is much easier stated than done. For one thing, efficiency also depends on the rate of discharge and the rate of charge, along with temperature.

Ample Power engineers have spent many hours addressing these and other issues, and while any claims of perfection would be laughable, given the complexity of the conditions, we think independent tests would confirm that our Amp-hour monitoring is the best there is.

Temperature Compensation

It might be a safe claim that all chemical reaction are temperature dependent. Certainly the chemical reactions occurring in a battery are dependent on temperature. The effects are most notable at the extremes, but even small differences can be detected.

Since the introduction in 1987 of the worlds first alternator regulator which compensated for battery temperature, Ample Power regulators have excelled at charging fast and full while extending battery life. More than 15,000 3-Step Regulators were sold in the late 1980s and early 1990s. Most of them are still in service and many are charging the same battery banks they were installed with.

This didn't just happen. Temperature compensation was taken seriously. Today, the same metal-to-metal temperature sensor technology is used to sense the internal battery temperature. Sensing external case temperature with a stick-on plastic sensor is cheap, but not very effective.

Temperature compensation has also lead to support activity. Many people have called from cold weather locales to report that their regulator is charging above 14.4 Volts, perhaps as high at 14.8 Volts. The inverse is also true. Cruisers in warm locales report that their regulator must have failed because it doesn't ever get above 13.9 Volts.

Temperature compensation is applied by the EnerMatic Controller. In the Regulator Status Report, the absorption setpoint may show as 14.4 Volts and yet the regulator is charging at only 14.32 Volts. The reason is also shown in the status report ...battery temperature is elevated.

Battery Charging/Acceptance

Battery chargers and alternators are current limited. That is, they can only produce a limited output current, say 100 Amps.

Large battery banks can often accept more current than a charger or alternator can produce. If this is true, then battery voltage will be less than the charger or alternator output setpoint. For instance, a 100 Amps alternator may not be able to drive battery voltage higher than 12.5 Volts even though the regulator setpoint is 13.8 Volts.

If a charge source is producing its rated output, and battery voltage doesn't rise to the charge setpoint, then things are normal, and battery acceptance is high.

The inverse is most often seen. Battery voltage rises to the absorption setpoint quickly, and current declines. This condition is symptomatic of two conditions; the batteries are already full, or the batteries are defective.

Battery Conditioning

Batteries which don't accept a charge can often be conditioned so that they will. This is particularly true of some gel batteries. This conditioning or breaking in the batteries is described in the Ample Power Primer.

Alternator Testing

Alternators are easily tested by first disconnecting the field wire from the regulator and then connecting the field lug to battery voltage. This is called full fielding the alternator and normally results in full output of the alternator.

Alternator output is dependent on RPM, so varying the RPM while watching alternator output is illuminating. If an alternator outputs under full fielding, then a failure to charge is upstream toward the regulator.

Battery Evaluation

Battery problems are the most common reason people call technical support. Most often battery voltage goes quickly to the absorption setpoints and current quickly declines. This is not a regulator problem. If the regulator/alternator can drive the batteries to the absorption setpoint then they are doing their job. The batteries are either full or unable to accept current.

Batteries which don't hold a high voltage overnight without any load connected are defective.

Batteries held at the absorption voltage without a decline in battery current to less than 2% of Amp-hour capacity are defective.

Batteries which are apparently fully charged but fall to a low voltage under load are defective.


All retailers selling Ample Power products are expected to provide reasonable support for their customers. That is, they are expected to be knowledgeable about the products and the common problems discussed in this document. They should be able to assist you via email or telephone communications, and resolve any technical problems.

In the event that a dealer is unable to resolve an issue, email support is available from See also the following websites for more troubleshooting suggestions.

Ample Power products are manufactured by Ample Technology, 2442 NW Market St., #43, Seattle, WA 98107 - USA