How big a battery bank do I need ?


For most people to answer to this is "as big as possible". For example, Charlie Wing's book the "Boat owners Illustrated handbook of Wiring" has a very good explanation of how to calculate the capacity you need. The calculations start by working out what your daily load will be both at anchor and while underway.
You need to remember that you cannot use all of the capacity your batteries have without shortening their life considerably. You should aim to not discharge your batteries past 50% of their capacity. In addition if you are charging batteries from your alternator while underway you will find that the last 20% of the charging cycle is painfully slow. All of this means that the amount you have to work with for continued operation while underway is 30% of the rated capacity of your batteries.
So for example to provide for a consumption of 120 Amp Hours per day and charge once per day you would need to have a battery bank rated at 400 Amp Hours.
Every boat will be different of course and you will have to make a best guess at the answers. You should do a separate calculations for when underway. Often at anchor the loads will be higher as there are more lights left on for longer times and they are not offset enough by lower navigational equipment loads.

Phone: 813-601-2922

E-mail: [email protected]


Should I hook up batteries in Parallel or keep them in separate banks?

There may be small disadvantages to hooking up batteries in parallel but there are also considerable advantages.
The main disadvantage is that as the batteries get old one will quite likely eventually develop a shorted cell. It will very quickly damage the other batteries by causing them to be overcharged by a charger and then discharged trying to charge the shorted battery.
One way to guard against this is to use an Amp Hour meter and measure the calculated efficiency of the batteries from time to time. Any drop in the level could indicate a bad battery.
The advantage of having them in parallel is that it makes a larger battery bank which will be less discharged in percentage terms and so will have more cycle life.(last longer) It will also make a simpler electrical system, less switches, combiners, expenses.

Phone: 813-601-2922

E-mail: [email protected]



Which alternator is right for my charging system?

Alternator selection depends on three primary factors. The first factor is mounting configuration and physical fit. Most marine gas and diesel engines will feature one of four mounting types, compatible with one of four alternator mounting styles; 1" single foot (Motorola-style), 2" single foot (Delco-style), import (Hitachi) style saddle mount with 3.15" between front and rear feet, and J-180 style saddle mount with 4" between front and rear mounting feet. The Balmar Product Guide (click here) features an application chart that matches many engine types to alternator mounts.

Keep in mind, though, that mounting styles may vary based on engine year and model. A visual inspection of your specific engine and existing alternator is the most dependable method for ensuring a proper new alternator fit. Dimensional drawings for all of our alternators are available on our website. Be sure to identify any engine components which could conflict with the alternator case or output connections at the back of the alternator.

The second factor in determining proper alternator fit is to match the alternator's output to the width of the engine's drive belt. If your engine uses a single 3/8" (or metric equivalent) belt, the largest recommended alternator will be 80 amps. A single 1/2" (or metric equivalent) belt can support up to 110 amps of alternator output. Dual 3/8" or larger belts can support up to 200 amps of alternator output. Any alternator loads in excess of 200 amps will require dual 1/2" or larger belts.

The final factor is battery capacity. In an ideal world, alternator choice would be determined based on the factors above, prior to selecting batteries for the vessel. Unfortunately, batteries are often installed before the alternator is selected, so we're limited in our ability to control this part of the equation. If, however, we do have the opportunity to consider battery size when selecting an alternator, a good rule-of-thumb is to size your alternator at approximately 25% to 40% of your desired battery capacity.

If your intended battery capacity demands greater alternator capacity than the first two factors allow, it may be necessary to look at upgrading pulleys and/or brackets to support a larger capacity alternator to meet battery needs.

*What horsepower load will I put on my engine with a new alternator?

Typically, when an alternator is working at full output, it will require approximately one horsepower for every 25 amps it produces. As such, a 100-amp high-output alternator will demand up to four horsepower to operate.

Does belt choice affect alternator performance?

Certainly, belt quality will have a dramatic affect on both alternator performance and the life of the belt itself. We find that high quality belts, such as the Top Cog belt by Dayco or the Green Stripe belt by Gates, will provide the best performance and longest life possible.

Keep in mind, the width of the belt limits that belt's horsepower capacity. As a result, any belt -- no matter what quality it might be -- will fail before its time when the alternator load exceeds the belt's capacity. Once again, if the belt is narrower than 7/16", the maximum amperage load we can safely carry is 80 amps. If the belt is 1/2" wide, 110 amps is our upper limit. Any alternator in excess of 110-amp output will require dual belts.

Phone: 813-601-2922

E-mail:[email protected]



Do I need a case-ground or an isolated-ground alternator?

In most marine applications, the engine block becomes an integral part of the vessel's grounding system in which case, the case of the alternator will also become a part of the system ground. As such, it makes perfect sense to allow the alternator mount to be the conductor on the negative side of the system.

Some vessels may not benefit from the engine being a part of the system ground; specifically metal boats, which could suffer from a variety of corrosive factors if the hull were to become a conduit for ground. In addition, many newer engine models utilize computer-controlled ignition systems which can be negatively impacted by unintended grounding.

The majority of Balmar alternators are available in either case ground or isolated ground configurations. Case ground alternators, like the name implies, utilize the connection between the alternator and the engine block to complete the negative link to the battery banks. Isolated ground alternators, in contrast, keep the ground side of the alternator completely separate from the alternator frame, so grounding is restricted to a cable that can be directed toward the system's central ground source.

If you are unsure as to whether your system uses an isolated ground or case ground alternator, we recommend using the isolated ground unit. Typically, though, any system that includes a ground connection at the engine block will be compatible with a case ground alternator.

Phone: 813-601-2922

E-mail: [email protected]

How do I charge two battery banks and still keep them separate?

There are five ways of doing this:

*The simplest way, if you can remember to do it, is to turn your battery switch to "BOTH" when charging, and turn it back to 1 or 2 when you are finished. This solution is risky for those who sometimes forget and then end up with a flat battery from time to time. If you want to automate the process and make it idiot proof, then you need to pick one of the other options.
* The best way, if you can manage it, is to have two alternators. This allows independent charging of each bank, and by fitting a combiner switch you get the added feature of a backup alternator for either bank in the event of a failure.
* The wrong way is to use a battery isolator, which is a set of diodes which allow the charge to go to each battery but doesn't allow the batteries to connect to each other. The big problem is that there is a voltage drop across the isolator means you need to have an externally regulated alternator with a voltage sense wire downstream of the isolator. Another problem is the high failure rate of isolators. Another is that the voltage drop means wasted energy.
* A good and successful way is to use a battery combiner such as the Blue Sea ACR This is a voltage sensing solenoid which connects the batteries together when they are being charged and separates them when they are being discharged.
* The fifth way is also a good way. Using either the Xantrex Echo Charge or the Balmar Duo Charge you can charge the start battery from the house bank. These relatively simple devices give a controlled low amp charge whenever the house bank is receiving a charge.

What is a galvanic isolator and why should my shore power system have one?

A galvanic isolator is a device used to block low voltage DC currents coming on board your boat on the shore power ground wire. These currents could cause corrosion to your underwater metals; through hulls, propeller, shaft etc.

Boats in a marina plugged into shore power all act as a giant battery. They are all connected together by the green shore power ground wire, which is (or should be) connected to their DC grounds, engine block, and bonded underwater metals. If the boats are in salt water then that forms an electrolyte and the dissimilar metals connected together act as a battery, causing corrosion.

The galvanic isolator has two pairs of diodes set up so that a voltage of about 1.2 volts is required to cause them to conduct. As most DC voltages caused by galvanic action will be less than this, they are blocked. Good quality isolators also contain a capacitor, which only conducts AC current, as a backup.

Normally no AC current is carried on the shore power ground wire, but it has to be able to carry the full load of the circuit in the event of a fault. Therefore it is important to have a good quality unit that will not overheat when required to carry the rated load. Some heat will be generated by the voltage drop and the unit must be able to withstand this.

As the galvanic isolator fulfills such a key function in the AC circuit it is only prudent to use the best quality unit available.

Phone: 813-601-2922

E-mail: [email protected]

Which is better, a generator or an inverter?

A generator is essential for heavier loads like air conditioning but they do not run well with light loads (Prolonged running with light loads causes the cylinders to coke up) Generators are noisy and expensive. Inverters are best for intermittent heavy loads or extended light loads. Prolonged running of heavy loads would be too big a drain on your house batteries. The ideal setup is to have both a generator and an inverter. Run the generator when you need some real power, run the inverter when you want to heat up a cup of coffee.
People are wearied of inverters sometimes because of the power they draw, but you have to take it all in perspective. A heavy load for 1 minute to heat something up isn't a large number of amp hours out of your daily budget. Leaving your anchor light on all night uses much more power. An added advantage of many inverters is that they often incorporate a heavy duty charger.

Phone: 813-601-2922

E-mail: [email protected]



Do I really need a high output alternator on my boat?

If your vessel's DC system is limited to a standard flooded starting battery that supplies minimal house loads, your engine's standard alternator will probably be sufficient. On the other hand, if your vessel features multiple battery banks, substantial house loads and/or inverter loads, or battery technologies like AGM, gel or deep cycle flooded batteries, you will see a great improvement in your vessel's charging performance with the introduction of smart regulation and a high-output alternator.

Phone: 813-601-2922

E-mail: [email protected]

How to test a galvanic isolator that doesn't have a monitoring system?

Galvanic isolators are a bit difficult to test. Current ABYC standards require that galvanic isolators be self testing. For testing older isolators without this feature there are a number of methods that can be used, the one that follows is one that I found most useful.
Unplug the boat from shore power before starting the test.
Disconnect one lead of the isolator so that you are testing it only. Get a digital multimeter set to the diode test function. Put one lead on one side of the isolator and the other lead on the other side.
As the capacitor starts to conduct current the reading should rise to approximately 0.9 volts. Remove the test leads, short the two wires of the isolator together to discharge the capacitor and repeat the test with the test leads reversed. You should get the same answer.

Interpreting the readings:

* If the reading is instantly 0.9 volts then the capacitor is defective or there is no capacitor.

* If a voltage of 0.45 volts is observed one of the diodes is shorted.

* If there is a reading of 0 volts then both diodes could be shorted.

* If there is a reading in excess of 0.9 volts then one or both diodes are open (not conducting) in which case you should stop the test before the capacitor reaches 2.0 volts or you will damage it.

Phone: 813-601-2922

E-mail: [email protected]



What makes Balmar alternators and regulators so special?

In order to really understand the difference between Balmar charging equipment and the average alternator and regulator, it's important to understand our goal in designing and building a Balmar alternator.

In an automotive application, the alternator's function is to keep a starting battery happy while supplying power to electrical/electronic operations needed to operate the vehicle (i.e., headlights, cassette deck, vanity mirror lights, etc.). In this environment, a simple, internally-regulated alternator is usually more than sufficient to get the job done.

In the marine environment, the alternator and regulator must support a much greater battery capacity to fulfill engine and house battery loads. The alternator and regulator must also be able to charge effectively at lower rpms and live in an inhospitable environment. In addition, the alternator and regulator may sit for long periods between uses (surprisingly, one of the toughest aspects of alternator life). At the same time, this system must meet the expectations of boaters that want to have their batteries charged within the least amount of engine run time.

To meet those challenging conditions, a high-output marine alternator begins with high amperage diodes, larger, higher-quality bearings, and a durable frame, that's protected against potential corrosion damage. Balmar applies a durable powdercoat finish to protect the alternator from rust and corrosion.

Another thing that sets a Balmar alternator apart from the rest, is the technology we use to create our rotors and stator windings. The rotor/stator combination is the primary factor in controlling the amount of top-end output, low-end output and cut-in level (how slowly the alternator can turn and still make useable amperage). The rotor and stator combinations in Balmar alternators are custom wound and calibrated to maximize output, not just at top end, but also at the low end of engine rpm.

But, that's just half the story ...

Balmar has been one of the industry leaders in creating intelligent voltage regulation that enables us to meet the needs of newer battery types, and the added load that modern electronics and inverter technology demand. Intelligent regulation, like that provided by our Max Charge and ARS-4 regulators, matches the output of the alternator to the specific needs of your batteries (AGM, gel, Optima, deep-cycle flooded, etc.) so batteries charge faster based on the needs of their unique constructions, and we can most effectively utilize the added capabilities that our alternators provide. And we've done it in a way that doesn't require the end user to be an engineer to get the most out of their charging systems.

In addition, many of our voltage regulators are equipped with the ability to monitor both battery and alternator temperature, and respond by increasing or decreasing voltage levels to maximize both safety and performance. In the event of a condition that poses danger to the system or the vessel, the regulator has the ability to discontinue charging completely. These systems are really very smart.

Phone: 813-601-2922

E-mail: [email protected]