For years, the battery charger has been the stone simple, ferroresonant type consisting of a transformer which takes 110 AC and steps it down to approximately 13.8 volts AC. The AC is then rectified by simple diodes to DC charging voltage. Low price and reliability are clearly their strong suits.
In light of revolutionary microprocessor technology, however, the weaknesses of ferroresonant chargers are overwhelming. For example, ferroresonant charge ratings can be misleading because they are often based on output into a stone dead battery. While the battery is charged, the current falls off drastically, as the internal resistance of the battery increases. It often requires 24 hours or more to charge a battery bank. Any sulfation on the battery can fool the charger into incomplete charging. The low finishing voltages result in undercharging, particularly with deep-cycle batteries. Higher uncontrolled voltages would cook the battery. These simple chargers are extremely vulnerable to fluctuations in AC power that is so prevalent dockside and with gensets, further diminishing their effectiveness. If these chargers are left connected they can eventually boil out the electrolyte of wet cell batteries, as the typical 13.8-volt float voltages are too high for long-term storage. There have been numerous hybrids employing limited electronics, such as auto-shutoff, but they all suffer from the same basic charging inefficiencies.
Multi-stage smart chargers have been around for several years, and have matured into reliable products. The units we tested are an outgrowth of high frequency computer power supplies, in which a transformer can give full output at high charging voltages. The solid state regulator, typically a MOSFET, is controlled by a microprocessor. This leaves the charging profiles totally up to the program on the chip. Generally, there are three stages. The first is the bulk stage, in which there is a constant current charge at the rated output to a given optimal voltage. This is followed by the absorption stage that is a constant voltage for a programmed time or when the current absorbed by the battery falls to a specified level. The last stage is the float cycle in which the voltage drops to a level that maintains a full charge without causing electrolyte loss. Other algorithms prevent overcharging when the battery is under significant load, as well as many other electronic safeguards to protect the system and the battery.
Other advantages include twice the charging speed of comparable ferroresonant chargers due to much higher current throughout the charging process, and pure DC output for the best treatment of the battery. High frequency units can tolerate huge swings in voltage, typically from 80 to 135 volts (or 80-270 for multivoltage units) with no adverse effect on performance. Some units can operate like a high current, precision power supply even in the absence of the battery. Charging temperature may be optimized with a remote probe or built into the switch selections on the unit, further optimizing complete charging and battery health. These are genuinely meaningful adjustments. Lastly, voltage profiles of smart chargers are often user adjustable to accommodate sealed batteries that are becoming more popular and require different charging profiles.
Some chargers have additional stages, most commonly an equalization cycle designed to be manually started. Equalization is used for flooded cells to get rid of inevitable sulfate buildup and balance the cells within the battery for top performance. Equalization is normally done monthly on frequently used batteries, and involves charging the battery at approximately 16 volts at low current for a specified time or until a specified voltage is reached. The high voltage helps to convert sulfates back to active material. Equalization also mixes up the electrolyte to get rid of stratification (a natural process) for a more evenly balanced mix of electrolyte and better performance. This process is somewhat of a shock to the battery, so thats why it is done only at intervals.
Only two test units have equalization capability-Newmar and Statpower. Why only two? There are three concerns. First, equalization causes gassing. This means significant hydrogen gas is produced and extra ventilation is necessary for safety. Second, because the battery voltage is raised to 16-plus volts, any electronics left on may be destroyed, so its critical to be vigilant about shutting off any equipment before equalizing. Three, the process causes some loss of active material by shedding, hence the limited use recommendation. Because of these possibilities, many users steer clear of the process. Equalization is well worth the effort, but only for those willing to take the appropriate safety measures. Our belief is that most companies would rather avoid the potential problems for the relatively few people who want equalization.
Conceptually, smart chargers are simple, but electrically they are quite complex. The current is switched on and off (pulsed) thousands of times per second. Simply varying the pulse length controls the current. Early smart chargers had some reliability problems, but failures were analyzed and quickly rectified. For the tremendous benefits smart chargers offer, we don't think reliability is an issue. If a failure is absolutely unacceptable, a small, ferroresonant backup unit may be a consideration.
What We Tested
We obtained a mix of multi-stage, smart charger products in the popular 10- to 30-amp charging range, as well as two ferroresonant chargers for comparison. Our group varied from portable, single-battery units to three-battery units. Some required hardwiring while others merely required plugging in AC and tightening wing nuts on the battery. There are units for every need, so you can get exactly what you want. Many makers have more than a dozen choices. All units employed isolation transformers.
Considering the equalization issue, we also tested a charger with a unique capability called Pulse Technology, which bills itself as a way to keep sulfation from accumulating and to reduce sulfation in batteries already sulfated. This system is used in concert with a charger-either built in like the unit we tested, or as a small, stand-alone battery maintenance unit permanently wired to the battery or bank. (Large banks will require more than one unit). The pulse system is patented and basically works by subjecting the battery to evenly spaced DC voltage pulses to break down sulfation crystals. We tested the claim that this technology can revive badly sulfated batteries.
How We Tested
We used a BatTest 12-20, a microprocessor controlled battery tester to precisely discharge a deep-cycle battery to 50% capacity. We monitored the recharge cycle with a Fluke 867 graphical multimeter recording to a computer. Charger current was verified with a Fluke 36 AC/DC meter. The Fluke 867 scope waveform function was used to check charger DC output for purity and stability, as well as any superimposed AC leaking through. Because most of the smart chargers were able to charge up to three batteries simultaneously via separate hook-ups, we also tested a trio of batteries to make sure all were completely charged, regardless of the varying state of charge of each battery. We also observed some of the protective features such as spark suppression. Gel and AGM modes were also checked.
Radio frequency interference (RFI) was checked on the AM band from 150 kHz to 2.2 MHz . We used two AM units, one plugged-in circuit with the charging battery and one portable-both 10′ away. The FM band was also checked on commercial broadcast stations as well as the marine VHF, and ham FM bands. We also plugged in a color TV-one on the same circuit as the charger with external antenna, and one with a shielded cable hookup on a separate circuit.
With exception of the Pulse Tech World charger, all the smart chargers either met or bettered their charging specifications. Those smart chargers with multi-battery charging capability were smart enough to divide the charge up to differently discharged batteries, and to completely charge all. The smart charger outputs were clean and rock solid under varied AC input conditions. The two ferroresonant chargers were audibly noisy, charged much more slowly, and more importantly, did not charge nearly as completely. We found the ferroresonant units provided as much as 27% less charge in the same batteries under very carefully controlled conditions.
RFI was present in all chargers, including the ferroresonant units. The RFI was not detected on the FM bands at all, or on the cable-fed color TV on a separate line. If the RFI was only slightly noticeable on the in-circuit TV or did not block AM radio reception (but could be heard between AM stations) it was considered low. If the RFI blocked weak AM stations and was distractingly visible on the TV, it was considered moderate. None were severe. The results are noted in the Value Guide. Note that most RFI can be dealt with using filters, RFI shielding or both.
ChargeTek 2000 20-Amp
This small, 20-amp smart charger unit is oriented to trolling outboard motor users with the capability of being used in series up to 36 volts of three 12-volt batteries. It also works just great with one to three independent batteries. Its totally waterproof via rubber seals so it is just the ticket for open boats. The factory can custom fabricate AC or DC leads of any length, but the built-in AC and DC leads of 5-1/2′ should be fine for most situations. There are plenty of informational LEDs for charging current and charger status. It has virtually every conceivable safety measure built in, from over-temperature shutdown to protection from lead reversal, all of which is totally automatic, requiring no fuse replacements or user intervention-the simplest interface of all tested.
We couldn't confuse the multi-battery charging programming, so you can be sure all batteries will be charged regardless of varying states of charge among them. It reached a peak voltage of 14.48 in only 4 hours, 20 minutes-fastest of the 20-amp units. Float of 13.24 volts was fine for flooded cells. The factory in California will adjust it to any desired voltage if you have special, gel or AGM requirements. This is the only unit with a full two-year warranty.
Bottom Line: Recommended, but be aware of possible RFI with a TV in the battery circuit during charging.
Guest 2520C 20-Amp
This unit represents the latest and one of the most expensive in constant voltage, ferroresonant-type marine chargers with limited electronic controls and ignition protection. It is subject to all the same shortcomings of old technology, namely very slow charge times and incomplete charging compared to multi-stage units. It also put out only 5 amps into a 50% discharged battery-even when we used all three outputs to the same battery. Voltage stopped climbing at 13.11 volts after 18 hours, and held steady. It gave only 73% of the charge of the best smart chargers.
Bottom Line: The low cost $39 Schumacher 612A ferroresonant auto charger did a better, faster job. Not recommended.
Guest 2611 10-Amp
This semi-smart, 10-amp unit, while half the size and power rating of its 2520 sibling, charged more completely due to its multi-stage design. However, because the voltage charging profile has been compromised by being designed for both flooded and gel batteries without a voltage change switch, it is not optimum for either. The voltage climbed to a sub optimum 14.12 volts, then tripped to 13.4 volts, okay for flooded, but low for gel. The result was an 85% charge of a flooded test cell when compared with smart chargers using a voltage switch.
The 2611 is potted in waterproof, thermal potting compound, and while designed primarily for those using trolling motors, it will work fine for any open or wet environments. For trolling motor applications, it may be set up in series for 24-volt applications such as with two Group 24 or 27 batteries. It can handle up to two batteries in series or two totally independent cells such as a 12-volt starting and separate equipment battery. All the wiring is in place in the form of a 6′ AC cord and 4′ DC cords. It even has a fuse in each DC positive wire-a good idea, as was the bright green charged LED. Extension wiring kits are available from Guest. It is a very simple setup, low priced and rugged.
Bottom Line: Recommended where waterproof simplicity over maximum charging is the priority.
Newmar Phase III 20-Amp
This unit impressed us-from its gleaming stainless steel exterior to its very versatile performance. It put out 23 amps, three more than specification, and is designed for continuous, full output operation. A built-in brushless and filtered thermostatic cooling fan assures adequate air circulation, while reducing dust and salt accumulation inside. (It also means occasional cleaning of the filter.) It quickly adjusts from 110- to 220-volt input. The built-in analog ammeter was quite accurate, but more so at high power settings due to the inductive coupling found on all test units. It has an optional plug-in temperature sensor for maximum charging performance and battery safety. A very helpful optional remote status sensor panel also allows for charger reset when the charger has been subjected to prolonged high battery discharge conditions causing it to remain in the absorption mode. This time limit feature is user adjustable for system optimization and serves to prevent excessive electrolyte loss during simultaneous charging and high current usage. Other brands have this timer function but it is not user adjustable.
Another interesting feature is the power reduction mode that kicks in if the charger is subjected to elevated ambient temperatures to give reduced output without complete shutdown. It reached an optimal 14.49 volts during flooded battery charging in 6 hours and dropped to another optimal 13.4-volt float charge. A separate switch is used for gel charging, and was right on specification. It was also capable of performing as a precision power supply. Lastly, with minimal additional parts, the equalization function could be activated.
Bottom Line: All in all, this is a very well made and versatile unit. Recommended.
Professional Mariner Promatic 30-Amp
This unit, our most powerful test charger, is so small and light it almost defies belief. It has an aluminum, heat dissipating case and forced-air circulation via a brushless, thermostatic fan for heat control that allows it to run quite cool. It also can handle 110- or 220-volt power. Professional Mariner said that boatbuilders have installed more than 700,000 of their chargers as OEM equipment.
The Professional Mariner was right on specification for both gel and flooded batteries, and was the quickest charger, as would be expected since it is a 30-amp unit. It put out a bit more RFI on the in-circuit TV test than the other chargers, but it also was putting out 50% more juice. The built-in analog ammeter uses an inductive coupling similar in performance to the Newmar. There are several accurate, optional analog and digital meters that may placed conveniently for the skipper. This includes units that can view each battery separately.
If desired, the factory will adjust the output voltage for AGM batteries at time of purchase at no cost. Adjustments are user-accessible via removal of the drip shield.
Also, a remote temperature sensor may be attached to the battery, but is generally only needed under extreme conditions. There are more than a dozen different charger choices available. After the initial warranty, lifetime repair of the unit is limited to a maximum cost of 50% of the retail price of a current or equivalent unit.
Bottom Line: Recommended.
Pulse Tech World Charger 20-Amp
This unit appears to be an industrial quality product with a unique, patented capability called pulse technology. The charger is a portable unit with 6′ cables and industrial quality clamps. It works with either 110/220 volts at the flip of a switch, as well as with both flooded and gel batteries. It is not designed to be ignition protected, so it must be used with great care in enclosed places to make sure explosive fumes are not present or able to accumulate.
The built-in analog ammeter was accurate and appreciated. You may select both pulse and charge or pulse only. A timer delay is built in so you can connect a battery with no sparking even if the unit is switched on, a very desirable feature on a portable unit with repeated connections to batteries.
We found the pulse technology to be apparently beneficial in the three heavily sulfated batteries we had saved to test it on. In each case, improvements were noted in a gel cell, a flooded starting battery, and a combination flooded cell after subjecting each to several days of pulsing only before charging and retesting. We cannot call the results miraculous, but they were significant. Charging voltage, however, was higher than normally considered healthy for long-term battery use (15.5), and may have contributed to the favorable results.
We have serious concerns with the 15.5-volt peak voltage during bulk and absorption. Pulse Tech says this apparent voltage does not cause any problems with batteries because of the pulse technology that allows greater charge voltage without excessive gassing or heat. Further, this high voltage decreases with bigger batteries. This high voltage does not square with all we know of normal charging cycles where 14.5 volts is the normal safe, long-term peak. There were no provisions for external user adjustments to correct the voltage. It would be a good idea to check any new charger to make sure it is within specs. We would watch any battery charged by the World Charger very carefully for excessive gassing or heat.
The pulse-only modules are available in a variety of stand-alone units including solar, AC and battery powered, including a marine model. We see it as a possible alternative to equalization for sealed batteries.
Bottom Line: Until we gather more information on pulse technology, we are hesitant to recommend the World Charger. We remain a bit skeptical regarding long-term battery health, but don't want to dismiss a potentially beneficial technology.
Schumacher 612A 10-Amp
This ubiquitous $39 portable auto charger put out its rated 10 amps initially into the same 50% discharged test battery configuration used for all chargers. It has a 2-amp switch for even slower charging or for smaller batteries, as well as a 50-amp boost mode to help engine starting with a weak battery. Unlike the Guest 2520, however, it is not ignition protected. It only charged to 75% of the capacity of our test battery. It shut off when the battery had reached 13.9 volts after 12 hours, and came back on when voltage dropped to 12.9.
Bottom Line: Recommended as a cheap backup, but not for enclosed areas subject to explosive fumes.
Statpower TrueCharge+ 20-Amp
No charger has everything, but the Statpower unit is a showstopper in terms of versatility. We chose its predecessor as our favorite in 1996. This new, plus model adds quite a few improvements and added capabilities. If built-in options are what you seek, then this unit is for you. It is the only model with built-in user adjustments for three charging temperature ranges and they all work. But remember, the built-in temperature sensor reflects the temperature of the charger, so if it is in a different location than the battery the optional plug-in sensor should be used at the battery.
The Statpower is also the only model with both gel and AGM charging profiles built in. Some of the other manufacturers have a gel setting, but prefer to have the user let the factory custom adjust for special batteries such as AGMs, because there are a number of different charging profiles recommended.
The Statpower unit was the only unit with operational, built-in equalization-great for maximum battery life and performance-if you are careful. The equalization function is manually engaged on this unit (and with a bit of effort) to make sure you are well aware of what you are doing.
If you want a remote status panel, the Statpower has a very nice optional one that employs LEDs. It was the only unit with a two-stage charging profile option switch (no float), which is preferred for some golf cart-type batteries.
Lastly, we used the unit as a high current power supply (another switch selection), and found it to be rock solid and clean. It will even check your battery bank every 21 days and initiate a charge cycle if required.
If you need 220-volt capability, Statpower has dedicated 220-volt models available in the non-plus version which gives up the AGM charging capability.
Bottom Line: Our top choice. Highly recommended.
The Statpower, with all its bells and whistles, was again a dazzler. For the price its tough to beat. It is available in 10-, 20- and 40-amp versions, 12 volts only.
Our second favorite, the Newmar Phase III, was also very versatile, but a bit on the expensive side. Judging from the design, it should last a very long time. Newmar has a much wider selection of chargers, all the way to 70 amps, with 24-volt versions as well. Their well-written manual even explains how to hook up multiple units.
If small and powerful is what you need, then the Professional Mariner Promatic model excels. It is also available in 24-volt models. They too, have many other models to chose from, including an ultra sophisticated model with a fourth stage, which comes in 12-, 24-, and 32-/36-volt versions.
If you just want to plug it in and spin the wing nuts on the wires, then give the ChargeTek 20-amp unit a serious look. Even though the design is set up for up to 36-volt trolling motors, it will work just fine for other configurations up to three batteries-and its waterproof. No provision was made to charge more than one type of battery (flooded cells), but the factory will modify to any desired profile.
The only Guest unit we would consider buying in this test is the 2611, where waterproof units with low cost and ultra simplicity are the priorities. You give up some charging potential due to the compromised charging profile trying to do two things at once-flooded and gel. We did not care for the ferroresonant 2520-weak performance at a high price is not an attractive combination. Guest has many more models to choose from; wed stick with multi-stage models.
We were initially impressed by the Pulse Tech World Charger, but more concerned with the apparent high charge voltage. It has an industrial quality design, and has won an engineering innovation award. It may be breaking new ground, but until we have significantly more evidence, which is to be furnished by Pulse Tech from an independent lab, wed use it only on batteries larger than Group 27, and monitor them carefully for distress.
Lastly, we like the advantages of equalization. Its available only with the Newmar and Statpower.
Contacts- Chargetek, Inc., 2240 Celsius, Unit E, Oxnard, CA 93030; 805/278-4925; www.chargetek.com. Guest, 95 Research Pkwy., Meriden, CT 06450; 203/235-4421; www.guestco.com. Newmar, PO Box 1306. Newport Beach, CA 92663; 714/751-0488; www.newmarpower.com. Pulse Tech Products, 1100 S. Kimball Ave., Southlake, TX 76092; 800/580-7554; www.pulsetech.net. Professional Mariner, PO Box 968, Rye, NH 03870; 603/433-4440. Statpower Technologies, 7725 Lougheed Hwy., Burnaby, BC Canada V5A 4V8; 604/420-1585; www.statpower.com. Schumacher, Chicago, IL. Internet or mail order source for ChargeTek, Pulse Tech and other battery charging products: Unique Maintenance Products, PO Box 1703, Rogue River OR 97537; 800/362-5397 Order. 541/582-4521 Tech Info; www.4unique.com or www.batterymaintenance.com.