"Editor's Note: Due to the popularity of some of eHam's older articles, many of which you may not have read, the eHam.net team has decided to rerun some of the best articles that we have received since eHam's inception. These articles will be reprinted to add to the quality of eHam's content and in a show of appreciation to the authors of these articles." This article was originally published on: 02/14/2006
There is a lot of misunderstanding about the use of batteries in general, and in mobile operation specifically. Hopefully this article will address some of these misunderstandings. So we're all on the same field, and using the same game rules, there are a few terms which need to be defined.
There are literally dozens of different types of batteries. In this context we'll be discussing just one, and that will be the ubiquitous lead-acid battery. I recognize that some of the newer types are encroaching on our old standby, including NiCads (nickel cadmium), Li ion (lithium ion), and NiMH (Nickel metal hydride). While some of these types are used in vehicles, they are for very specific applications (hybrid vehicles come to mind), so we won't be discussing them here.Find out what works well at olg slots from the people who know best.
There are two types of lead-acid batteries amateurs typically deal with, as well as a few sub-types. The most popular SLI (starting, lights, ignition) battery is the flooded electrolyte one usually referred to as a plain old car battery. It's been with us for well over 100 years, and most everyone knows its general make up. A newer entry is the AGM (absorbed glass mat). It's only about 75 years old. Although there are minor differences between manufacturers, in all cases the electrolyte is a gel which is absorbed into a glass mat. In most designs, this mat and the battery's plates are spirally wrapped which greatly increases their vibration resistance. The matted design and gelled electrolyte further allows the AGM battery to be used in any position. If properly utilized, AGM batteries do not out gas which allows their use in non-vented areas like the trunk of a vehicle.
Although there are many battery companies making AGM batteries, I'm going to stick with just one; The Optima' series. The three types which will be discussed are the RedTop, YellowTop, nd BlueTop.
These product names are registered trademarks of Optima Batteries, as are the charts herein, and they are used with express permission from Stir Marketing, Optima Division's advertising agency.
Each of these flavors (colors) has a specific use, albeit the line between them is both fuzzy and ill-defined. It is the misunderstanding about which type to use, that is one of the themes of this article. The other theme deals with the connections of the battery to the vehicle's electrical system.
In general terms, the RedTop is designed for SLI use. Therefore, they deliver higher amperage than the other types, but for a shorter duration, just like we expect them to when starting our engines. This is the battery of choice for all mobile-in-motion applications, irrespective of a second battery and/or amplifier in use. They are considered discharged when their static voltage drops below 11 VDC.
The YellowTop battery is a special design offering attributes of both a deep cycle, and an SLI. Typical applications include mobile sound systems, hydraulic winches and tailgates (even low rider hardware), and as an SLI if properly sized 20 to 25 percent larger than a RedTop. They're considered discharged when their static voltage drops to 10.5 VDC.
The BlueTop battery is designed primarily for marine applications. Their strong point is their extended long storage capability which is much better than that of a RedTop if kept below room temperature. They have thicker plates, and an even lower internal resistance. These design features make them more expensive than the other two types. In most amateur mobile applications, this is NOT the battery of choice.
For example, if you're running a field day operation, or extended portable operation, the YellowTop is a better, less expensive choice. Even for emergency standby where the battery is kept on float, the YellowTop is still the one to use.
Because of its inherently low internal resistance (especially the BlueTop), an AGM battery has at least two advantages over a flooded, plane old car battery; they can be charged and discharged at very high rates. In a mobile scenario this is of minor concern as most vehicle charging systems can't supply much over 100 amps (usually much less) which is well within their maximum charge rating. As for current draw, there is a safety concern that should be noted. On a dead short an AGM of good quality can deliver in excess of 3,000 amps! Enough current in fact, to destroy the most robust of wiring schemes. This includes circuit breakers as their contacts will typically fuse together at this current level. Proper fusing is an absolute must for remote mounted batteries.
Some amateurs believe AGM batteries require special three stage chargers, which is not the case. The most important consideration is the maximum static charge voltage. Note that every manufacturer has different specifications with respect to rates of discharge, charging rates, charge levels, be it recharging or keeping the battery on float (constant low amperage charge). Thus, it behooves the user to research and apply these figures to what ever type of battery you use, lead acid or otherwise, if maximum service life is to be achieved.
All of these batteries have a finite charge/discharge cycle life. While they will usually outlast a flooded car battery in any application, continuing to discharge them past their rated discharge level (give or take 10.5 VDC), will drastically shorten their life. For example, repeatedly discharging one (intentionally or unintentionally) down to 9 VDC, will cause them to fail after a few dozen charge/discharge cycles.
If there is any doubt about what battery type to choose, allow me to reiterate. If you are using one as a primary and/or secondary battery, in a mobile-in-motion application, the RedTop is the battery of choice.
If this is a fixed station operation (mobile mounted or not), you're better off with a YellowTop if for no other reason than a cost/performance one. While a BlueTop will work in this application, the up-front cost is 40 percent more. There is another reason not to use one, and that fact will become evident further on.
Regressing for a moment, we have two applications in the subject matter; mobile-in-motion, and fixed station use (mobile mounted or not). These two applications require different wiring strategies. The former does not, nor should it, include any isolating devices. The latter does require an isolating device, and a very specific one, especially if the battery is a BlueTop.
Mobile-in-motion is seldom a battery-run application, although I know of a few amateurs who think this is a correct usage. It isn't, if you factor in the aforementioned charge/discharge cycle ratings, and the maximum discharge level ratings. It isn't the correct methodology to reduce RFI and EMI either. In any case, I'm ignoring this sub application.
Intermittent amateur use is exactly what the SLI battery is designed to do. It isn't the battery that is supplying the long term power, it's the alternator. The battery is only acting as a buffer. While most vehicle electrical systems have enough reserve to easily handle a 100 watt output transceiver, it's another story if we're running a power amplifier. Even if the alternator can handle the average load (about 50 amps in an average installation), the peaks will be over 100 amps which the SLI is happy to supply.
If the amplifier is trunk mounted, it is prudent to use a second battery mounted along side to handle these peaks which further allows the interconnecting wire to be smaller in size. When we use a second battery in this manner, it should be hard wired to the existing battery with only fuses in line to protect the wiring against shorts. If you think this is a bad idea, here is some food for thought; Just about every diesel pickup truck on the road that is equipped with a heavy duty electrical system has two batteries wired in parallel. In most cases, there isn't even a fusible link between them. In other words, no relays, and no battery isolators. There are a couple of really good reasons for this if you'll bear with me.
Fixed station operation requires a different strategy. Here if the batteries are hard wired together, they share the load and the level of discharge. Go a little too far, and you don't start your vehicle when the contest is over. In this application, some form of isolation is required. There are two types of isolation amateurs use, and they're both wrought with problems. Let's look at the isolation relay scenario first.
Aside from the complexity is adds, when the vehicle is started, and this relay is closed by what ever method, the alternator sees the load as a discharge below the SLI battery's actually discharge state. In the majority of the cases, the alternator delivers a higher voltage than would otherwise be necessary. If the primary SLI is of flooded design, this higher charge voltage causes it to out gas excessively. This can, and does, shorten its life.
Most amateurs assume they can prevent this occurrence by using a (cheap) battery isolator. These are no more complicated than a couple of diodes. About all they manage to do, is charge the batteries to a lower voltage. Depending on the unit and current draw, the voltage drop across them is between .7 and 1.4 volts. So instead of a nominal 13.8 VDC, the battery is closer to 12.8 volts. It also takes longer to charge both batteries even up to this sub-standard level. One way around this would be to adjust the alternators output voltage to compensate for this diode's drop. Almost without exception, the output voltage is fixed, and non adjustable.
There are special alternators and special isolators designed to work with them. They use remote sensing to measure the voltage (discharge level) of one or more secondary batteries, and supply the correct amount of charge current and voltage to each one. I can almost guarantee the average amateur won't spend the monies these systems cost.
Lets digress back to the alternator for a moment. The vast majority have build in regulators, and their complexity and capabilities are all over the map. They may or may not have maximum output voltage protection, or even current limiting. With one exception I'm aware of, none are designed to be used with an isolator. About the only place you ever see these is in recreational vehicles (where they're rare), and boats.
In all fairness, these systems work well enough so the average joe ham never relates any shortened battery life, or low voltage (or high voltage) problems to the vehicle's electrical system, irrespective of the wiring contained there in. Education can be a powerful thing if you apply it. Knowing that cheaply built, inexpensive isolators, connected to alternators not designed for their inclusion, can and will lead to problems, some of which can be expensive to fix.
Whether you use one battery or two, regardless of the inclusion of an isolating relay or any diode isolator, it is imperative that the wiring be regularly checked for integrity. I'll give you an example of why this is so important. Assuming you have your radio directly connected at the battery where it should be, and the positive battery clamp loosens, the alternator sees this as a battery discharge condition. It compensates by increasing its output (voltage). While the regulator in the alternator may contain some voltage limiting, it is nonetheless possible for the voltage fed to your radio to exceed it's rating with predictable results.
Direct battery connection is my last subject, but certainly not the least important. The debate over how to wire will continue long after I'm dead and gone. Nonetheless, lets take another look at the debate.
The first scenario is to connect the radio directly to the battery's positive and negative leads, with both leads fused. This is the exact methodology recommended by most automobile manufacturers, and most text books covering the subject.
The second scenario is connecting the negative lead to the same chassis point the battery's negative lead is connected, sans any fusing. There is a problem with this in the majority of the cases. To wit, the battery actually has four leads, not just two. Two of these wires are rather large, and run to the engine's block and the starter motor's solenoid relay. The smaller sized wires run to the aforementioned frame connection, and to the vehicle's power distribution system. If either of these smaller wires fail, current can flow through the radio's wiring harness, and/or through what ever commonality there may be through the vehicle's chassis and drive train. If the positive lead to the starting system fails, it may or may not cause a problem other than not being able to start the vehicle. However, the return for the alternator is the heaver negative wire. If it fails it might cause the alternator to act up. Whether it does or not, is moot. Regardless of your outlook on which scenario to use, my caution about keeping the wiring in good condition is paramount in either case.
There is one more item I wish to cover, and I thank Mark Brueggemann, K5LXP for this. Any auxiliary battery should be installed in a battery box and properly restrained. The rule of thumb for battery restraints is 6Gs lateral and 4Gs vertical. The last thing you want is a 60 pound battery flinging acid all over the insides of your vehicle! If you use a plane old car battery, the box must be vented to the outside.
Alan Applegate, K0BG
There are a few of finer points I want to cover. First, a second rear mounted battery isn't a necessity even if you run an amplifier. However, without one the wire size has to be somewhat larger to minimize voltage drop. In some cases, it is actually less expensive to purchase a second battery. For example, size 6 awg costs about .35 cents a foot, and size 2 awg is about $3 a foot. The latter is also harder to install.
There are several different styles of marine batteries including the BlueTop series. Some are meant to be used as an SLI, and others for deep discharge use like that imposed by a trolling motor. Still others are designed for sitting long periods of time without any charge applied. Looking at a battery's shape, size, or color is not an indication of which is which.
A common question might be, can the colors be mixed and matched? Yes they can if proper circuitry is used. However, some types are better suited for a specific application. While using a substitute may indeed work, it may be more costly from a purchase and/or life cycle standpoint. It pays to read the fine print.
During the research for this article I learned something I didn't know, and I want to pass it on. If you own a Honda product (including Acura) there is something very special about their alternator and it's control circuitry. As I stated above, most alternators have built in regulators, and their capabilities are all over the place. In every case except Honda, these regulators are essentially stand alone devices. The only thing the alternator needs is a power source to turn it, a battery connected to its output, and they'll generate power. Some are self exciting and don't even need the battery.
Hondas are different. There is control circuitry between the engine's electronic controls (EEC), and the regulator. This information is used to adjust the injector timing. Thus the EEC knows what kind of electrical (accessory) load is on the engine. For example, as the air conditioning compressor cycles, the injector timing is adjusted accordingly. While this system is designed to increase fuel mileage, it can play havoc with mobile amateur radio.
The interconnection doesn't seems to cause any problems with a nominal 100 watt transceiver. However, when you draw a lot of current (amplifier use, a second battery notwithstanding), this causes the EEC to enrich the fuel mixture. At highway speeds the resulting enrichment doesn't do much except cut the mileage a tad. At slow speeds it causes the engine to hunt (miss and stumble), and can cause the OBD II system to send an error code which turns of the "Check Engine" light. I've done this several times, and I thought it was RFI. Because the dealer charges $49 to reset the system, I purchased an OBD II compliant reader to reset the codes. Luckily it hasn't happened since, but fore warned is fore armed.
This fact also means that any after-market alternator must meet Honda's specifications. Be advised, none do even though their literature says otherwise. This information came from the chief engineer at Alternator Parts, and was confirmed by my local Honda dealer. By the way, if you're looking for a really BIG alternator, Alternator Parts makes the highest specific output unit available (see photo) in a standard frame size. It's rated at 250 amps continuous duty!