BATTERIES AND REGULATED POWER SUPPLIES
Adapted by Steve Medanic from
BATTERYPOWER FOR HO TRACKS
By Dave Ferguson and Gary Beedle
This article starts with a discussion on transformers vs. batteries originally written by Scale-Auto’s Dave Ferguson and Gary Beedle. While I agree with their concept that batteries are one of the best ways to improve your track I feel that they are not the only option. When Dave and Gary wrote this things were different. Today, well regulated and filtered power supplies are a good alternative to batteries and may in fact be superior. The original article debunked some originally poor ideas which is why it is used here. This adaptation hopes to do the same as well. Written from an engineering aspect by a DC power systems analyst.
THE EDITED ORIGIONAL ARTICLE: The editing added the sixth paragraph discussing wall wart output voltage and the associated graph. Otherwise the article is essentially reproduced as originally written.
Of all the questions we've been asked over the years, the one that has come up the most frequently is "how can I improve the power on my track'?" The solution is quite simple - use battery power! "That sounds difficult" you say? Well, it's not that difficult if you keep a few simple basics in mind
Because of their tradition of being home-oriented scale, most HO racers have developed a dependence on using a transformer for their power supply. Some racers even feel that a transformer is superior to batteries.
There is only one reason that HO sets are packaged with a wall-pack (a.k.a. wall-wart) as their power supply: it's simply the most cost-effective way for a manufacturer to get a power supply into a racers hands and enable him to enjoy racing. Other than that, power packs have very little to recommend them and in fact, are usually the limiting factor in a car's performance. Many times a racer pays too much attention to hopping up the motor in his HO car when he should spend it instead boosting the power output for the track. Think about it. Any armature with specs much hotter than a stock arm is going to be restricted by a stock wall-pack to such an extent that it will likely run SLOWER than a stock arm, overheat, or even refuse to run altogether.
Batteries can change all that and cause you wall-pack guys to look at HO racing m a whole new light. Batteries deliver clean current, free of any AC ripple, and can also eliminate the problem of voltage surge. If you're using a wall-pack now you've probably noticed the problem of voltage surge. One car on the track works fine but when a second one is added both cars slow down noticeably. If one car falls off the track the other one gets more power immediately. What's happening? In simple terms, your cars are drawing more current than the transformer is capable of supplying. In order to try and supply the necessary amperage, the voltage drops and, as a result, your cars have less power available and run slower. Not only will batteries allow your production cars to run better but they will also allow your HO car to achieve its maximum performance potential. But before we go further, let's look at the status quo, the transformer, a bit closer.
With even a stock out-of-thc-box car capable of drawing more current than a meager wall-pack can provide, it's obvious that a drastic improvement is in order. The most powerful wall-packs (or transformers if you prefer) available from either Tomy or Tyco is Tyco's #8775 High-Performance Wall-Pack, which is rated at an optimistic 22-volts and one amp. Please keep in mind that HO manufacturers rate their wall-pack voltage under no-load conditions. In other words, your car isn't on the track! That rated voltage drops a bunch as soon as you start running a car.
The following chart shows the typical voltage dips associated with a transformer, wall-pack or wall-wart. The voltages are typical of what can be seen from a standing start on a simple two turn oval track powered by a typical wall-wart. In this example when the car takes off from a stop the voltage can dip from the no load voltage of 22 volts to as low as 5 volts. The voltage rises as the car accelerates and levels off when the car is at speed. The voltage then rises to the no-load value when the driver gets off the throttle to brake for the turn. The voltage dips again as the driver picks up the throttle to go through the turn and accelerates out of the corner. The cycle repeats at the next turn. This example may be a bit extreme but it does show how the voltage on a non regulated power supply varies with load. Just imagine the impact that two cars will have on the voltage and how the cars would interact with each other!
Wall-Wart Voltage over a Lap
Batteries eliminate this issue as the power supply voltage will remain essentially rock steady throughout the lap. As we mentioned earlier, batteries deliver really clean DC power and virtually eliminate the dreaded power surges you may be experiencing. If that's not enough, you can now run any high-performance HO part you want and have it perform up to it's potential. So, now that we have you interested in battery power, where do you go from here'? Let's cover a few basics first. The accepted power norm in HO slot racing is 18-volts and since commercially available batteries come in 6 or 12-volt units you'll have to hook them up in series to obtain 18-volts. When hooking the batteries up in series you have two combinations to go with - you can hook up a 6 and a 12-volt or you can go with three 6-volts. Hooking batteries up in one of these combinations will get you 18-volts.
There are two types of batteries that you'd want to look at purchasing. The first type would be your typical car battery. These come in a variety of ratings with, usually, the more powerful batteries costing more money. What's a more powerful battery? Car batteries are rated by cold cranking amps and are generally available in increments like 200, 300, 400 or more amps. If at all possible, get the highest rated batteries that your budget will allow. Regardless of what rating you end up with, make sure the batteries are matched in amperage output as close as possible. If you use batteries with different ratings, your combination will only supply as much as the lowest-rated battery. (i.e.: if you have a 12-volt battery rated at 500 cold cranking amps and a 6-volt rated at 250 amps, the amperage available would only be 250 amps). The other type of batteries are termed "deep-cycle." These come in a variety of shapes, sizes, and ratings. Deep-cycle batteries are designed to have small amounts of power drawn over a long period of time. Deep-cycle batteries are typically used in marine applications (boats), golf-carts, diesel trucks, and any other applications where you need battery power but are unable to keep the batteries at a peak charge. If you can afford them, 6-voit deep-cycle batteries are the ideal set-up. They are usually more expensive than car batteries but due to their design they will last much longer.
SOURCES FOR BATTERIES. Besides the obvious auto parts stores and Sears, Wal-Mart and Sam’s Club, check your yellow pages for a battery shop. If you're interested in deep-cycle batteries check under marine supplies in the battery section of your yellow pages. Used deep cycle batteries can be frequently obtained from your local golf course.
MAINTENANCE. Batteries obviously require a bit more maintenance than transformers. A hydrometer will allow you to check the electrolyte level and specific gravity of the electrolyte on a periodic basis and your trickle charger will keep your batteries "pumped up" with only a few hours of charging a week. How often you need to charge your batteries will depend upon how often you race. A simple wall outlet "vacation timer" available at your local hardware store will allow the batteries to be charged whether you're there or not and will shut off the trickle charger automatically. A trickle charger is not a regulated and filtered unit and should be disconnected from the battery when racing.
That pretty well sums it up. We think you'll find battery power to be the best performance improvement you can do for your cars!
AND NOW FOR SOMETHING COMPLETELY DIFFERENT: Here’s where a few myths about batteries get debunked. This should not be considered as a slam against Gary and Dave. Their article made a number of good points which is why it was used. Unfortunately they didn’t perform an in depth study of batteries and the way they operate in the real world and some popular battery myths were presented. Analyzing battery systems is one of the things I get paid for and I have analyzed a number of large DC systems and participated in the development of engineering software that performs DC system analysis.
The above makes batteries sound so great why even consider anything else? Well . . . . As stated, batteries require maintenance and being a stored energy device their terminals should be protected from accidental contact with metallic objects. Batteries also contain acid, have a finite life and, as opposed to what is thought, batteries will not provide a constant voltage under load.
AMP HOUR CAPACITY: Gary and Dave mentioned Cold Cranking Amps. This is a measure of a batteries instantaneous output when fully charged and not a measure of its long term capacity. One method of rating a batteries long term capacity is by listing its Amp Hour capacity. Unfortunately the Amp Hour method is also not an accurate method of sizing or choosing a battery. There is more to it but the simple definition is that that a batteries Amp-Hour rating is the number of Amp-Hours of charge that can be removed from the battery at a specific discharge rate before the terminal voltage reaches the final discharge voltage as specified by the manufacturer. For a typical “Lead-Acid” battery the final discharge voltage is 1.75 Volts Per Cell (VPC). An 18 Volt battery is comprised of nine individual cells and 1.75 VPC x 9 Cells = 15.75 Volts. That final discharge voltage is a bit low for slot car racing. If the final discharge voltage is raised, then the batteries Amp-Hour rating has to be derated or reduced to accommodate the higher final discharge voltage. What that really means that a 100 Amp Hour battery may be only a 10 or 20 Amp Hour battery when used in a slot car racing application.
BATTERYVOLTAGE: A batteries output voltage is dependent on three factors: 1.) Battery Condition. 2.) Battery Load (amps) and 3.) The number of Amp Hours drained from the battery at the time the load is applied. A battery only contains so much capacity or Amp Hours of charge. As the batteries degrade over time, or due to excessive deep discharge cycles, the Amp Hour capacity will decrease. When you take the battery off charge ands start racing you start withdrawing from the available Amp Hours of energy stored in the battery. The batteries output voltage is dependant on the load AND the number of Amp Hours left in the battery at the time the load is applied.
Lets look at a test case using an ideal Plante’ battery (a battery having pure Lead plates). An 18V battery is comprised of nine individual battery cells. In the power industry, battery data and analysis is done on a per cell basis as opposed to a battery basis. A fully charged battery of this type has a no load voltage between 2.00 and 2.06 volts per cell. This equates to between 18 and 18.54 VDC for a 9 cell HO battery system. A typical HO “Lead Acid” deep cycle battery is a lead-calcium or lead antimony type which will have a slightly higher open circuit voltage. Despite its construction and materials a wet cell “Lead Acid” battery will have an end of cycle discharge voltage of 1.75 volts per cell (15.75 Vdc). The load should be removed when the battery approaches its end of cycle voltage. Running a battery below its end of cycle voltage can significantly reduce battery life and, if the discharge is severe, physically damage the battery.
Lets examine a Plante’ battery supplying the load of a group of HO scale cars during a typical race day using a typical battery. Under load battery voltage will initially drop to between 1.99 and 1.95 volts per cell (17.91 to 17.55 VDC). As the day continues and the battery is down to say half charge the voltage may range from 1.95 to 1.85 volts per cell (17.91 to 16.65 VDC). If the battery is almost depleted the voltage may range from 1.90 volts per cell to 1.75 volts per cell (17.10 to 15.75 VDC). Between races, when the load is removed, battery voltage will recover to approximately the fully charged no-load voltage, however, the battery is still depleted and voltage will continue to dip when the load is reapplied. Because a slot car battery has a slightly higher open circuit voltage the voltages will be slightly higher than indicated but the battery will still behave as described above.
BATTERYFADE: One of the worst cases of battery fade I personally experienced was at a state series finale way back when. The batteries were hot at the beginning of the day and the big motors were flying. I had a weaker arm and suffered in qualifying. During the day the battery pack faded dramatically and as the voltage degraded the relative performance of my weak motor kept getting better and better. At the end of the day that "toy" motor gave me speed over the big blocks and I took the win and the championship. A true but rather dramatic case of battery fade. I agree that these batteries were in poor condition. However, a set of batteries in good condition will fade as the day goes on.
In preparing for this article I measured the battery voltage throughout the day at the Restricted Open track at two separate HOPRA National Championship Races. In both cases the batteries were brand new deep cycle (marine/golf cart) units and were fully charged with plenty of capacity. Commercial automotive, marine and cart batteries are Lead-Calcium or Lead Antimony as opposed to pure Lead Acid. A Lead-Calcium automotive or marine battery has a no-load output voltage of about 19.1 Vdc or 2.12 volts per cell. In one case a regulated and filtered power supply with a 1-amp maximum capacity was installed on the battery to keep it peaked during the day. The battery had been charged overnight and the no-load voltage at the start of the day’s racing was above 19 Vdc. During each race the battery voltage would slowly but steadily decline as the 1-amp charger couldn't carry the load and the battery was slowly being depleted. It was interesting to watch the minute changes in battery voltage as cars accelerated and when someone came off. In this case the voltmeter was attached directly to the battery terminals and changes in voltage due to resistance in the tracks wiring was not observed.
During breaks between segments or between races the voltage would recover to approximately 19 VDC as the 1-amp power supply would charge the battery during the breaks. During each successive race the voltage would continue to decrease as the battery was being depleted faster than the charger could replenish it. During the last segment of the main, battery voltage dropped into the mid 17 VDC range. This was with a brand new Lead-Calcium battery set in combination with a 1-Amp power supply. Even though the voltage dropped by over 1 volt during the day at a National Championship event there were no complaints about power.
As stated earlier, battery capacity decreases with age. In a similar case, at a Midwest Series race I took both current and voltage readings on a track with a 10-Amp fully regulated and filtered supply connected to a typical set of used batteries that had been in service for several years. During that weekend the track was in continual use with practice, Superstock, Modified, Restricted Open and Unlimited racing. The voltage stayed rock steady at 19.1 VDC all weekend. The Unlimited race was last up and during the Unlimited main the power supply went from supplying a minimum of 1-amp during the breaks to in excess of 7-Amps at the end of each 5-minute segment. During the breaks the charger would roll the battery voltage back up to normal and the current would fall off from approximately 4-amps at the start of the break to about 1-amp just before the power came back on. In short the power supply was running the show and the battery was dealing with the peaks and helping to level the load for the power supply.
During the weekend there were no complaints about power problems or AC ripple until after the race when it was disclosed that a power supply was assisting the batteries. Then, of course, one individual used the power supply as an excuse for a poor performance. Sometime during the weekend we ran a practice session or two without the battery and nobody noticed.
The power supply had been tested and the ripple was well below 1% (0.18 Volts) at full load without the battery. At reduced load and with the battery installed the ripple was significantly less. Unfortunately, regulated and filtered power supplies have wrongly inherited the AC ripple badge that correctly belongs to wall-warts and transformers. There is a huge difference in the amount of regulation and AC ripple between the best wall-wart and an inexpensive regulated and filtered power supply. With a good power regulated and filtered supply there is no appreciable ripple and the voltage is rock steady all the way up to the units capacity.
RECOMMENDATIONS: From the Unlimited race example, my opinion is that a 10-amp regulated and filtered power supply should be able to handle any form of racing on a 4-lane track. A 20-amp supply would handle anything HO can throw at it for a 4 or 6-lane track. A typical RO or Unlimited car may require 4-amps on initial acceleration from a stop. The duration of this surge is measured in mili-seconds (1/1000 second) and most of the time the cars draw will be less than 2-amps. A 10-amp power regulated power supply should be able to accommodate 4 hot cars quite nicely. Any decent regulated power supply has good sized output filtering capacitors. These capacitors are stored energy devices and will provide the amps necessary for brief surges beyond the power supplies maximum rating. The power supply will provide continuous power at rated voltage up to its current rating.
The two types of regulated power supplies are the Linear and Switching types. The early generation of switching power supplies had to have a load on them at all times. That limitation is not the case with the newer switching supplies. Because of their larger transformers linear power supplies tend to be heavier and bulkier. In performance there is little to choose in performance between them. The thing to look at is the amount of ripple at full load. The lower the better. Ripple voltage less than 0.50% at full load (0.1V) is ideal.
Power supplies have come a long way from the ripple factories they were a long time ago and a track with a regulated and filtered power supply will work well for you. Some time ago I recommended a combined setup with both power supplies and batteries. I have now learned that with the right power supply batteries are not required.
I went to regulated and filtered power supplies exclusively many years ago and never regretted it. Since then I have added a second, conservatively rated, 20-amp switching supply operating in parallel with my original 10-amp linear power supply giving me a continuous capacity in excess of 30 Amps at 18.9 Vdc. With something in excess of 220,000 mfd (0.2 Farad) of capacitors in my power supplies I have a surge capacity well in excess of 50 Amps. These supplies have powered races of every class from box-stock to unlimited without a problem or toasted motor. Still think power supplies are junk? One of the best supplies available is the very limited production MaxPack supplies. Some of the tracks in the MARC series brag about their MacPack power supplies. I got the board for my 10 Amp supply from Jim many many years ago. It’s outlasted several battery sets and it’s still running strong.
RETHINKING COSTS: What about cost. A good set of batteries without chargers will cost in excess of $100. Good automatic chargers will quickly bring the bill to over $200. My power supplies were adapted from surplus units and were relatively inexpensive. Alan Galinko sells a nice 10-Amp unit for under $150 as does Trakmate’s Daniel Groulx. That price can be beaten if you are willing to look around and use surplus industrial units. My linear power supply was adapted from surplus equipment over 15-years ago and was relatively inexpensive.
CONCLUSION: A good power supply is a fine solution. With a good regulated and filtered power supply there is no appreciable ripple and the voltage is rock steady all the way up to the units rated capacity. Wall warts and other unregulated and unfiltered transformers are ripple factories with severe surge problems and should never be under a slot car track.
Batteries require careful maintenance and a good charger. They also have a finite life (5-10 years) and will eventually have to be replaced. The battery is a stored energy device whose voltage will vary under load. A battery is capable of providing a significant amount of current into a short. Batteries must be fused and the battery terminals protected to prevent an inadvertent short. If you must have batteries, invest in a 1 or 2-Amp regulated and filtered power supply as a charger. Leave the power supply connected to the batteries at all times. That way the power supply powers the cars, maintains battery voltage and charges the battery.
If you have to have only one or the other my opinion is to start with a well regulated and filtered power supply with at least a 10 Amp continuous capacity. Batteries in parallel with a 10 Amp, or better, regulated and filtered power supply will result in a truly awesome setup.
Steve "Maddman" Medanic