Hybrid Automobiles
Last Modified:
Mon, March 23, 2009
A lot of the material you read here was originally penned for publication on eham.net. The article didn't generate many replies, but it did generate a lot of amateur-related e-mail to yours truly, and more specifically from John Little, W9NET, and John Pavelich, VE3XKD. Both own Toyota Prius hybrid automobiles (left is a 2006 model), which is currently the best selling hybrid on the market. Some of the material was from these two, and I thank them for it.
The future has been written on the wall for many years. To wit; we have to reduce our dependency on fossil fuels, foreign or otherwise. The EPA, for what it is or isn't, has set standards for fuel mileage and emissions we all must meet. The automobile manufacturers have stepped up to the plate, and given us all manner of technical wizardry to improve mileage, and reduce emissions. Some of these new devices exacerbate the RFI we contend with. One of these, COP (Coil Over Plug), has become the number one bane of HF SSB operation. Unfortunately, there are more insidious demons creeping into our beloved mobile sanctuary. Enter the Hybrid automobile!
I don't know how many amateurs operate mobile, but I'd suspect the number is rather large. In a recent poll on the ARRL web site, the readers were ask what kind of HF mobile antenna they used (multiband or monoband). About half of the respondents said they didn't operate HF mobile (I'd like to see a similar question on VHF mobile). It's apparent a majority of amateurs operate VHF mobile, with a smaller number on the HF bands.
It really doesn't matter which mode or frequency, as all require some amount of current at a nominal 13.8 VDC (although we refer to is as 12 volts). Amperage requirements vary from an amp or two, to as much as 100 amps peak. All of this power is usually supplied by an alternator with the SLI (Starting, Lights, Ignition) battery acting as a buffer. In some installations, there are two or more batteries, and a larger alternator delivering as much as 250 amps. Twelve volts is twelve volts, and if you use good practices, installing mobile equipment is not difficult. I do my best to explain the correct procedures in the various articles on this web site.
The point to make here is, RFI ingress and egress comes from all manner of electronic devices, especially digital ones. It is safe to say that digital electronics made the hybrid automobiles possible in the first place. Most of us can remember the first switching power supplies, and the RFI they caused. Almost the same scenario has been played out with respect to the digital control systems in late-model hybrid automobiles.
John Pavelich, VE3XKD, sent me this URL. If you own a Prius (or any hybrid I suspect), you need to read the data. It may not be directly applicable to your specific hybrid, but I venture to guess that it is. While there are currently 20 or so hybrid vehicles available in the USA, the majority of them use controllers made by Toyota.
The Toyota Prius uses a Ni-MH battery pack. Similar to lead-acid SLI batteries, Ni-MH units are designed to provide copious amounts of power for a short duration, and can be charged at very high rates, with some in excess of 100 amps at 200+ volts! Other than the specific battery technology, the main difference is their nominal voltage.
The static voltage of an SLI battery is from 12.2 to about 13.4 (slightly more under charge), while the typical hybrid battery delivers 120 volts to as much as 750 volts (the Toyota unit is rated at just over 200 VDC). There are several reasons for the high voltage, not the least of which is an effort to reduce I2R losses, and the available current ratings of the requisite solid state devices needed to control all of the complex functions. I don't wish to get into these functions because they are beyond the scope of the article. Suffice to say, the battery pack voltage maybe higher or lower, the computer control may have different programming, but everyone of them is digital! Thus, the hash they egress depends on factors like those listed in the aforementioned URL.
I wish this was the end of the story, but isn't! The average hybrid has a small gasoline engine which uses modified valve timing to emulate the Atkinson cycle design rather than the more conventional Otto cycle design. Between the engine and transmission is a brushless, permanent magnet DC generator which (in most cases) can be used as a starter motor. There is the Ni-MH assist battery (it may utilize NiCads, or some other, even space-age exotic construction), a brushless permanent magnet DC drive motor-generator (AC in some systems) usually called the assist motor, and the all-important electronic control assembly. In some cases, there are multi-farad capacitor banks (16 to 64 Farads!). If you're really curious about how all of these parts work together, here is a report done by the Oak Ridge National Laboratory on the 2004 Prius. It's a 4.5 Mb in .pdf format, so it will take time to down load.
Digressing for a moment; there was a recent news article about capacitors that incorporated nanotechnology. The charge density of these capacitors are several thousand times that of current designs. If and when this technology comes to fruition, chemical batteries will become a thing of the past. Imagine a battery the size of a AAA starting your car?
If you're thinking about buying a hybrid vehicle, read all of the data on the particular model you can, as some of the data is purposely misleading no matter the manufacturer! This includes, but is not limited to, the application of included warranties, extended warranties, and assumed warranties especially with respect to the requisite assist batteries all hybrids require. While this may sound off the subject, it isn't. In a recent California Supreme Court decision, it was ruled that extended warranties cannot be considered an assumed warranty. By all means, read the fine print carefully, and ask questions even if the wording appears non misleading.
Here are a few things I think a potential buyer (read that amateur radio operator) should consider when purchasing a hybrid vehicle:
What size SLI battery (if any) is used? The SLI is usually quite small, and in most cases is not used to start the engine unless the assist battery is discharge for whatever reason.
Does the vehicle have a standard alternator to charge the SLI? If it does, what is its rating? I should point out here that unlike a non-hybrid vehicle, accessory loads like a rear window defroster may not indicated a reserve large enough to operate a mobile transceiver. It depends on the system strategies being used. Just because a Toyota Prius has enough reserve, doesn't mean every hybrid has enough.
How good is the RFI suppression? One way to tell is take along an AM radio (short wave if you have one), and listen on an unused frequency. This method isn't fool proof, but it is a start. If you can, talk to the Service Manager and ask specific questions about RFI. Most of the ones I've talked to have been rather evasive as if they know more than they want to admit. That wasn't the case at our local Toyota dealer here in Roswell, NM. They were very helpful, and even gave me the name and number of their local Toyota representative. The local Honda dealership (owned by the same folks), were equally helpful. Lets hope yours are too.
Contact others who have gone before you (like those I list). On line resources like eham.net are invaluable.
The one area that cannot be overlooked or minimized is the need for RFI suppression. I'm not talking about the items the manufacturer installed, but those you should install. In other words, hybrid vehicles require extra care in bonding, shielding, and installing split beads.
If you drive a hybrid, and operate HF (or VHF) mobile I'd like to hear from you about the trials and tribulations you experienced in installing your gear. If you've had RFI problems (ingress or egress), I'd like to hear how you solved them. In turn, I'll post them here with hopes that others won't have to suffer the same indignities.
Based on my e-mail correspondence with John Pavelich, VE3XKD, and others, it appears to be a herculean task to RFI egress proof a Toyota Prius. John plans to write an article about his travail to be posted on eham.net. Suffice to say, it takes a lot of time and effort, and I'm not sure how many amateurs would go to the lengths John has.
Hybrids are going to become even more prevalent in the coming months. Hopefully, manufacturers will step up to the plate and make their hybrids less noisy. Personally, I'm not holding my breath.