How to install a GPS on the motorcycle
Last update: 10 Jan 2003
CHOOSING A GPS MOUNTING
First, you have to look for a mounting bracket. Most GPS manufacturers offer such an accessory. They don't feature any vibration damper. So, if you intend to install it on a real on-off motorcycle (say, KTM LC640, par example) or if, generally speaking, your "menu" includes some serious off-roading, then you have to go with a vibration dampened bracket like those offered by TOURATECH.
INTERNAL OR EXTERNAL POWER ?
Then you must start to worry
about powering the unit. Internal batteries are not suggested for off-road usage since the tend to loose contact at large
bumps. So you have to connect the GPS to vehicles electrical installation. Besides, it is much more economical and environmentally
friendlier than the alkaline cells (recent NiMH rechargeable cells provide good mileage but they do poorly at low ambient
temperatures) while ordinary dry cells must be avoided because of their tendency to leak.
Another advantage from using the vehicle's electrical installation is the ability to operate the GPS just for fun. No battery
drain out concerns! But you have to purchase a power cable from either the manufacturer or (for GARMINs) a
Pfranc distributor who is much cheaper anyway.
PROTECTION FROM VOLTAGE SPIKES
You may think that, if your GPS unit suggests 10-32V external supply, then you can safely connect it
directly to a motorcycle's 12V installation. This is wrong. It seems that in the portable
GPS receivers there isn't enough space for the bulky coils and/or other voltage suppression
devices. So you must add external components for filtering out the
harmful negative and positive voltage spikes (in excess of +/- 100 Volts,
durations up to a few milliseconds). Thanks to Mr. Tony Broad of
GARMIN we have a confirmation:
Hi Dimitrios,
There is no spike protection in the GPS - you can create you own by wiring a large capacitor and diode, as per
the attached diagram.
Regards,
Tony Broad
Service/Support and MIS Manager
Garmin (Europe) Ltd
Quite a few people supply their gps units without any overvoltage protection measure. While this might work without reliability problems, it depends on the motorcycle and the gps supply wiring. And remember, while engine operates, a shudden removal of the battery will produce fairly large voltage spike on any motorcycle.
The above suggested circuit consists of only two components, thus it's very easy to built. Its main drawback is the bulky capacitor. There will be a large current spike when connecting it to the power, so you have to use a slow-blow fuse. This initial current surge makes it unsuitable for powering from a relay contact (you do need a relay, if you are unable to find a switced supply voltage on the motorcycle). Alternatively I suggest the following circuits:
- A simple voltage suppressor (8.2KB gif image) with a special zener suppression diode. This is the circuit I use on my own motorcycle (photo will added in the future).Or,
- An "automotive range" "low dropout" voltage regulator (10.3KB gif image). This is designed for GPS units requiring either 5V (like GARMIN GPS-12) or 10V minimum (like the GARMIN GPS-III+, GPS-12Map or GPS-12XL). The 5V version can operate even in a 6V installation. However, for units needing 10V min. I suggest the circuit 1. There's no need for an ic-regulator in that case.
- For GARMIN eTrex and eMap, use the above circuit with a modification: ic identified as REG must be a LM2937ET-2.5. Output voltage will be 2.5V, enough for the operation of this kind of units.
CAUTION: circuits 2,3 are not intended for permanent connection to the battery, since they draw a few mA of quiescent current, even when the GPS is off.
In any case, you must install a fuse in series. A 0.3A one should be fine, since the usual current consumption is less than 100-150mA (about 60 mA for the GPS-12Map, including backlight).
If you have any question regarding to the above circuits, feel free to email me (see start page). And be sure to make correct electrical connections, otherwise you may damage your GPS!. To be on the safe side,
first test your circuit outside the motorcycle: standby current (no GPS) must be less than 10mA and the output voltage should
be within 5% of nominal voltage (with or without load). Watch out for the GPS power input polarity!
The circuits 2&3 must be enclosed preferably in a metallic enclosure for better heat dissipation (not a big issue though).
This is more true for the low voltage versions. But if you do so, you must insulate the box from the circuit. Even if using
a plastic enclosure, fasten the circuit with large quantity of thermal glue (silicone) to protect it from vibrations and
moisture.
ADDITIONAL MEASURES FOR MOTORCYCLES WITH AC VOLTAGE INSTALLATION
Some motorcycles that don't have a battery don't also have a rectifier. Thus, their electrical installation provides ac
voltage. Portable GPS devices cannot use that voltage. In order to supply the GPS unit, ac voltage must be properly
rectified and regulated.
To rectify the voltage, use an ordinary high voltage bridge rectifier (from any electronic spare parts store), or build your own using four 1N4007 diodes. No need for bulky motorcycle rectifiers because current
drawn from any GPS device is fairly small (in the 100mA area). Because of the increased C1 capacitance, it might be required
to increase the fuse rating (or use a slow blow variant), because the initial charge current will be higher. The circuit
should look as following:
10V or 5V "low dropout" voltage regulator for motorcycles with ac electrical installation (10.3KB
gif image)
As a final note, read diagrams carefully and use at your own risk!