fuse rating required for Garmin 89/90/92 cigarette power adaptor

[gabu]

Sorry Gents/Ladies not for if I'm in the right area for asking this, but recently I've required a Garmin 89 GPS unit on ebay pretty cheap as it happened, for some cross country flying in South Africa.

The guy who sent it in the post also providing a combined data/power cable. Unfortunately the physical ciggerate adaptor is missing i.e. I have 2 wires. Its easy enough for me to get hold of the ciggarette adaptor but acquiring the correct fuse rating is begining to remind me of my ex-girlfriend (a total bitch).

The Garmin web site isn't much use

I'm just wondering if any of Gents has or has owned the 89/90/92 units & can help. Or can suggest any other Avenues to expolre.

Regards

[down&out]

Don't have the actual unit, but I can help with the maths - so you can work it out - I think..

W=IV (W= watts, I = current & V = volts)

Therefore I=W/V. Knowing the voltage of your a/c (12v?), look at the power consumption (in watts) of the unit (almost always printed on the back, or maybe available in technical specs on the web). Plug the numbers into the formula above and you will get the average current. Add say 25%-50% and get a fuse at that rating.

(PS It was a long time since I did my Physics at school, so if anyone spots a problem with above, feel free to enlighten us!)

PPS I'm guessing your unit may draw up to 1w (My GPSIII handbook quotes 0.5w max). So using the above formula, I'd be looking for a fuse aroung 0.1A -0.2A. I'm sure there wouldn't be a problem going for a bigger one - the main thing is to stop a fire if your unit packs up and I can't see one starting with such small currents (+ you'd see it pretty quick yourself)

[Keef]

If the unit has rechargeable batteries in it, it's quite likely that it will try to recharge them at the same time as it's running, and that could draw 500mA or so, on top of the unit itself.

The colour units pull quite a lot of current (and eat batteries); the monochrome ones a lot less.

I'd just plug in a one amp fuse, and leave it at that.

[Fujiflyer]

gabu, do you mean (as I assume) that you have the lighter socket part (ie the lighter receptacle) as a fixture in your a/c? If so that should be fused at no more than a few amperes - this maybe on the circuuit breaker / fuse panel or (if the lighter was added as an "extra") may be an inline type fuse holder tucked behind the panel, in with the wiring loom.

If you want to add an extra fuse in your lead then as Keef suggests 1A is about right. An antisurge (slight time delay) type would probably be best. You may already find though that the lighter supply is fused at a similar level - a real lighter draws in excess of this but these sockets are often only fitted in a/c for external equipt such as yours.

Rich

[RW-1]

The Garmin web site isn't much use

Perhaps, but did you use the sales form to query them? Garmin Technical Support is one of the best, with your unit ID and question they could tell you exactly what fuse should be in it.

[gabu]

Thanks everybody, I was guessing at a 0.5Amp to 2Amp fuse, but I'm just to do as the last chap suggested by running a technical query with my product ID thru' to Garmin, seems a pretty sound idea.

If they help they help if not it time to do the maths!!

Good to know there are helpful and willing people out there.

Thankyou.

[Circuit Basher]

The manual on the Garmin site (http://www.garmin.com/manuals/204.pdf) indicates that the current drawn from the batteries is 0.16A max. As there are only 4 AA batteries, the voltage will be 6V and current drawn is thus doubled compared to a 12V supply. External supply limits are quoted as 10 - 40V.

If it were mine, I would personally put a 1A fuse in the cable and think no more about it. If you've got any doubt at all, then power the GPS from a car cigarette lighter and use an ammeter (if you have access to one) to measure current drawn (with backlight on). A 1A fuse is not going to cause a great risk of electrical fire / equipment damage in the event that you manage to short the plug out.