Hot Shot Question for electronic experts

[Oldav8tor]

I use a John Regan Hotshot battery charger in my '17. It easily keeps my Odyssey 12 volt battery charged. A question.... I run a old Garmin GPS for a speedometer / odometer. The two Garmin's I've used were about 10 years old. The first one went for over 3000 miles and quit. The second for a few hundred. The failures may be simply age-related or is something else going on?

I understand the output from the Hotshot is 1/2wave pulsating DC whose voltage varies with the engine speed and wondered if that being added to the pure DC from the battery might have a damaging effect to the GPS over time? I connect the GPS to the DC circuit thru a USB adapter that drops the voltage to 5 vdc. Would a filter capacitor in advance of the USB adapter be a good idea or am I worrying over nothing?

[TRDxB2]

Electrical components usually fail after several hours or after a long time. If you ran the first GPS for 3000 miles with the same setup, Hotshot & USB adapter, then it sounds like all is well (unless you changed something for the second GPS, different USB). If there was an issue I would assume the USB adulator would go first. Have you tried an different USB adapter with the second GPS to confirm its not the USB? Did you test the output voltage of the USB adapter at a faster idle to see if its output voltage changed?

[Oldav8tor]

Frank
I suspected the first USB adapter and replaced it with one designed for 12-24 volt marine use. I’d like to test it but need to figure out how to connect to the + lead in the USB connector or cable. My electronic education dates to the vacuum tube era so I’m not up on the latest stuff. I used to build radios… now I’m lucky if I can operate them.

[TXGOAT2]

The battery ought to absorb the voltage peaks and fill in the valleys. Putting a high value capacitor in series with the supply to the Garmin would probably further smooth out the current flow. I am running a Garmin device off a small 12 V lead acid gel battery, but there is no connection to the car's system. I've gone 4 - 5,000 miles with no trouble so far. I use the suction cup device to stick the thing to the windshield, and plug its adapter into a cigar lighter socket wired to the 12 volt battery. The internal Garmin battery is about useless. It can't support the 3X5 screen for any length of time. The small 12 V gel battery will go a long time without attention. The car is a 1927 roadster with starter, functioning magneto, buzz coils, and 6 volt generator.

[MKossor]

Putting a high value capacitor in series with the supply to the Garmin would probably further smooth out the current flow.

Putting the capacitor in SERIES would render the charger inoperative. I believe you meant PARALLEL with the battery supply as that would aid in filtering out voltage transients and noise.

I agree the USB adapter would likely filter out noise and transients to protect the GPS power supply against damage and be first to fail before the GPS unit IF the failure was associated with ybe GPS power supply, you did not specify the failure mode. The Model T is a very harsh EMI environment. The GPS is a high gain receiver with front end that may be vulernable to damage to receiver sensitivity (ie powers on and display is normal but may not receive enough satellites or no satellites at all to function).

[Oldav8tor]

I woke up in the middle of the night and it dawned on me that there must be a tester for USB charger/adapters....sure enough, $9 from Amazon. Duh....

The two GPS units worked great until they didn't. I also wondered how they would behave in the Model T environment with all the electrical noise but was pleasantly surprised. I never saw any sign of degraded performance. I hid a strip of velcro below the windshield to attach the GPS so I can remove and hide it in seconds for a more authentic look.

I used ten year old Garmin Nuvi units that I bought cheap on ebay. Both GPS units are profoundly dead.... I don't know if the failure of either was preceded by a problem with the adapter. I'll be checking the adapters when the tester arrives.

Any suggestion as to a type and value of a capacitor to put across the +/- terminals on the back of the adapter? I don't think it would hurt.

[TXGOAT2]

My Garmin does not seem to suffer from EMI, but my car has a metal firewall and a metal coil box out under the hood, which may help a little. As an experiment, I fired up the car and took an old, non-PLL multiband portable radio out and tried the AM band. As expected, in or near the car, interference was heavy, although a couple of low power local staions about 20 miles distant could be heard. The interference did not sound like 4 cylinder ignition noise. I turn on the headlights to load down the generator, and the strong interference almost disappeard, allowing loud and clear reception of AM stations over 120 miles away, with some low background popping from the ignition. Shortwave from 4 to 12 MHZ was clear, as was CB at round 27 MHZ. FM 88-108 MHZ was crystal clear, and several higher bands were also clear. This particular radio is a 30-40 year old portable in a cardboard case. The AM antenna is evidently one of the ferrite core directional types, which makes using it in the car inconvenient, regardless of interference. The FM high band mast antenna sufficed for strong FM reception in this far-fringe area. To sum up, the main source of interference in my particular car is the generator, at least with a radio that has an internal power source. I suspect that a good auto AM-FM radio with the antenna mounted toward the rear of the car would work pretty well in this car, if it ran on its own battery and if the generator had a filter of some sort to keep the AM interference in check. Whether any of this would apply to the Garmin receiver, I don't know, but the the radiated RF seemed to fall off very rapidly as I switched above the USA broadcast band, .55 to about 1.75 MHZ. Opening the hood of the car made no appreciable differance in the AM band interference. I would expect that an earlier car with a coil box inside the car and long plug leads would be a much noisier environment, as would a car with a wooden firewall, coil box, etc.

[TRDxB2]

Frank
I suspected the first USB adapter and replaced it with one designed for 12-24 volt marine use. I’d like to test it but need to figure out how to connect to the + lead in the USB connector or cable. My electronic education dates to the vacuum tube era so I’m not up on the latest stuff. I used to build radios… now I’m lucky if I can operate them.

Have you tried resetting the Nuvi device (what models are they) you may be looking under the wrong rock.
With the Model T off, and the USB connected to the battery & GPS turn it on by holding the power button for 12 seconds to see it it will reset. (from Garmin support https://www8.garmin.com/manuals/webhelp ... CAE1F.html )
Also some older Nuvi's did not come with lifetime maps - not sure what you have

NOTE: from GARMIN
A product’s “useful life” means the period during which the product (a) has sufficient memory capacity and other required technical capabilities to utilize current map data and (b) is capable of operating as intended without major repairs. A product will be deemed to be out of service and its useful life to be ended if no updates have been downloaded for such product for a period of 24 months or more. Unless otherwise stated, the updates you receive under the subscription will be updates to the same geographic area included with your Garmin product when originally purchased. In some instances, your Garmin product might not have sufficient memory remaining for you to load an update to the map data, in which case you will need to either (a) select reduced map data coverage for your updates, or (b) purchase separately a microSD™/SD™ card (if and as applicable to your Garmin product) and load all or a portion of the map data coverage for your updates to the card and insert the card into the microSD/SD card slot contained in your Garmin product. If neither of the measures in (a) or (b) can be used to address your product’s lack of sufficient remaining memory, then Garmin may conclude that the “useful life” of your product has expired. Garmin may terminate your nüMaps Lifetime or other lifetime map subscription at any time if you violate any of the terms of this agreement or your subscription. Your nüMaps Lifetime subscription or other lifetime map subscription may not be transferred to another person or another Garmin product

[Luke]

Tim,

It may be coincidental that those units have failed, given their age, however I run a number of such older (Garmin) units in vehicles I have here and they're all still working fine. Thus I'm inclined to agree that you should thoroughly check out your electrical system.

Your USB tester will almost certainly not tell the whole story if you have voltage spikes or feed problems that are somehow damaging your GPS units. Probably the most common and effective means of determining if that's an issue would be an oscilloscope, so if you could find someone that has one and prevail upon them to assist I suggest that'd be a good idea.

Otherwise I'd very closely inspect and clean all the electrical connections in your car, and only plug in the GPS when the vehicle is running.

As you'll recall from flying we always have the avionics off when starting a 'plane (esp with an electrically driven starter motor). A significant reason for this is the massive spikes that can occur due to high current draw/back emf that can damage sensitive electronic gear. Your T + GPS is no less susceptible to this, in fact probably more so especially if the electrical system is old and/or in poor condition. An example of this enhanced risk is a simple dirty connection that could be rectifying some of the EMI that Mike's mentioned which in turn could introduce quite high voltages into your unit.

Modern vehicles will generally do a disconnect of sensitive gear automatically upon start, and/or have suitable crowbar systems in place to protect the electronics, but the dear ol' T doesn't, so it'll rely upon you to do this. As for having the equipment connected while charging - no, not a good idea, especially if you have any poor connections I mentioned...

Luke.

[TXGOAT2]

I've been unplugging my Garmin whenever I leave the car, not because I was aware of any risk to it, but because the cigarette lighter adapter plug that powers it has an LED pilot light that stays lit with the device off. It also feels heavier than a simple plug ought to, so I assume it has some sort of power supply in it. I'd like to shorten the power supply cord, but I don't know if it's a simple cord or some sort of shielded cable, so I've left it alone. Based on the LED light in the plug, I assume it might draw some power, so I turn off the Garmin and unplug the adapter whenever I leave the car. I always push the car out of the metal barn, then start it, then plug in and turn on the Garmin. The battery charger requires unplugging the Garmin supply socket to charge the 12 V battery, so I don't have to remember to do that.

[Art M]

I power my garmin with the 6 volt car electrical power. Ot works well. Very little draw

Art Mirtes

[Art M]

I leave the garmin on while stopped duringz tour

[Oldav8tor]

Great info! Some comments: (1) I'll see if it wants to reset. That would certainly be a good outcome. (2) I use a key switch which does not apply voltage to the auxiliary circuits while cranking. My starter is a 12 volt WOSP unit. My car didn't come with an electrical system so what I have is of my own design. (3) I might know someone with a working oscilloscope.... I'll ask around. (4) the GPS units are 50LM's which come with lifetime maps. I added a micro SD card as the internal memory was maxed out and could not accept more recent updates. With the SD card the update went smoothly.

I appreciate your comments and suggestions....you've given me a few things to think about and investigate.

[TRDxB2]

Great info! Some comments: (1) I'll see if it wants to reset. That would certainly be a good outcome. (2) I use a key switch which does not apply voltage to the auxiliary circuits while cranking. My starter is a 12 volt WOSP unit. My car didn't come with an electrical system so what I have is of my own design. (3) I might know someone with a working oscilloscope.... I'll ask around. (4) the GPS units are 50LM's which come with lifetime maps. I added a micro SD card as the internal memory was maxed out and could not accept more recent updates. With the SD card the update went smoothly.

I appreciate your comments and suggestions....you've given me a few things to think about and investigate.

Well now.... Learned a few things about my Nuvi investigating yours that I didn't think about: 1. there is a fuse & 2. it has a battery (yeah! what was I thinking). The battery is likely the issue. When its plugged in your just charging it, when you turn the vehicle off it asks if you want it to stay on. The unit is 10 years old about the life of a lithium battery
The following PDF is the owners manual for NUVI model's prefixed 30, 40 & 50 it may be that some things don't apply

nuvi_30_40_50_EN_OM.pdf

(832.99 KiB) Downloaded 75 times

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These instructions are for the fuse - I haven't looked at mine to see if it applies

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Battery swap instructions

How to swap the battery

Battery swap inst.pdf

(1.85 MiB) Downloaded 76 times

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The battery is a Garmin 361-00056-00 there are many seller's but need to make sure the replacement is "new". I'd get one from BatteriesPlus, price is about the same and they may even replace it for you for free, & if it doesn't work for them then you know the GPS is dead

[Luke]

Frank,

That's useful information. For some reason I thought Tim had determined the unit was destroyed but if he's not checked the inline fuse it'd certainly be worth doing that - although if that made it operate again all the comments around why the issue might be occurring remain valid.

Tim (or perhaps anyone who isn't Tim and has a Garmin GPS without 'LM'!), it's relatively straightforward to produce your own up-to-date maps for the Garmin from current Openstreetmap data. Thus if you have an old Garmin languishing in a drawer somewhere it could be worth getting it out and making use of osmctools/mkgmap/splitter in order to get it current.

Luke.

[Oldav8tor]

More great info. My comments: (1) I don't use the Garmin power cable with the integral fuse. Instead, I purchased a short USB power cable which I plug into a USB adapter. The adapter has integral over-load, over-current and Short Circuit Protection

(2) If you think a dead battery might cause the whole unit to fail even when connected to external power, it would be worth checking out. Before spending $ on a battery (that may not be the solution) I might try swapping in a battery from a unit that is still functioning. I have a Nuvi 40LM and three 50LM's. Two of the 50's still work but their battery life is limited. I'll need to track down a T-4 Torx to remove the corner screws.