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MG TD TF 1500 - Wiring the TF for a USB phone charger

On a recent trip, I noted towards the end of the day the phone battery was getting low. We did stop at a Starbucks for coffee and charged the phones while we were there. So...I'm looking to put in a small out of the way 12 V USB. Given I'm running positive earth, any issues or considerations when doing the wiring?

Thanks,

Jim
Jim Rice

I have two cigarette lighter type ports on my TF (also positive ground). One for phone charging and the other for a Tom Tom. They are both a full plastic housing that I set into a piece of walnut under the dash. Maybe not the mpst attractive but it has gotten the job done for me in my cross country travels. You can find them at Boat dealers and probably parts stores.





L E D LaVerne

I did basically the same thing as LED did except that I mounted my accessory outlet out of sight up under the dash on the passenger side. Just wire the center lug to earth (+) and the side lug to power (-) and be sure to use an insulated accessory outlet and double insulate it from any metal. Boat supplies are probably your best source for the outlet.

Jud
J K Chapin

I added a plate to the H shaped brace under the dash, has a lighter socket for GPS and dual USB socket for phone, switch to select which fuel pump is used.

Fuse anything you add, 5Amps works for phone or GPS. I took power off the A4 fuse so the sockets are switched by ignition.

EBay has plastic sockets so safe with positive earth although converting to negative earth takes less than 5 minutes.

Peter
P G Gilvarry

I added charging ports to my MGA for the same reason. There should be no problem with positive earth if the ports are insulated from the chassis. One thing to remember, however - If you are using a "cigarette lighter" port, its ok to use a constant voltage source to allow for charging without the engine running. If using an actual USB port, these are electronic devices and constantly draw from the battery, even if not charging anything. Be sure to use a "switched ignition" source.
Bruns

Thanks all for the input. I did buy a dual USB port unit as opposed to the cigarette lighter port. It's housed in plastic/nylon casing, has it's own on/off switch, and I plan to mount it inside the passenger glove box on the rear wall which I had fabricated out of ABS plastic sheeting. So isolating it from any metal should not be an issue, and plenty of open space behind the glove box as well. That's the easy part.

I'm not electrically inclined so I'm not sure of the electrical connections that follow. The actual sealed unit has the + and - connections protruding out the backside, and comes with two loose wires (red/black) with the red being fused (10A). Do I simply connect the positive connection on the unit to ground (using the red wire) and the negative connection to power (using the black wire)? I do plan to change the fuse to a 5A, but does it matter which wire that fuse is actually on?

I'm thinking about not using a switched ignition power source since the unit has it's own power on/off button, and I may want to be able to charge the phones without having the ignition on or engine running. Having the ignition on energizes a number of components including the fuel pump. A4 is switched. What about A1-A3?

Thanks, Jim
Jim Rice

Jim, you've got it right for a Pos. earth car. Red (+) to any convenient ground. Black to any convenient Negative (-)(Hot)(from the battery) source. Other's will tell you which lug on your regulator is switched and which is not. I think it's A and A1 but it is easy to tell with a volt meter. Just set it on the 15v. scale, put the + lead (usually red) to earth and, with the switch off, using the black lead see which lug has voltage.

I strongly recommend putting an in-line fuse in the hot (black) wire.

Jud
J K Chapin

Jud:

A1 & A2 are un-switched. I checked with a voltmeter. Of course if I had checked the WSM first, it clearly notes on page N.15 that A3 & A4 are switched and A1 & A2 are not. I'm looking at using un-switched power mainly knowing how much my better half uses her phone especially when we're attending car shows. Usually those last 6 hours or more. So about halfway through, her phone starts displaying "low battery". This way we can plug in the phones without having the ignition on for extended times. I surmise we might use more power energizing the car's electrical system with the ignition on than we'd use to charge the phones with un-switched power.
Jim Rice

The dual USB port will draw power even if there is no phone plugged in.

Your battery will suffer, unless you disconnect the battery when you arrive and reconnect to charge the phone.

Peter
P G Gilvarry

Also, I don't think TDs have an "Accessory" position in the ignition switch so if you did use a switched source, you'd be most likely energizing the coil which would waste energy and could cause problems.

Peter is right about the charger but if you just get an insert with two USB ports that goes into the accessory socket, you can remove it when it's not in use and that will stop the electricity drain.

Jud
J K Chapin

Peter:

If the marketing claims are correct and the user reviews are truthful, when the on/off power button is pressed, it's supposed to kill the unit. I suppose I can validate that by seeing if the phone is registering any charge with the unit turned off and the phone plugged in. That said, I guess it's possible there may still be a parasitic power draw by the unit itself that isn't controlled by the on/off button. I don't know if there is a way to test for that possibility or not. Is there a way to perhaps use a multi-meter across the battery terminals or a different connection point to detect any such power draw? When not driving and parked at home, the battery is hooked to a trickle charger. I guess the concern would be if on a trip and not having a trickle charger, and assuming it does draw power, could the unit drain the battery overnight? Seems it would need to draw a lot of power when not in use to discharge the car battery in short order.

Jim







Jim Rice

Jim, I've never seen a device like that but it does look perfect for our +earth cars. May I ask where you got it?

Are the terminals on the bottom marked for Pos. and Neg.? If not, are they marked for the red and black leads? If the latter one must assume that the red goes to positive and the black to negative.

Were it I, I would temporarily hook it directly to a battery with an ammeter on the red side and measure the current draw (1) switched off with nothing in the ports, (2) switched on with nothing in the ports and (3) switched on with a phone charging from one of the ports.

In the first two cases you should get 0 current draw but, as Peter said, there is probably some draw through the device (switch on, test 2) even when nothing is plugged in. In the third case you should get a current draw in the range of 1 to 3 amps. Solid state devices don't easily follow Ohms law but an output of 3 amps at 5 volts is 15 watts. Twelve volts will give you 15 watts with a current of 1.25 amps. Adding a fudge factor for system inefficiencies I would expect a reading on the ammeter of not more than 1.5 amps when charging one phone.

If you decide to run these experiments, please let us know your results.

Thanks.

Jud
J K Chapin

Jud:

See attached link:

https://www.amazon.com/Charge-Charger-Socket-Waterproof-Motorcycle/dp/B082PNLMDS

Jim
Jim Rice

Jim,

I have never see one with an on/off button, with it off you may get no current draw.

I had a Nissan truck with a lighter socket that was always live. I left it with a phone charger plugged in while I was away overseas. When I returned the battery was flat.

It is the circuitry that converts the nominal 12v to the USB that draws current continuously. Hopefully with the switch that will not happen.

Peter
P G Gilvarry

Well, I didn't look carefully. The "3.0" refers, I think, to the USB standard, not to the max amperage output as I thought. At full load (36 watts per the literature) and 5 volts the current draw is 7+ amps plus system inefficiencies. For 12 volts to deliver 36 watts takes 3 amps so 3-4 amps should be the maximum draw from your car.

One reviewer said the switch only turns off the blue illuminating light but several others said it completely disconnected the device. For boats that spend a lot of time idle, the latter would be a desirable feature.

Looking forward to your results.

Jud
J K Chapin

Well...for $10 plus shipping it might be a crap-shoot as to how well it will work. It's being delivered today, so I can install over the next few days and then try to test what it actually does. I'm not sure I have an adequate ammeter to test the draw. Maybe if the unit is "turned-off" just to see if there is any parasitic power use. The multi meter I have is an old Sears analog type. It has two setting for mA DC: 25 & 250. I THINK if set on 250 mA, the max. amp equivalent is .25 amps. So, if the unit truly shuts off all power, then the reading should be Zero. If there is some small parasitic power use perhaps the multimeter can handle that without being damaged? Again...not being electrically inclined, I'm kinda guessing here.

Worse case I suppose would be to connect it to switched power, or install an in-line switch to truly cut power to the unit when not being used.
Jim Rice

UPDATE:

Well...the crap-shoot didn't pay off. The unit was defective right out of the box. To test, I connected it to the other cars battery (negative ground) and attached the wires accordingly. Unit did not turn on or light up, and would not charge the phone. Returning it for credit. maybe a cigarette style aux. port with a USB adapter is the more reliable method to use.
Jim Rice

Well, drat!! I decided to order one to do my own tests. I'll see if I have any better luck.

I hope you won't be offended but did you check that the fuse hadn't been damaged in transit?

Jud
J K Chapin

I did....twice. Also checked the leads connected to the battery (with the fuse installed) where they attached to the unit. There was power to the unit.

Jim
Jim Rice

There's a whole gaggle of these on AliExpress, some as low as >$5 incl shipping.

Have a look at :- https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20220611102552&origin=y&SearchText=USB+Outlet+QC3.0+Dual+USB+Power+Socket+&spm=a2g0o.detail.1000002.0

Gord Clark
Rockburn, Qué.
Gord Clark

Well...I didn't give up on the dedicated USB port. I did find a pretty rugged dual charger (model 1045) made by Blue Sea Systems. It was fairly pricy as it's intended for marine applications, and with a 4.8A charging capacity. It does not have an on/off button nor is it backlit. The standby power draw is only 1 mA. I talked with the engineer who designed it. Interesting conversation. Since I did hook it up to un-switched power (A1) as I intended, the almost negligible power draw was appealing to me. Used a 4 amp fuse on the power wire per his recommendation. Plugged in the phone (Samsung S21) and it charged quite fast! I did brace the back of the glove box with plywood (1/8 inch) attached to the flanges, so the charger is solidly anchored. For sake of transparency, I have no affiliation with this company.

Jud...how did your experience go with the other charger?

Jim






Jim Rice

Jim, I just got the charger yesterday. It's 96+F here so I haven't really had a chance to hook it up and take measurements but I'll do that soon.

Jud

ps: Your installation looks quite spiffy.
J K Chapin

Jud - thanks for the interesting thread. More particularly, I delight in seeing the word "spiffy" after all these years. Keep up the good work!
John.
J P Hall

Well, the threat of a thunderstorm cooled things off a few degrees (just noise but no rain which we disparately need) so I did some testing on the USB charger (see Jim's Amazon link above). My car is positive earth. I attached the red (+) wire from the braided ground strap to the positive post on the USB charger. I ran the black wire to one post of a 10 amp DC ammeter (I got the ammeter polarity wrong the first time and buried the needle so I simply reversed the connections to the ammeter) and the other post to the unswitched fuse below the voltage regulator (I was going to draw power from A1 but couldn't make an easy alligator clip connection there so I used the fuse). Next I plugged in a partially charged (63%) iPhone and a partially charged (??%) blue tooth speaker into the charger. I then played a half a dozen Simon and Garfield songs to, hopefully, place maximum load on the USB charger. When I finished the iPhone had charged from 63% to 85%.

Image 1 shows the current draw with the USB charger "on." Image 2 shows the current draw with the USB charger "off." I think the little bit of current in image 2 is just that I didn't carefully set the meter at zero before getting started.

In any event, it looks like max draw is about 0.4 amps and minimum is 0 - 0.1 amps. My car has a 200 amp-hour battery so I should be able to go about 400 hours before I deplete the car battery.

The charger seems satisfactory to me. I plan on building a new vinyl covered dashboard in the near future and I'll definitely incorporate this device into it.

Jud






J K Chapin

Jud:

Good to see the one you got works as advertised. Send a picture after you get it installed in your dashboard. Should look good with that faint blue glow.

Jim
Jim Rice

Will do.
J K Chapin

This thread was discussed between 30/05/2022 and 16/06/2022

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