12v to 12 volt inverter

[Tony]

I have seen his 12v to 12v inverter from Maplins. Would it be suitable to fit this into a made up extenion lead for use from my positive earth cigar lighter. Hopefully this will allow me to use my Sat Nav which is a negative earth device.

http://www.maplin.co.uk/1w-single-outpu ... tors-98174

[christopher storey]

Tony : You might consider reversing the polarity and changing to negative earth . There are others here who are better versed in it, but basically it involves reversing the battery connections and then "flashing" the dynamo to reverse its polarity. It's a very long time since I have done it, so I will not attempt to give detailed instructions, but i am sure someone else will give them. The problem is if you have any polarity sensitive apparatus such as a radio

Edit : here is one set of instructions

First you need to disconnect any radio that you may have as this is going to be the wrong polarity as is any electrical clock.
Remove the coil connections ( you might need a new one but not often)
If you have an Amp meter this will need changing over later so remember this.
Now disconnect your battery and your dynamo but not the regulator.
you need to ensure that both the D and the F terminals are not connected to any cables.
1.With the ignition off change the battery connections over, you will need to change the terminals on the cables as they are different sizes too.
2. With a spare length of cable run a wire from the +ive terminal ( now non earth) to the dynamo. but dont connect it yet.
3. Ensure you have removed all polarity sensative equipment from the vehicles electrics.
4 take the end of the wire from the battery and "FLASH" the end onto the F terminal of the dynamo, Do this a couple of times and you will see a bright spark, this is normal. You have now changed the polarity of the dynamo.
5. Disconnect the earth of the battery reconnect the D anf F terminals to their respective connectors and check they are still on the regulator. Check the wiring of the coil as B will now be +ive to the battery and C will be -IVE to the breaker points.
6. reconnect battery and try ignition switch be ready to turn off if a problem.
7.Swap the +ive and -ive of the clock (check with a volt meter) and check the polarity of the Amp meter
8. your +ive earth radio is now of no use and you can sell it on Ebay, buy a modern ICE for your pleasure.
9. Check the wiring of your cigarette lighter socket as this will now be reversed and any items you had used before might need their polarity checking or changing.
Be prepared to replace fuses as there are bound to be some items you've forgotten to reverse

[Heuer]

Tony

As you will be leaving for France fairly shortly I would suggest doing anything major to the car would probably not be a good idea. If you want to get your SatNav working then install a cigar lighter in the glove box. As the glove box is non conductive fibre you can switch the connections around, +ve to the centre pin, -ve to the casing. Cost is about ?27 from SNG plus about 30 minutes of your time: http://etypeuk.com/forum/viewtopic.php?t=168

We use this for our SatNav as it keeps the cables away from the dash because they get in the way when changing gear or reaching for switches. Invariably you will knock the plug out of the socket at the exact moment you need travel guidance. The cigar sockets are not really designed to hold the large plugs and substantial wiring of these devices so even if you do get the inverter to work (check the consumption on the SatNav as the Maplin one is only 1 watt) or change the entire earthing of the car using the central lighter socket is impractical.

[wagstefan]

ALTERNATIVE: As polarity is always a matter of level, there are some sealed voltage doubler on the market. You will find them on Ebay.

Simply double the plus from the battery or body to receive +24V and then you could connect modern SAT-NAVS or modern radio with grounding it at the body (minus goes to body as you would do with special "plus on body" compatible gadgets. And the doubled voltage will connect to plus at the SAT NAV). So you will finally have +24V against +12V resulting in +12V against the body voltage level.

I hope this helps!

Good luck and best regards

Stefan

[Tony]

Stefen, Could you point me to one of these sealed voltage doublers on e-bay.
It could be just the terminology used but are these the same as inverters. etc

[Tony]

Well I have decided on David's advise regarding not risking a positive to negative earth conversion so near my main holidays , plus I would have to buy a new radio. I have taken Sefan's advise about a converter (Sealed voltage doubler) and bought this from Ray Smith.

http://www.raysmith.co.uk/positive-earth-adaptors.html

Now is the time to tell me if I have bought the wrong thing and wasted ?70.

The risk of just swapping over the wire without a fully insulated adapter is. that if I ever did earth the devise to the body I could blow it.

I believe these inverters use a small amount of power even when not in use, so I may stick a switch in the line to be able to isolate it. Any ideas where I can take the supply off from behind the drop down instrument panel. Would the supply off back of cigar lighter be a good option as I will never use it. I could run a supply from this to a USB port in the glove box as per David suggestion. Or would the ignition switch be a better option as it would save me putting in an in-line switch.

So come on you budding Auto Electricians, before I burn my car down.

[wagstefan]

Hi Tony,

I have this one on my watch list: http://cgi.ebay.de/ws/eBayISAPI.dll?Vie ... K:MEWAX:IT

But looking firstly now at your first link, I assume that the inverter N85DC (12V to 24V) might have done it as well. Maybe the power is too low so that you would have needed to put some in parallel.

Now as you have acted already (sorry for my late reply - I am currently in the USA) and looking at your purchased product, I think this is the very best choice! It might be a bit more expensive, but its operation is guaranteed (it only purpose is to do as supposed and desired by you), it is isolated, it brings the right power output, it is secured against polarity overload and short circuit. And if something goes wrong you could go back to the vendor.

So for installation simply follow the instruction in the description. And measure the output against ground (must be approx. +12V without engine running and +14V with) before connecting something. And I would recommend to connect to the ignition switch unless you plan to operate the SAT NAV or radio often without the engine running?!

I am not sure, what you meant with a USB connect in the glove box? Are you planning to provide power to the SAT NAV through USB (only)?

Whatever I think you did the absolute right thing and I am a bit jealous as I have not performed such a conversion. But I was investigating a lot and found this methode and am planning to do so in my 63' FHC. When it comes to it I might also take the one you have ordered! My 61' FHC will stay on an old Becker Europa (operting on plus on body) only extended by a connect for an Ipod.

But only heaven knows, when my cars will finally be ready.......

Good luck and keep us posted on the success and your experiences.


Thanks!

Stefan

[Heuer]

Seems to me you are playing a dangerous game of consequences here - inverter>risk of flat battery>isolating switch>risk of earthing>USB connector>voltage reducer etc. Too many points of failure. Back to basics:

1. Most modern Sat Nav devices (and iPods's, Phone's etc) require a 5 volt supply and the cases are isolated.



2. To power these devices from a 12v car system the voltage is stepped down to 5v using the ubiquitous cigar adapter plug modified to suit. These are either hard wired into a mini USB connector, bespoke phone connector (e.g. iPhone) or a cigar plug with a USB socket at the end for use with a standard cable:



3. For a +ve earth car you need to do one of the following:

a) use a secondary cigar lighter isolated from the chassis and connect 12v +ve to the centre pin and -ve to the casing - this is what I did, see my post.

b) take a cigar plug connector for your device and swap over the red and black cables inside the plug (easier than doing the USB end) but you can never use it in a modern car.

c) disassemble a spare cigar adapter, hard wire to the car, conceal under dash and either run a USB fly lead for your device or connect to a USB socket in the glove box or dash.

4. If you have something like a Garmin Nuvi (like mine) with traffic updates you must use their supplied adapter plug/cable although you could modify the internal wiring PROVIDING you don't use it in a modern car. Consequences again!

5. You still need to consider where to plug the SatNav in:



As you can see if you use the central socket you will keep knocking it as you change gear (it will eventually break!) and it obstructs your use of controls and dials.

Seems to me you are looking for the most complex solution to a very simple problem, and try explaining it to a French garage mechanic armed only with an E-Type Service Manual (you will be taking one I hope) if you have unrelated problems. For reliable touring avoid any electronics and Keep It Stupid Simple!

[wagstefan]

Hi David,

Sorry, may I slightly disagree in regard of the risk of earthing / isolating switch and the fact, that this is a dangerous game at all? Also the point with a flat battery can be overcome if you take "minus / not earth" from the ignition switch being not sure, if this inverter really could flatten the battery when being connected differently.

This inverter has to be seen like a normal electric consumer. So your "minus / not earth" goes into the inverter as it would be into a radio, the windscreen washer pump, the ventilation, etc. at a plus on earth car. And you can and even must earth the inverter, so there is no issue at all if the item gets in contact with any earth (in this case minus).
Therefore it is not at all more risky than having any other electric consumer connected. I would rather claim that your change in polarity at the additional cigar lighter might be risky as the housing must not be in contact with any "plus / earth".

But believing you did a thorough isolation this solution might be as good as the inverter one. However the real advantage, the one, which makes it the best and easiest solution is, that you can use a normal "minus on earth" consumer like a radio, earth it on a "plus on earth" car and simply connect the 24V output to the "plus input" on the radio. So you can install every consumer as usual, earth it as usual and you do not need to take care of a fancy isolation of the body of e.g. the radio, which you normally would have needed to when just changing the polarity.
For SAT NAVs this might not be required as they are not earthed at all. Sorry, I have not had this fact in mind anymore. However still believing that the inverter solution is the best one.

In addition please find under the link much more detailed information on the topic and funnywise when searching for the link I found, that the same inverter was recommended!

http://www.mgaguru.com/mgtech/electric/et207.htm


Thanks

Stefan

[Heuer]

I fully agree your approach will work Stefan but if you are going to that much trouble why not do as Christopher suggests and change the polarity of the whole vehicle? I doubt even a concourse judge would be able to spot you had made the changeover providing you did not fit the '-ve earth' plate on the heater. As Tony is about to embark on a 3,000 mile tour of France and his only requirement, apart from reliability, is to operate a SatNav the addition of complex parts is not to be recommended in my view. It would be better to install the inverter on his return and run the car in the UK for 9 months until his next trip. This means he will be fully aware of the various dependencies (e.g. will it really run the battery down if not isolated, how much heat is generated?) to help with diagnostics if there is a problem.

I also notice the author of that link you provided says: "The only people who should even think about installing a negative earth device in a positive earth vehicle should be devout members of the Positive Earth Society who insist on keeping the car's electrical system wired as positive earth for concours reasons, while installing some negative earth electronic device(s), which wouldn't be concours anyway. Anyone else should just convert the car to negative earth."

Actually my concern with that inverter is how hot it will get having been operating all day in an already hot confined space (behind an E-Type dash next to the bulkhead) with ambient temperatures of 35c+.

[Tony]

Thanks for the reply' s guys. It seems to have started a healthy debate.

The reason I went for the invert was to eliminate the risk of accidentally earthing the devise I have plugged in, although devises seems to be well insulated these days. I take David's point about using a cigar lighter socket with a USB adapted plugged in to bring the volts down to 5v. So I will go that way.

As I think the theory goes the inverter takes volts up to 24v , but by connecting it back to earth (neutral) the volts come back down to 12 volts. again. The USB adapter in the cigar lighter bringing it down to 5volt.

The issues now is the inverter getting too hot while the engine or ignition is turned on. I will keep a close eye on this before going away and try and place it in a fully accessible well ventilated position well away from wires or combustible material.
I suppose as it is only for the holiday period I could get my wife to hold it up above her head. I will report back on the heat situation.

I an now going to read Stefan's post again to understand the different between neutral and earth.

I think i can smell burning, have to go

[Heuer]

Tony

1. All SatNav's and phone cases are isolated from the power lines so no need to worry. The inverter is simple in operation although the theory does play with your mind. Think of it this way - your battery is 12" high, the inverter is 24" high; the distance between the top of the battery and the top of the inverter is ........... 12". Think the same way when it comes to electricity, the output of the inverter is 24 volts so 12 volts above the 12 volts of the car battery.

2. What make and model of SatNav are you using because I can then tell you whether the current drain will be sufficient to generate excess heat? The inverter you have will dissipate 50 watts under full load. My Garmin Nuvi draws 2 amps so when connected to the inverter there would be about 20 watts.

3. Bit concerned about you using one of those after market cigar plug USB adapters as some are rated at 100ma , others at 1 amp - OK to charge a mobile but neither would be good enough for a SatNav. Suggest you use whatever was supplied with the device.

[Tony]

Well the inverter is in and giving out 12volts without burning the car down so far. I now have to give it a good test to see how hot it gets under load.

I will report back on progress. As stated before I have put a switch in the supply line so I can turn off the inverter when not is use.