Electrical Connections

I felt pretty stupid today. I went and bought a Hella type plug today to plug into my Waeco/Hella socket. When I started to take the original plug apart I realised you could just remove the red plastic bit for the same effect :-( live and learn.

Don't feel bad...I did exactly the same thing!

hahaha , you're both idiots then ;)

Actually , I only found out cause mine fell apart

Make that 3 idiot's, did the same myself....

Well, that place I bought my hand held spotlight from showed me that this type of plug worked like this, you need to go to a place with better service, or better still:

Jimbo send me your Waeco, I will test it for 12 months and then advise you completely on all its operating requirements

Moggs, Flappan and Paul can follow on a year by year rotation. I supply this service free of charge, of course transport costs for these appliances will be your responsibility.

Merry Christmas

How much beer should I send for you to be able to adequately conduct this Scientific Extravaganza?

I will provide refreshments, just fill the Waeco with money , which provides excellent insulation. I will make sure that it is gone by the time it is due for return and your report.

You're a "kind" man.

The 'kinda" man who should be shot.

Have a good Christmas Professor.

Cheers,

Jim.

Peter 2,

I second that statement, a fridge should have a dedicated power supply direct to the battery.

The fact is;
a cigarette lighter plug, in most instances is not rated to carry the required power needed by the fridge at startup, whether it is waeco, Engel etc is not relevant, and also cause voltage drop due to ineficient connection.

Mainey..

Mainey,

Have you measured the current draw of these fridges at startup ?

Mad Dog (Vic)
No, I have not personally measured the current draw of this fridge at startup, however I know it to be common factual electrical knowledge and it can also be read on the Danfoss website.

All electrical fridge motors, when they start, initially have a larger current draw, with only one exemption that I am aware of, and that one will not be on the market till Feb 2005.

ok, I thought you may have done some measurements. Engel state that the swing motor they use doesn't have a large start up draw because the swing compressor starts with a small stroke and slowly builds up to the full swing. I haven't got to it yet but I'll tqke it to work and put it on a scope to check their claims.

Again these forums are the source of misinformation.

Mainey has stated:
The fact is;
a cigarette lighter plug, in most instances is not rated to carry the required power needed by the fridge at startup, whether it is waeco, Engel etc is not relevant, and also cause voltage drop due to ineficient connection.

The above is a statement but it is not a fact.

Don't get me wrong I love these forums and they are a great help to a good many people but I have a small issue particularly with the amount of electrical advice given that is factually incorrect, and potentially causes people to spend money which is ultimately wasted.

I recognise that those giving the information are trying to help and that that is admirable but if you don't know what you are talking about it isn't much help.

That said here goes (without too many techy terms):

Power is not carried it is generated or lost as heat. Current flows (could be refered to in laymans terms as being carried) and is measured in amps. The carrying of the current through the resistance offered by poor quality contacts and length of cable causes voltage to be dropped (sometimes referred to as lost at the point at which it is ultimately being connected to something.) The voltage is lost as heat and the loss can be calculated as a power figure. The power figure will give the amount of heat created in watts.

Some facts.

An Engel 40 litre fridge running in the back of a dual cab ute & supplied by 4mm cable from the engine bay via the following:
1. crimp connector and battery terminal
2. 20A fuse (fusing all power to cargo area)
3. 4mm o/d cable
4. Narva/Hella socket/plug junction
5. adaptor to OEM Engel cigarette lighter plug which contains a TCO or thermal cut out which can be seen in the fuse body with the arrow on it.

measured as follows:
Voltage at socket prior to turning fridge on: ~12.57v
Voltage at socket fridge running: ~12.05v
Min voltage at start load: 11.78v (average of 5 starts)
Fridge peak current at start up: 4.12A (average of 5 starts)
Fridge running current averaged for 3 minutes: 2.19A
Under normal running conditions described above the voltage drop from the back of the cigarette lighter socket to the blades on the back of the OEM Engel plug on average for 1 min 89.3 millivolts or 0.0893 volts.

(All measurements carried out using Fluke 87 DMM and Isotech DMM, both with max/min/avg capability. Current measured on Fluke & Voltage measured on Isotech with exception of the last voltage in millivolts which was measured on the Fluke 87)

From the above it is clear that
a) A cigarette lighter plug is more than adequate to carry the current required for startup and running a 40l Engel. (Logically if it wasn't Engel who sell thousands of these wouldn't sell them with one on the end of the lead would they? Think of the warranty problems it would generate!)

Further to that all of Narva's cigarette lighter products are rated at 10A with only a couple at 5A continuous. A product rated for these currents continuously can sustain much higher currents (with a proportional loss of voltage for short periods eg. A 100A isolator switch can handle 1000A for less than 10 seconds)

50A Anderson connectors are way OTT. If your Engel needs the capability to draw 250Amps at startup it's much bigger than mine.

b) More voltage is lost across the length of the 4mm cable (0.5v) than across the cigarette lighter plug/socket and Thermal cut out (TCO) (<0.1v). What's more the loss is more likely to be in the junctions than in the TCO which has roughly the same resistance as a piece of 18 gauge piece of wire ie. very low.

In conclusion, using anything other than the original cigarette lighter plug is not required, though to prevent the problem of it eventually vibrating loose over corrugations I will be changing mine to a fused Hella connector (part 4952 from memory) which should still allow use of the Engel thermal fuse, it hasn't turned up at Burson's yet.

I have no problem with running one pair of supply wires to run fridge and lights in the cargo area. I don't believe a fridge necessarily needs a dedicated supply - provided that the total current draw of all likely simultaneously operated equipment is taken into account and appropriate cable is used. A pair should be used though rather than earthing the negative side to the bodywork.

4mm cable will run a fridge but not much more - even a Versalight may struggle to turn on when the fridge has been running for a while.

6mm is far better as a 50% increase in diameter increases the conductor cross sectional area by 2.3 times with a dramatic reduction in voltage drop due to the lower resistance.

That said if you have a roll of 4mm-6mm cable lying around and want to run two feeds it's obviously going to be better than one. That way later if you want to plug in something unexpected in (eg. 100w spot pulling 12 Amps) you can do so. Just make sure you fuse them separately.

Sorry Mainey, no offence intended & I would hope none taken. I'd be happy to discuss it over a beer some time - my shout. You were right about the solder though.

Dave

Well said geocacher...
saved me the trouble, though I would have used less words (obviously don't type as quickly as you.)
A Danfoss compressor will run equally as well on the average Cig Lighter circuit.
A bigger wire is good- but not a necessity by any stretch of the imagination.
Cheers
And happy new year to all!

geocacher (djcache)

I posted (quote) a cigarette lighter plug, IN MOST INSTANCES is not rated to carry the required power needed by the fridge at start-up, whether it is Waeco, Engel etc is not relevant, and also cause voltage drop due to inefficient connection(end quote)

Dave,
Nope I’m not offended at all, and as I reread my post I don’t believe we are at different thoughts at all, as I believe the wiring behind the cigarette lighter is not 6 MM, as most will be using when installing a new dual battery system to run a fridge, if thin cable as is used in the cigarette lighter was ok it would be specified, and not 6mm as recommended by most qualified technical people, that is only my opinion and I am eager to see any replies not recommending 6mm but the thin wire as used in cigarette lighter cable.
Dave you state (quote) "6mm is far better as a 50% increase in diameter increases the conductor cross sectional area by 2.3 times with a dramatic reduction in voltage drop due to the lower resistance" (end quote)

After reading your post you do appear to state 6mm is the correct way to go... as I stated also.

Hi,

Part of the problem not yet stated here, is the shape of the connections inside the cig lighter.

Some of them have rounded ends on the plugs, some have flat. Same goes for the receptacles. How can you expect a decent electrical connection when a domed, rounded, plug is inserted into a connection that has a flat centre bit? We're relying on the electricity to be travelling through a tiny point where the things meet. Surely a recipe for voltage drop.

I've pulled apart several of the female ends and soldered a largish dob of solder onto the flat centre connection, then drilled it out with a 5/16 drill bit. This gives about the right profile for the rounded plug to seat properly and give a connection over a much wider area.

Now when I use a 5amp fridge in this plug, the plug is much much cooler which can only be a good thing.

Tim

Remember what the fag lighter was designed for, to take a fag lighter, huge contact area, only on for 30 secs (slow one) end of problem!!
They were never designed to take a plug and never designed to provide a permanent power connection.
Fag lighter sockets and usually the wiring behind them are useless in most vehicles, if you want a permanent power connection fit properly designed sockets and plugs to suit the current load, you will never look back.

You are right Peter but they did use a bit of current though - 10-15A.

The modification by Tim seems to be a lot of work to save $10 on a Hella style plug but would work quite well. If you look at the OEM Engel plug it has a flat end about 5-7mm in diameter at least and will adequately carry the current, and as is evidenced by the figures do it with minimal voltage drop between socket and fridge lead.

Mainey,

My issue was with your assertions that the cigarette plug - not the wiring - wouldn't carry the "power needed by the fridge at startup" due to an inefficient connection which is what you actually said.

The wiring behind the plug is a variable which is vehicle (OEM) or auto elec/aftermarket installer dependant and which you didn't discuss in your post UNLESS that is what you meant by dedicated supply and even then you didn't mention wire size at all.

Many people still need to be able to disconnect it to remove the fridge from the vehicle. Most people are always going to have a plug on their lead - all my mates do.

If you have two 4wds leaving the OEM lead in there isn't an option so being able to disconnect the lead requires a plug of some sort.

Your cigarette lighter socket in the dash is fused for 20A and the power only ones (not designed for a lighter) for 5A. Both will adequately run a 2A device and supply the very briefly required 4.2A startup current at an adequate voltage.

As I stated thicker is better when it comes to wiring, but it'll work with OEM wiring as long as you don't have the triple adaptor with the light and laptop or GPS plugged in there as well. The Engel runs just fine in the OEM socket in the back of the Forester when it isn't in the ute.

Hella plugs aren't optimal either but they are a better alternative to cig lighters. They lock positively and are rated to 20A which is well more than required but changing to those isn't a necessity.

Plugs and wiring are two completely different things which is why I discussed them separately.

I'm glad you agree with me but maybe what you thought you said was not interpreted as what was intended, and not just by me.

I wonder how many posts, some of mine included sometimes, mean one thing to those who write them and something completely different to many reading them. I'll bet it's worse with the ones typed in a hurry too.

Regards

Dave

nil? dont you mean 0.00nil voltage drop?

Merry Christmas

For joints that really matter I solder and fit a plastic covered brass screw on thingy over the joint. Solder gives the best electrical connection, and the screw on thingy gives mechanical strength.

Just a little bit more trivia Dave. The latest Ford GT doesn't have key start...yep push button.

The other thing is that voltage drop should be measured under load.