Transistor wiring question - Caravan 12V circuit

Thread Starter

aaronpricey

Joined Feb 9, 2020
7
Hi There,
I have a question about Transistor.
i understand the basics of how they operate however i have recently purchased a 2nd hand caravan and wanted to get my head around the 12V DC circuit. i noted that the transistor is wired in a way which was unfamiliar to me.

you will see from my hand sketch of the 12V system how the transister is wired. please note i took the labeling of base collector and emitter from the texta markings under the transistor (which also i think may be wrong??).

the markings on the transistor are faded off so cannot get a type off it.
the Anderson plug connects to my car which is connected to the alternator (which is suppose to charge the Caravan Battery)

i'm hoping somebody may be able to help shed some light and tell me if this wiring is ok (to me it is not) and what the circuit may be doing.

thanks
AaronCaravan - Circuit Diagram.JPGCaravan Power Board.JPG
 

paulktreg

Joined Jun 2, 2008
799
I see no reason to wire a transistor in this way unless its supposed to behave like two parallel oppositely wired diodes?
 

BillB3857

Joined Feb 28, 2009
2,543
As the transistor is drawn, power would be supplied to the anderson plug from the caravan battery. Are you sure that the transistor is an NPN type and not a PNP type? If it were a PNP, it would allow the automobile to provide some charge current to the caravan battery and any load the caravan may have connected. It is also possible that the device you see as a transistor is a TO220 dual diode..1581290219826.png
 

Reloadron

Joined Jan 15, 2015
5,900
Would this be the component lower right corner of the picture? Since you mention the writing on it is not legible how do we kow it's a transistor? Plenty of other devices come in a TO-220-3 package.

Ron
 

Thread Starter

aaronpricey

Joined Feb 9, 2020
7
Thanks for the reply's. Much appreciated.
yes it is the component on the lower right.
it was an assumption that it was a transistor due to the appearance and also the permanent marker under the terminals states C & B, so assumed Collector & Base. I will get a picture of it and post.
Did not think of a TO220 dual diode.

with anderson plugs wired to the vehicle battery & the van in tow with the internal fridge running on 12V. when stopped for long periods of time people disconnect the anderson plug so the fridge does not drain the vehicle battery.
maybe it is wired to assist this?

- two parallel oppositely wired diodes? interesting i will have to research how these function.
 

AlbertHall

Joined Jun 4, 2014
11,164
Probably that is the two diodes in parallel (to handle the current) and they would stop the battery discharging into whatever it connects to in the car while allowing the car to charge the battery.
 

Rich2

Joined Mar 3, 2014
179
Probably that is the two diodes in parallel (to handle the current) and they would stop the battery discharging into whatever it connects to in the car while allowing the car to charge the battery.
I thought that but why would anything be switched on in the car without the engine on? And if the car battery went flat it would be handy to charge it with the caravan battery/charger anyway.
 

Thread Starter

aaronpricey

Joined Feb 9, 2020
7
I thought that but why would anything be switched on in the car without the engine on? And if the car battery went flat it would be handy to charge it with the caravan battery/charger anyway.
would this all depend on which way the diodes are biased?

if they forward bias to allow current flow from car to caravan, then there is nothing to stop the car battery discharging.
if they are forward bias to allow current to flow from caravan to car, then is doesn't seem right and on long trips the battery in the caravan would not be getting charged from the alternator.

So I will disconnect the component and try a diode test on it.

Maybe it is to prevent the caravans internal battery charger (mains powered) from charging or damaging the car battery?
 

Rich2

Joined Mar 3, 2014
179
The car is disconnected on site anyway. Also the fridge and reversing light supply is usually either in another 7 pin white round socket or a more modern 13? pin socket. Are you sure the Anderson connector is for the car?
 

Thread Starter

aaronpricey

Joined Feb 9, 2020
7
The car is disconnected on site anyway. Also the fridge and reversing light supply is usually either in another 7 pin white round socket or a more modern 13? pin socket. Are you sure the Anderson connector is for the car?
i only have a 7 pin plug and the Aux power / reversing light pin is wired to charge to "break away" battery (only a small gauge wire) the guy i bought it off told me it was to charge the battery from the car? Maybe it is for Solar Panels?
Although the cable and plug run along side the trailer 7 pin plug as though it should go to the car?
 
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