Bailey Unicorn 3 Battery Box

[PaulT]

The battery box on the series 3 Unicorns is in the middle of the floor, above the axle. We're always told, when fitting a mover, to keep the cable runs between the battery, the switch and the control box as short as possible. I presume that the on/off switch for the mover can still be fitted in the mains inlet box but has anyone had any problems with mover operation (voltage drop etc) with the control box being that much further from the battery?

 

[Mel]

Hi Paul. We have recently purchased but not yet taken delivery of a unicorn3. We also wondered about the battery box to mover distance and awkwardness thereof. Don't have an answer asnot got the beast yet but I'll be interested in any replies
Mel

 

[traficman]

Hi both we have a Unicorn 3 the dealer fitted our mover the isolation switch is fitted in the side locker on the kerbside it works fine but it must be at least 2.5 metres from the battery box.

 

[PaulT]

Hi both we have a Unicorn 3 the dealer fitted our mover the isolation switch is fitted in the side locker on the kerbside it works fine but it must be at least 2.5 metres from the battery box.

Which U3 have you got - is there not room to mount the switch in the mains inlet point?

 

[RONALD5555]

Hi Paul, I have a Unicorn 3 Cartagena. The Battery box is in the floor, under the fixed bed, with the mover control box and switch fixed to the inside wall of the bed just inches from the battery.

 

[ProfJohnL]

Caravan mover manufacturers usually supply lengths of suitable power cable, and it would be safe to assume that if you used all the cable they supply, the mover will still work correctly.

There is nothing magic about the power cabling for motor movers, it still follows all the basic rules of electricity.

It is sensible to keeping all cables as short possible, except some mover manufacturers suggest keeping all the power wires to the motors the same length, to keep cable losses to all motors the same. This in theory will balance the motor speeds, But for that to hold true, the motors will have to have identical performance, which in reality they will not. so it not an essential instruction.

The greatest cable losses are when the biggest current is flowing, so that will only arise when the motors are just starting to turn, but this lasts for a fraction of a second after which the current falls and the losses will also fall correspondingly.

Most mover manufacturers supply copper cable of 6mm" Cross Sectional Area (CSA) From standards tables this will drop 7.8mV per Amp Per Meter.

So to put that into context, of Volts drop per meter

a)A 60A start up current b) 20A running current
0.468V/m 0.156V/M

Don't forget that you have two cables per motor so assuming both the 12V and 0V cables are the same length, simply double the losses for a single cable.

TYpically a mover with 4M long cables will produce (0.468V x 4M x 2) = 3.774V drop per motor at start up with a (0.156V x 4M x 2) = 1.248V drop during normal running.