Thread: Do I need a BCDC charger?

Originally Posted by muddy

what about using an inverter on a microwave/coffeemaker etc

You'd be drawing that from the house batteries, surely.
The connecting cable is usually to keep the house batteries charged whilst driving. A few amps is ample.

Think about it. What is the size of the cable from the alternator? 4mm2?

Originally Posted by Mick_Marsh

When are you going to get an 80A load in the trailer?

Voltage is supplied, current is taken, it's a capability. More to the point though it's about voltage drop at high current load.

The bigger the cable cross section area the less the voltage drop and the greater the efficiency in power transfer from the vehicle to the trailer and the more efficient running of high power devices. A flat trailer battery will never charge properly via small diameter cable as the voltage drop in delivering power to it is too great. ie. If you've got a dead flat aux. battery in the trailer you can drive all day with 5 metres of 6 mm automotive cable (actual 4.5 mm sq) between it and the vehicle battery/alternator for bugger all result. As cable size increases losses decrease at an exponential rate ie. doubling the cable size quarters the power loss to the aux battery and allows the charging voltage to reach a level where it can effectively charge the trailer battery. DC-DC chargers were designed to help overcome this limitation and do it well when used appropriately but do nothing for overall power transfer for a high current load. As I said "there's no such thing as cable that's too big"

Deano

The bigger the cable, the less volt drop you have over the length.

Originally Posted by Milton477

The bigger the cable, the less volt drop you have over the length.

And as the battery (we're talking lead/acid here) charges, the current reduces, therefore, the voltage drop in the cable reduces.
As the current approaches zero, the voltage drop approaches zero, and you get full voltage at the battery terminals.

You size the cable accordingly.

Originally Posted by Mick_Marsh

You'd be drawing that from the house batteries, surely.
The connecting cable is usually to keep the house batteries charged whilst driving. A few amps is ample.

Think about it. What is the size of the cable from the alternator? 4mm2?

case where using higher current
I have a similar set up on the back of the puma with 175 Anderson plug and a 50 Anderson (2inch of cable between ) and when we have storms like at present we may loose power to house --as a result no water (PUMP) or refrigeration making it easy to get the inverter plugged in and all's good at the same time mindful of the battery volts .Then see if the generator is necessary from shed

the size of cable between alternator and battery is also a limiting factor for charging

Originally Posted by John_D2

Poop...I forgot that. I only left about 4 or 5” of wire between the 2. I’ll see what I can do. 50amp ok?

Hi again John, there is a simple fix and it will not effect your system’s operation.

replace the 80 amp fuses with 60 amp fuses, job done and everything will then be operating within safe perimeters.

I use 50 amp auto resetting circuit breakers for that little extra safety and never had a problem.

Originally Posted by rangieman

Why not a use a resettable circuit breaker instead of a fuse .
Resettable 12V 80A Automatic Alloy Fuse Holder Car Audio Circuit Breaker | eBay I run one very similar between my DBC and a 50a anderson plug on the rear

I’ll keep it in mind. Thanks

Originally Posted by drivesafe

Hi again John, there is a simple fix and it will not effect your system’s operation.

replace the 80 amp fuses with 60 amp fuses, job done and everything will then be operating within safe perimeters.

I use 50 amp auto resetting circuit breakers for that little extra safety and never had a problem.

Just a bit curious now. In a perfect world with the moon & planets aligned, how much current could you run between a dual & 3rd battery that’s 8-10m away?