Rotronics RBT 12

Uncle,

Here's some reference to the RBT unit from the Rotronic Web site RBT12 Isolator

Hi thanks for that Sandman I
'll look it up.Forgot to mention if anyone has a current Redarc system also charging their camper battery?

I'd suggest that the RBT12 won't make 2 hoots of difference to charge time. It will supply the same voltage as any of the other isolators, including your Redarc - assuming your vehicle has a decent size alternator.

Most critical thing for you will be the quality of the wiring and connectors you use as the resistance in the circuit over such a long length (I assume you'd need say 8-9 metres of cable) will become significant. You should have a fusible link at each battery for short circuit protection, and I'd suggest you use minimum 8Ga (and preferably 4 Ga) cable and Anderson plugs at the towbar. And don't forget the earth, which I'd wire all the way from the second battery to the engine block.

Hi Uncle,

As the RBT 12 is a charge/isolator, it will allow maximum alternator output to your van battery once your vehicle battery is fully charged. If you are using an AGM or similar "fast charge" battery, then this system will get your van battery charged faster than a redarc (or similar isolator) as it isolates the individual batteries and only charges one at a time.

However, the RBT 12 will only get your AGM type battery back to 90% capacity (see Rotronics web site). While it will get a normal wet cell battery back to 100%, the fast charge time is negated as they cannot accept too high a charge rate.

Additionally, if you have a 2nd battery in your vehicle, you will need the RDC12M so all batteries can be charged and isolated properly.

While a rotronics isolator will get a high charge current into a battery, only an AGM type can accept the fast charge but ironically can only recharge it to 90%. While a wet cell can be charged to 100%, it can only accept a slower charge and defeats the purpose of the fast charge aspect.

IMHO, you are financially better off with a redarc isolator and using an Arrid Twin Charge (ATC). The ATC boosts the voltage back up to ~14.2V to allow 100% recharge, but is limited to 15 amps, thus a slower charge time.

In my van, I used a redarc isolator to top up my 130Ah battery when away from power (probably best recharge was ~90% due to voltage drop over long lines) and a 240V 3 way smart charger to fully charge when back to 240V power. This worked well for me, but rarely away from 240V for more than 3 days OR without a long drive to really top up my battery.

Cheers

Captain

This Rotronics System is Guaranteed for 3 Years and information available by talking to people on the road using them is they actually work as specified by Rotronics :-)

I originally had a Redarc and found it unsatisfactory, when I enquired I was informed they are 'not recomended' for different types of batteries, so I installed a Pirahna system, then upgraded to a Rotronics RDA12 system, at least I don't have battery problems now.

Contact Rod at Rotronics for factual information, with-out any inuendo or double speak!!

The Rotronic argument is that (one of) their units isolates the house battery and this gives it 100% access to available charge. Thus the starter battery does not deplete the house battery charge. This statement is true.

Nevertheless here's the facts of charging.

A starter motor pulls 200-450 amps but only for a second or two. Belief this or not (but I'll prove it to you if you don't!) this is actually a very small amount of energy. It's about what a sidelight _Affordable_Storage_Drawers.aspx in 15 minutes. The alternator replaces this within a minute or two. From thereon that battery _Affordable_Storage_Drawers.aspx only fractions of an amp.

The Rotronics unit gives the starter battery priority. It then isolates it. The current saved is that which would have SUBSEQUENTLY flowed to that starter battery.

But unless that battery is close to buggered - that's diddly-squat (fractions of an amp). There ARE theoretical benefits but I have yet to be convinced there are worthwhile practical benefits.

Redarc or similar relay does effectively the same. It gives the starter battery priority, but does not subsequently isolate it.

But none of the methods of parallel charging will bring any conventional lead acid battery much beyond 70% charge. AGMs have a far greater charge acceptance and will charge close to 100%.
Collyn Rivers