Monday, Mar 23, 2009 at 13:31
Ian,
Even below 75% SOC the Ranox unit (at 25A output) will still charge quicker than a straight alternator output. Your assumption is that given correct size cabling, the
battery will accept the alternator's spare output. But it is not just cabling (important though it is) that determines how much the
battery accepts, but the voltage differential. Decent sized cabling serves to ensure that the voltage at the
battery is a close as possible to that output by the alternator.
If the differential between the alternator output and the
battery is small, then it doesn't matter how much amperage you have, the
battery will not accept the charge at a decent rate. Increase the voltage differential, which is what units such as the Stirling and Ranox do, then you will force the
battery accept increased charge.
As an example, my previous set up relied on straight alternator input to charge a 100Ah AGM aux
battery, through an isolator (Redarc). I had fitted (don't ask me why) a 20A breaker at the cranking
battery end. Over several years of use in a wide range of conditions and at varying states of charge for the aux
battery, I never popped the breaker once.
Along comes the Ranox. Same
battery, same cabling (6 B&S), same alternator, same everything but with the Ranox set at 25A max output. OK for a while, but the first time I went camping and used the
battery for the weekend, I noticed that the
battery wasn't charging, no power to the Ranox unit. Cursing, I did some more investigation and realised that the 20A breaker was tripping. Reset it and same again. Replaced the breaker with a 40A one, and no more problems.
So what this tells me is that, despite having ample alternator output, my aux
battery never drew more than 20 Amps, regardless of its SoC from a straight alternator to
battery set up. I honestly don't know what rate the
battery charged at under the old set up as I never measured it. But it was certainly less than with the Ranox fitted. Just because the alternator outputs heaps of gibbers, doesn't mean the
battery is accepting them.
Now, you can make an argument that Ranox should have designed their unit to output more than 25A and you can make an argument that the Stirling offers better, features, reliability, value for money, etc. That is fair enough. But to suggest that the Ranox somehow 'chokes' alternator output is, as I said, misleading. My experience would suggest the opposite.
Cheers,
Matt.
FollowupID:
623657