duel batter system question: DC/DC or Isolator

[bignev]

Hi all,

The next addition to the white money pit is a dual battery setup.

USAGE - unfortunately I don't get away for weeks on end, more like 1 week at a time but mostly two or three days. Want to be able to run the 45L Fridge Mate, camping lights, future water pump, and charge electronic gizmos (perhaps low wattage inverter for charging camera etc).
Eventually I would like to get a camper trailer so a couple more batterys, solar and so on.

Plan to get a 100ah deep cycle battery (not sure what type, need to research more on that)

My main dilemma is do I need a Charger such as Redarc BCDC 1240 @ 479 (includes cables etc) OR will an Redarc Isolator of some sort at quarter of the price suffice?


I know there there many advantages for/against each system but given my intended (and possibly future) use, will the extra hard earned dollars spent be worth it?


Regards,
bignev
______

[macca]

Cuppa's the man, he has done a lot of research on this.
12v - 12v charge the battery to maximum so is handy if stopping more than a day or two. The 1240 has facility for solar input so future proofing your investment might be worth it.
Cuppa has done all of this using these components so his advice is worth listening to.

[First Patrol]

I'm in the same boat mate looking at doing the dual setup but the do it once properly way. What I read on other post cuppa is your man and that's who I'll be trying to talk to just before I part with my $$$$
Try a search on here there a lot of info
Good luck

[Cuppa]

With you future plans the dc to dc without doubt. If you fit an isolator (VSR - Voltage Sensitive Relay) now, there will come a time when you realise that that you are not fully charging your batteries.
I keep banging on about this because in the long run the dc to dc charger gives you a far better deal.

Take your 100ah deep cycle battery.
Charge it from your alternator (via an isolator) ....... max charge it will get to is perhaps 80% capacity ..... 70% more likely unless on long drives. (This is true regardless what you might hear - go ask any battery specialist)
For a deep cycle battery to get it's intended 7 to 10 year lifespan it should not be discharged beyond around 50% capacity routinely. (Occasionally down to 40% is ok)
70% minus 50% = 20% = 20Ah = not much from your 100Ah battery - chances are your fridge will use double that overnight.

If however you fit a dc to dc charger which will charge the battery to 100% you now have have an available 50Ah which is 2.5 times the capacity you had available with the VSR!

So go with the dc to dc, as whatever battery capacity you end up with it will fully charge it, unlike just going through the isolator, & if you go with the BCDC1240 (or Ctek equivalent) you wont need to buy a separate solar regulator when you get your panels.

I think there are two reasons folk go with the VSR's these days ..... either to save initial cost or because it's what they (or their mate) knows. Dc to dc smart chargers have made VSR's 'old technology.


Cuppa

[gaddy]

Ive always used VSR style systems but after reading all of the info cuppa has put in this and previous posts , and my own research will be changing soon . Pre kids we used to be always moving or at least driving every day and never had a issue now that we do a days driving and then 2 days just camped the second battery is suffering ,
Thanks cuppa now I gotta tell the missus I want to spend more money

Steve

[bignev]

Thanks all for the advise. looks like i will get the redarc bcdc

[megatexture]

Don't rule out the more affordable ctek 250sdual http://www.baintech.com.au/chargers/ctek-d250s-dual, basically the same thing and can take up to 250watts of solar input. though only 20amp it can be run in conjunction with a ctek smartpass unit that brings it up to 80amps http://www.baintech.com.au/marine/ct...anagement-unit
I've had mine for 4 years now and haven't even thought that I might need the smartpass

[Cuppa]

An amendment to what I wrote. I had missed that bignev's fridge was a 45 litre one, so my comment
"Chances are your fridge will use double that overnight" is a bit of an overstatement. Nevertheless it still makes sense to make full use of your battery's capacity. Gaddy makes a good point ..... Your 'pattern' of travelling makes an enormous difference in what works, or doesn't, for you. This is why my Patrol has 360ah of Aux batteries & 425w of solar in addition to the BCDC1240. With 125w solar on the cab roof it's designed to only need to get the 300w of portable solar out if camped without driving for more than 3 nights, & to allow for a minimum of a week camped without driving in poor solar weather, whilst providing self sufficiency in power indefinitely. I envisage being camped in places for as long as food & water supplies last, potentially several weeks at a time, before travelling on......... Clearly very different power requirements to weekends away or travelling every day.

Cuppa

[kevin07]

definitely check out the ctek its only 2 hundred now boom that's a lot of charge for ya buck

[Cuppa]

I've had mine for 4 years now and haven't even thought that I might need the smartpass

I have never really understood why Ctek have chosen to limit the D250s Dual to 20 amps, requiring the additional Smartpass unit to increase charging current, when it could easily all be done in one box. There is no doubt that Ctek is quality gear, & I have never heard anyone complain about their choice to buy the 'Dual'.

It was my lack of understanding for the need for two separate units if more than 20 amps charging rate was required that saw me choose the Redarc, that and the fact that 20amp capacity was less than I needed for my solar panels output. If The BCDC1225 had been released when I was buying, I may well have chosen it, but I have since come to understand there can be good reasons for fitting a larger amp unit, so now I would still choose the 40 amp unit.

Regarding the need for a higher charging rate, this is another horses for courses issue involving pattern of usage as well as battery capacity. If ctek's Smartpass is required to boost the 'Dual's' charging amps the Redarc's cost becomes competitive. Either will do the job just fine unless there is a specific need for the full 80amp capacity of the Smartpass (In which case an alternator upgrade may also be wise. Folks I know who have used their full alternator capacity for more than short periods - charging LiFePo4 batteries - have found alternator life to be short).

With bignev's future camper plans I would think that he may be better off considering a higher than 20amp charge rate.
The higher the rate the faster it will bring the battery (ies) up to 3/4 full, (less driving time) but after that charging amps are reduced & an 80amp or 40amp charger will only be able to put charge into the battery at the same rate as a 20amp charger. The important part is that it (a smart charger) will still put in, which an alternator alone won't, but because the higher amp charger had put the bulk charge in sooner, it has more opportunity during your driving time to bring the batter(ies) up to full, & /or allow the solar to do so before it gets dark. The 20amp unit is better suited to longer driving periods and/or smaller battery capacities. IMHO of course.

Oh, and another advantage of using a dc to dc charger (aka battery to battery charger - B2B) of whatever brand in a dual battery system is that unlike an isolator solenoid it allows for a different charging voltage for the aux battery, useful if you have two different battery types ( Eg. a 'wet' crank battery and an AGM aux battery) where each have differing charging requirements. Basically another factor in treating the batteries more kindly to extend their lifespan.
Their ability to boost available voltage is also useful in accommodating voltage drop from long cable runs (eg. To camper trailer) & thus should be mounted close to the battery which is being charged.

Cuppa