Redarc Dual Battery System - Which one?

[martynvella]

Might not be the right thread for such a post but it has gone in this direction.

When bansheebuzz put up that post he would have been expecting the response it has generated.
nobody is looking at the whole picture, yes the scenario he described is an extreme one so there are the people that come back and say been doing it like that for years, mixture of never been to such an extreme and luck. Half of his post refered to the batteries being under charged but the point you all missed is, push an alternator hard enough for long enough and it will fail.

Alternators are only 50% efficient meaning for every watt of electrical energy it produces it produces a watt of heat, heat that has to be removed by its cooling system. At low revs there is very little air being moved through the alternator to remove this heat and late model alternators, whilst not developing full output will charge enough at idle to get very hot inside. Ask Nissan patrol owners, those fitted with the hitachi units with the vac pump on them almost always had a fried positive diode in them from sitting round idling with the AC on, most would run till worn out like this but the owners would continually complain about poor performance of dual battery systems of the day.

I have always used the rule of thumb of try not to ask more than 60% continually of the rated output.

Later model units have gone to dual cooling fans so might up that a little but not much.

The best way to combat this potential problem is to get one of those larger bodied and output alternators,
have a sparkie remove the 120 amp stator and have it would with slightly lighter wire with a few more turns to aim for about 90 amps total output (so it doesn't blow the alt fuse). The winder will work it out.

This will cause higher low speed output or earlier cut in and the physically larger rectifier and cooling fans will be able to cope with the heat much easier.

Not a lot of people do this because it is expensive and would rather spend the money on more light bars and things that look fancy but make the problem worse.

[Lundy]

Hi Guys,

I went the redarc BCDC1220 ... 20amp DC-DC and im glad i did, and didnt get the 40 amp.

REason being is that I quite easily have an alternator shortfall ... even with the 20 amp.

that is, if i am idling, especially in gear (auto) , my alternator output is minimal... so much so that my redarc often puts itself back to sleep because the main battery circuit drops below 12.7v.

It's made much worse if either battery are actually low and in need or hefty charging.

Now, it's mostly not an issue, and if i am idling on tracks at night with spotlights on , i tend to use an IDLE UP switch i instlaled, which brings engine rpm to 1100rpm and therefore alternator at full tilt ... but only just.

If i'd gone for the 40amp charger, I think this "shortfall" would have been much more prominent, and the redarc would have been in a constant state of charging charging, BAIL BAIL.

The good thing is that the redarc does shut itself off (therefore overall the solution prioritises charging / protection toward the starter which is what you want...).

btw, the redarcs (mine anyway) has ignition wire, it only ever runs if the ignition is on and voltage is above 12.7 on starter.

Hi Querty, i have the same redarc system as you. I read on a pdf from the redark website that the BCDC1220 is only recommended for a battery bank of 50-100ah. Do you know if there would there be a problem with having a main, a 70ah second battery and a 130-150ah third, ( so approx300ah total) apart from it just taking longer to charge? i would also be relying on solar to charge when not driving so a really high charge while driving is not really needed

[martynvella]

Hi Guys,

I went the redarc BCDC1220 ... 20amp DC-DC and im glad i did, and didnt get the 40 amp.

REason being is that I quite easily have an alternator shortfall ... even with the 20 amp.

that is, if i am idling, especially in gear (auto) , my alternator output is minimal... so much so that my redarc often puts itself back to sleep because the main battery circuit drops below 12.7v.

It's made much worse if either battery are actually low and in need or hefty charging.

Now, it's mostly not an issue, and if i am idling on tracks at night with spotlights on , i tend to use an IDLE UP switch i instlaled, which brings engine rpm to 1100rpm and therefore alternator at full tilt ... but only just.

If i'd gone for the 40amp charger, I think this "shortfall" would have been much more prominent, and the redarc would have been in a constant state of charging charging, BAIL BAIL.

The good thing is that the redarc does shut itself off (therefore overall the solution prioritises charging / protection toward the starter which is what you want...).

btw, the redarcs (mine anyway) has ignition wire, it only ever runs if the ignition is on and voltage is above 12.7 on starter.

Hi Querty, i have the same redarc system as you. I read on a pdf from the redark website that the BCDC1220 is only recommended for a battery bank of 50-100ah. Do you know if there would there be a problem with having a main, a 70ah second battery and a 130-150ah third, ( so approx300ah total) apart from it just taking longer to charge? i would also be relying on solar to charge when not driving so a really high charge while driving is not really needed

This question has already been covered in this thread, but if you are in doubt ask redarc themselves, they will say yes or no, and give the reasons why.

Here are their contact details,



Mailing Address

P.O. Box 469,
Morphett Vale,
South Australia, 5162
Australia




Phone & Fax

International
Phone: +61 8 8322 4848
Fax: +61 8 8387 2889

Local
Phone: (08) 8322 4848
Fax: (08) 8387 2889

Please post your findings.

[Qwerty]

Hi Guys,

I went the redarc BCDC1220 ... 20amp DC-DC and im glad i did, and didnt get the 40 amp.

REason being is that I quite easily have an alternator shortfall ... even with the 20 amp.

that is, if i am idling, especially in gear (auto) , my alternator output is minimal... so much so that my redarc often puts itself back to sleep because the main battery circuit drops below 12.7v.

It's made much worse if either battery are actually low and in need or hefty charging.

Now, it's mostly not an issue, and if i am idling on tracks at night with spotlights on , i tend to use an IDLE UP switch i instlaled, which brings engine rpm to 1100rpm and therefore alternator at full tilt ... but only just.

If i'd gone for the 40amp charger, I think this "shortfall" would have been much more prominent, and the redarc would have been in a constant state of charging charging, BAIL BAIL.

The good thing is that the redarc does shut itself off (therefore overall the solution prioritises charging / protection toward the starter which is what you want...).

btw, the redarcs (mine anyway) has ignition wire, it only ever runs if the ignition is on and voltage is above 12.7 on starter.

Hi Querty, i have the same redarc system as you. I read on a pdf from the redark website that the BCDC1220 is only recommended for a battery bank of 50-100ah. Do you know if there would there be a problem with having a main, a 70ah second battery and a 130-150ah third, ( so approx300ah total) apart from it just taking longer to charge? i would also be relying on solar to charge when not driving so a really high charge while driving is not really needed

apparently something to do with resistance and yes the BCDC1220 is probably too small for a bank like that.

That's a big bank... and coming back to alternator capacity / efficiencies as others suggest, probably too big for the vehicle with stock alternator ... ie a bit overweight.

Up to you though, perhaps you're going to have different charge sources like an AC-DC charger on generator at times? Or a large solar array?

It'll work, just slowly.

Btw there's some flaws in your suggestion.. your two "aux" batteries that will hang off the BCDC need to be the same size, and chemistry or you're going to fry one, and under charge the other.

The starter is not relevant, it remains charged / connected to the vehicle and alternator only.

In short, the redarc DCDC is just an "appliance" that requests power from the alternator.. just like a stereo or fuel pump. It delivers charge then to the aux circuit.

YOur auxillary circuits are to be wired on an isolated circuit, and will only ever draw current from the aux battery.

Different scenario to a smart solenoid where the second battery is simply bridged to the main circuits whilst voltage is above a certain voltage. Kind of more work involved in a DC DC scenario (but there are many benefits {and arguments})

[Qwerty]

Might not be the right thread for such a post but it has gone in this direction.

When bansheebuzz put up that post he would have been expecting the response it has generated.
nobody is looking at the whole picture, yes the scenario he described is an extreme one so there are the people that come back and say been doing it like that for years, mixture of never been to such an extreme and luck. Half of his post refered to the batteries being under charged but the point you all missed is, push an alternator hard enough for long enough and it will fail.

Alternators are only 50% efficient meaning for every watt of electrical energy it produces it produces a watt of heat, heat that has to be removed by its cooling system. At low revs there is very little air being moved through the alternator to remove this heat and late model alternators, whilst not developing full output will charge enough at idle to get very hot inside. Ask Nissan patrol owners, those fitted with the hitachi units with the vac pump on them almost always had a fried positive diode in them from sitting round idling with the AC on, most would run till worn out like this but the owners would continually complain about poor performance of dual battery systems of the day.

I have always used the rule of thumb of try not to ask more than 60% continually of the rated output.

Later model units have gone to dual cooling fans so might up that a little but not much.

The best way to combat this potential problem is to get one of those larger bodied and output alternators,
have a sparkie remove the 120 amp stator and have it would with slightly lighter wire with a few more turns to aim for about 90 amps total output (so it doesn't blow the alt fuse). The winder will work it out.

This will cause higher low speed output or earlier cut in and the physically larger rectifier and cooling fans will be able to cope with the heat much easier.

Not a lot of people do this because it is expensive and would rather spend the money on more light bars and things that look fancy but make the problem worse.

I came close to fitting a 300amp alternator, but then got a brand newie for free from toyota (mud killed first one i think) ... and have been OK since, just have to micromange my loads a bit... and use my idle up switch. Sensible decisions like when idling i dip down to low beam and dont leave my spotties and lightbar and foggies lit. THe foggies for some reason (100 watts each) really draw hard. Just common sense stuff, but without a volt meter in dash, wouldn't probably be aware of it.

If i kill my alternator, i'll replace it, just like any other part on the car...

[Lundy]

Hi Guys,

I went the redarc BCDC1220 ... 20amp DC-DC and im glad i did, and didnt get the 40 amp.

REason being is that I quite easily have an alternator shortfall ... even with the 20 amp.

that is, if i am idling, especially in gear (auto) , my alternator output is minimal... so much so that my redarc often puts itself back to sleep because the main battery circuit drops below 12.7v.

It's made much worse if either battery are actually low and in need or hefty charging.

Now, it's mostly not an issue, and if i am idling on tracks at night with spotlights on , i tend to use an IDLE UP switch i instlaled, which brings engine rpm to 1100rpm and therefore alternator at full tilt ... but only just.

If i'd gone for the 40amp charger, I think this "shortfall" would have been much more prominent, and the redarc would have been in a constant state of charging charging, BAIL BAIL.

The good thing is that the redarc does shut itself off (therefore overall the solution prioritises charging / protection toward the starter which is what you want...).

btw, the redarcs (mine anyway) has ignition wire, it only ever runs if the ignition is on and voltage is above 12.7 on starter.

Hi Querty, i have the same redarc system as you. I read on a pdf from the redark website that the BCDC1220 is only recommended for a battery bank of 50-100ah. Do you know if there would there be a problem with having a main, a 70ah second battery and a 130-150ah third, ( so approx300ah total) apart from it just taking longer to charge? i would also be relying on solar to charge when not driving so a really high charge while driving is not really needed

apparently something to do with resistance and yes the BCDC1220 is probably too small for a bank like that.

That's a big bank... and coming back to alternator capacity / efficiencies as others suggest, probably too big for the vehicle with stock alternator ... ie a bit overweight.

Up to you though, perhaps you're going to have different charge sources like an AC-DC charger on generator at times? Or a large solar array?

It'll work, just slowly.

Btw there's some flaws in your suggestion.. your two "aux" batteries that will hang off the BCDC need to be the same size, and chemistry or you're going to fry one, and under charge the other.

The starter is not relevant, it remains charged / connected to the vehicle and alternator only.

In short, the redarc DCDC is just an "appliance" that requests power from the alternator.. just like a stereo or fuel pump. It delivers charge then to the aux circuit.

YOur auxillary circuits are to be wired on an isolated circuit, and will only ever draw current from the aux battery.

Different scenario to a smart solenoid where the second battery is simply bridged to the main circuits whilst voltage is above a certain voltage. Kind of more work involved in a DC DC scenario (but there are many benefits {and arguments})

Thanks for the advice. I am looking at getting two of the same batteries so it should be compatible. I may look at something smaller, maybe just 200ah total auxiliary. I'll have to put up with the longer charge time i guess, i don't want to fork out more money but with 240w solar when stopped im guessing it should be alright?

[Qwerty]

all depends on your load. 240watt should def be enough to cover a fridge and some camp lights, in modest temps, by keeping the 200ah bank up at full charge with occasional dips in SOC overnight.

But like anything, all depends how you use it, if you brought those 200ah bank down to nearly flat, then you're going to need some time to recharge them.

All depends who you are, how you run things ... what your drives are like, how many times you add hot things to your fridge ... how many lights you choose to run. Whether the mrs wants an inverter for something. Parked in shade, or got some clouds.

Personally when i prep a trip i boot the fridge a few days before, and when mrs adds all the hot stuff in, i chuck in some ice bricks with it while fridge is off to stop it raping the aux ... and/or i plug my 240v AC-DC charger onto it ... so basically everything is totally topped up before I pull out of driveway... then rest of trip is basically about maintaining it.

Even so, it still goes south when i go adding lots of hot stuff to it when camping ... or crank the stereo (a deck and 2 amps that pull from my auxillary, kill it in no time).

Often one of my mates will bring a genny to camp anyway, so i just bring my AC-DC and keep it primed using that.

[Lundy]

Cheers mate, just trying to get some ideas and prep for a trip. I don't have any big stuff like amps, just general fridge, lights, small speakers etc so im hoping it will be alright. This stuff is all new to me... thanks again.

[Qwerty]

yeah man all good. I think you'll be sweet. Just trial and error, get good volt meters and get to know your system (read the manuals and know what it does at different voltages etc... i can usually tell exactly what my situation is just by what voltage is read, and knowing other factors like what SOC was before i started up, temperatures, loads etc).

but then im a nerd and love to micromanage stuff.

[Lundy]

yea i guess ill have to micromanage the others charging their phones and opening the fridge etc

[Qwerty]

one of my mates made a screwup the other day on mine. He loves to get in and turn wipers on, fans on, mess with all the settings so that next time you startup you get a shock ... but he also turned my bloody headlights on on high beam by accident.

2hrs later, i went into my car, starter voltage 8.1v (may well have busted it chemically, but so far it's OK).

Just jumped it off the auxillary battery (nice to have) and then let alternator charge for a few hrs... then ran my ac-dc charger as soon as i got home next day, which ran a 7 stage conditionning routine over it.

Needless to say there was a few "sorry mate, sorry" going around camp ha ha.

[Lundy]

i wouldn't be a happy camper if my mates did that

[Qwerty]

Yeah was an accident of sorts

[mattwhite]

In complete honesty Marty I have nowhere near as much experience with alternators as you.

I've seen first hand the sbi12's switch on and off at idle and knew why. Mainly on old cruisers but give them some revs and they're away. What I was trying to get at and am clearly wrong was that I thought the bcdc range would have the 'intelligence' to not pull the starter down to the point of not being charged. I find it disappointing they haven't moved on from this downfall of the sbi range.

I still stand by my comments that a lot of people spend a lot of time off of idle. But yeah, I was wrong.

[Qwerty]

End of day our modern vehicles have all sorts of Eco friendly , emissions targeted, fuel conserving systems that seem to always get in the way of our 4wding n camping needs.

[martynvella]

In complete honesty Marty I have nowhere near as much experience with alternators as you.

I've seen first hand the sbi12's switch on and off at idle and knew why. Mainly on old cruisers but give them some revs and they're away. What I was trying to get at and am clearly wrong was that I thought the bcdc range would have the 'intelligence' to not pull the starter down to the point of not being charged. I find it disappointing they haven't moved on from this downfall of the sbi range.

I still stand by my comments that a lot of people spend a lot of time off of idle. But yeah, I was wrong.

That is a very good point, they may have, they got so many different variants it is hard to compare.

Hard to design an add on to a system that has been fine tuned for economy rather than practicality.

[Donk]

This should open up a bag of worms. After waiting for an email reply from Redarc regarding information and prices on the BCDC1225 unit I also checked with them that the LV model is the unit I need for my model. Their reply was that the LV model is not required although it seems that 90% of people on here run the LV over the standard BCDC. What are the pros and cons of running either unit?

[Qwerty]

I dont run an LV variant,. V6 petrol 2007. Doesn't have all that low voltage problem that the newer ones do.

[quinny525]

I have 2013 diesel and they told me not to use the LV model, and it works fine

[martynvella]

it is just easier to wire up than the lv and might be cheaper, but if your going to use the solar you need the ignition wire anyway. What reasons did redarc give?

One advantage I can see is that if you remove it in years to come you know it will work with whatever you want to put it on.

on another note, I fitted a bcdc1240 to a 24 volt truck with 12 volt solar last week, for 20 amps in it gave 40 out, it really gave those batteries a wake up call, really kicked ass. I was expecting good performance but this thing cranked out full output for a solid half hour before the light started flashing and the unit got very warm as did the 30 amp input cct bkr but it was not what I would call hot, I was more than impressed.