Thread: Aux battery sugestions

Hi Tanks, and what has been posted above is spot on the money.

Your DC/DC devices can improve the charge VOLTAGE at your Optimas but to get 20 amp out to the Optimas, your alternator is going to have to supply close to 30 amps, catering both for the inefficiency of the DC/DC device and for the energy lost in your cabling between your alternator and the DC/DC device.

This is exactly what I posted about earlier when I stated that you have a problem in your system and for the DC/DC device to correct the the low volts at your auxiliary and house batteries would have increased the current draw on your alternator.

From the picture, you have either 6B&S ( 13.5mm2 ) cabling or 8B&S ( 7.9mm2 ) cabling.

It is a bit hard to tell from the picture, just what size it is.

If you have a YELLOW CRIMP TERMINAL, unused, hold the Yellow barrel next to the red cable and if the cable is 6B&S, it will be just about the same diameter of the Yellow crimp terminal.

If the cabling is 8B&S, then the cable will be noticeably smaller then the barrel of the Yellow crimp terminal.

Either way, if you paid $30 per meter for that cable, and it is 6B&S, you have been ripped off because it is around half that price or less and if it is 8B&S, then you have paid 3x the price you should have.

If it was the same place that advised you to fit the DC/DC device, I would avoid them like the plague!

If the cabling is 6B&S, and it looks like it might be, then if those two Optimas were in a low state when you were driving home, they could have easily drawn 60 to 70 amps while charging and would have been fully charged by the time you got home.

If the cabling is 8B&S, then there is the reason your batteries only partially charge on the trip home, because 8B&S is way to thin.

Originally Posted by drivesafe

Hi Tanks, and what has been posted above is spot on the money.

Your DC/DC devices can improve the charge VOLTAGE at your Optimas but to get 20 amp out to the Optimas, your alternator is going to have to supply close to 30 amps, catering both for the inefficiency of the DC/DC device and for the energy lost in your cabling between your alternator and the DC/DC device.

This is exactly what I posted about earlier when I stated that you have a problem in your system and for the DC/DC device to correct the the low volts at your auxiliary and house batteries would have increased the current draw on your alternator.

From the picture, you have either 6B&S ( 13.5mm2 ) cabling or 8B&S ( 7.9mm2 ) cabling.

It is a bit hard to tell from the picture, just what size it is.

If you have a YELLOW CRIMP TERMINAL, unused, hold the Yellow barrel next to the red cable and if the cable is 6B&S, it will be just about the same diameter of the Yellow crimp terminal.

If the cabling is 8B&S, then the cable will be noticeably smaller then the barrel of the Yellow crimp terminal.

Either way, if you paid $30 per meter for that cable, and it is 6B&S, you have been ripped off because it is around half that price or less and if it is 8B&S, then you have paid 3x the price you should have.

If it was the same place that advised you to fit the DC/DC device, I would avoid them like the plague!

If the cabling is 6B&S, and it looks like it might be, then if those two Optimas were in a low state when you were driving home, they could have easily drawn 60 to 70 amps while charging and would have been fully charged by the time you got home.

If the cabling is 8B&S, then there is the reason your batteries only partially charge on the trip home, because 8B&S is way to thin.

The 2 optima batteries have never been in the Disco, the Disco aux. battery was a Supercharge 120 amp Deep Cycle.
The $30/m cable is the battery/isolator/winch cables on the Disco, the battery cable in the C/T came from a Telstra Mobile phone tower battery power pack, the red and black wires from the Disco to C/T are too thick to fit a Yellow crimp connecteor, probably half as thick again, I had to buy 6mm lugs and solder them on, all the other power wires in the pic were yellow crimp size.
So what everyone is saying is that DC/DC chargers are a gimmick and DO NOT charge an aux battery from an alternator supplied battery, if I can get a signed statement from someone suitably qualified I will take my C-TEK back and demand my money back and maybe even contact Fair Trading, thing is it has worked extremely well, can anyone tell how to treat that green stuff on one of the soldered terminal lugs, Thanks again for the info, Regards Frank.

Originally Posted by THE BOOGER

Yep both going well been spending a bit of time at westmead getting transplant tuned
As for the DC DC charger to produced 13.7 volts from 12.8 takes power that csn only come from your alt or your starter bat

Geoff, hope the tune up gets you back on the road again, the power for the DC/DC charger comes from the alternator charged starter battery, the Anderson plug at the rear of the Disco (from the starter batt.) reads 12.8 volts with the engine not running, same reading at starter batt., the cable is at 6mm dia. high quality copper both + and -.
With the engine running 13.8V at both ends and the DC/DC charger receives 13.8V from the starter batt. or 19V from the solar panel (max input to DC/DC charger is 21V).
I haven't charged the C/T yellow top batteries for a few months and they are down to 12.4V, if I hook the Disco up via the anderson plug and drive for around a half hour they will be up to full charge 12.8 to 13V so the charger seems to be working. I figured the alt. would be working hard to charge and maintain 4 batteries and I would still face the same problem of 3 Aux. batteries not receiving any charge till the hard worked starter battery was up to 12.8V. I can see no other solution except using a manual switch to charge the aux. batteries at the expense of the starter batt., has anyone got a solution to this, good to hear from you, Regards Frank.

Originally Posted by Tank

So what everyone is saying is that DC/DC chargers are a gimmick and DO NOT charge an aux battery from an alternator supplied battery

Hi again Tanks and that is not what people are saying.

Your DC/DC device is going to charge your batteries, but we are all trying to point out that if your setup was operating properly, you would not need any form of DC/DC device and all your batteries would be charged far fast when being charge straight from the alternator.

And once again, with that size cabling, you should be able to easily fully charge your batteries with out a DC/DC device. Mate, there is something seriously wrong!

Originally Posted by drivesafe

Hi again Tanks and that is not what people are saying.

Your DC/DC device is going to charge your batteries, but we are all trying to point out that if your setup was operating properly, you would not need any form of DC/DC device and all your batteries would be charged far fast when being charge straight from the alternator.

And once again, with that size cabling, you should be able to easily fully charge your batteries with out a DC/DC device. Mate, there is something seriously wrong!

I get what you are saying, normally both batteries in the Disco are always around 12.8V each.
BUT when I go bush, as in the 17 hour recovery I did the other night, continual slow driving 10 to 15klm/hr, lights on, wipers going (rain and sleet), numerous stop and start, and a couple of hours of winching.
At daybreak I checked the voltage of the start battery and it was down to 12.4V.
I joined the Aux (not deep cycle) to the start batt. when I noticed the winch struggling, the aux batt, in the morning was down to 12.4 as well.
I had to return to Moruya workshop and pick up some more chains as we had damaged a few of the recovery slings, 35klms. each way, checked both batteries when I got back to the recovery, both batteries were back up to 12.9V.
I believe the major cause of the original deep cycle battery (supercharge 120 amp) not getting a full charge on the way home when I was out camping was the similar treatment of the starter batt. as described above and the fact that the Engel fridge would drag the Aux. battery down to as low as 7 V..
After fitting the DC/DC to the inside footwell of the Disco and hooking it up to charge the aux. I had no more problems till a month or so later the aux batt. dropped a cell and would not charge over 10V on my home based Durst charger. Replaced buggered deep cycle with a good second hand batt. out of one of my trucks and never had a problem. When I purchased the C/T I switched the DC/DC over to the C/T as in the pics and switched back to the redarc 100 dual batt. system on the Disco with no problems.
I was wondering if I should do away with the Dual battery system (Redarc) and just wire the 2 batteries together in the Disco and what causes that green crap on some of the soldered connection lugs, please, Regards Frank.

Quote: " Mate, there is something seriously wrong",
yes I believe you it is/was the fact that the Redarc system didn't allow the aux. batt. to receive enough charge in the time from when the start batt. was at 12.8V., to when it sent a charge to the aux. batt. another half hour of highway driving would have seen the aux battery fully charged.

This is what I based my installation for the Camper Trailer on, Regards Frank.

DC TO DC CHARGERS A DC to DC charger uses voltage from one battery to charge another and typically they do not connect to 240V (although some models are coming on the market with this additional feature). DC to DC chargers solve some of the following charging dilemmas:

Charging Different Battery Types As we learned earlier there are many different battery styles (Flooded, AGM, GEL etc) and each type has its own quirks when it comes to charging. Flooded batteries which are the most common vehicle batteries typically charge at around 13.8V-14.1V in a vehicle however if we put an AGM in as the second battery they like to charge at a much higher voltage so straight away we have a problem. A quality DC to DC charger will step up the voltage being sent to the second battery so that it receives the appropriate charge voltage and it will apply a Bulk, Absorption and Float charge. Something a VCR can never do!

Alternators Do Not Fully Charge Vehicle Batteries Most of you will be shocked to know that your fully charged car battery is only about 80% charged.




As we learnt earlier, a battery needs to go through several stages of charge to achieve full saturation. A vehicle’s charging system is just not capable of providing the right levels of charge. Therefore an Isolator or VCR will also fall short. Most modern DC to DC chargers will provide these additional charging stages so that you get the full potential from your second battery. After all, what would be the point of buying an expensive second battery if you are only going to get access to 80 – 85% of its capacity?

Long Cable Runs One big advantage DC to DC chargers have over a traditional VCR is that they step up the voltage to better suit Deep Cycle batteries. This step up in voltage can also assist to recover voltage drop in longer cable runs. This becomes a problem when the second battery is in the boot or mounted in a caravan or camper trailer.

DC to DC Hints and tips If your DC to DC charger has a temperature sensor then I would run that sensor out into the cold air stream. As you head further towards the Equator, temperatures slowly rise and so do under bonnet temperatures. The temperature sensor is designed to protect the battery by reducing charge if the battery gets hot (which commonly occurs when a battery has been in Bulk charge for extended periods). So the rise in under bonnet temperature de-rates the charge. Not all DC to DC chargers are temperature sensed in this way!

Testing Tips If you suspect your DC to DC charger is not working, it is critical that you test both the input and output voltages. They can simply turn off due to the fact that the vehicle has reduced its charge below the cut in threshold.


THREE BATTERY SYSTEMS Here is a quick question to see if you are paying attention:

If you already have a dual battery system and you want to install a third do you connect it to?

A. The Second or Auxiliary battery in the system, or B. The Start battery

If you chose B. then you would be correct. If you are installing a third battery you should always treat the third exactly the same as the second. The exception to this rule would be if you were adding a third battery to increase the Amp Hours capacity. And to do this you would join the second and third batteries in Parallel.

Why connect the Third to the Start Battery?  If the Second or Auxiliary battery is low it may take some time to bring the voltage back up to a point where the third battery will cut in (assuming you are using a VCR or DC to DC charger for the Third battery).

 If you are pulling loads off the second battery while charging this could drop out the VCR or DC to DC charging the Third battery.






Here is an example to help make all of this a little clearer.

"Diagrams did not copy", but I followed precisely, Regards Frank.

Frank, what are the connect and disconnect voltages of your Redarc dual battery isolator? What is the maximum output current of your DC-DC device?

Tim, what are the connect and disconnect voltages of the dual battery systems that you produce?

Frank, when you ran the Redarc dual battery isolator, where did you take it's feed from? Did you check for voltage drop across connectors, connecting wires and earth straps?

Aaron

Originally Posted by Aaron IIA

Frank, what are the connect and disconnect voltages of your Redarc dual battery isolator? What is the maximum output current of your DC-DC device?

Tim, what are the connect and disconnect voltages of the dual battery systems that you produce?

Frank, when you ran the Redarc dual battery isolator, where did you take it's feed from? Did you check for voltage drop across connectors, connecting wires and earth straps?

Aaron

Mounted as per Redarc instructions, i.e. as close to the main batt. as possible, about a foot away, not sure but most seem to think it is 12.7 to 12.8, leads big enough, no drop in voltage anywhere.
Have checked voltage of both main and aux. batteries after sitting for a couple of weeks, main might be down to 12.6 (clock and fuel gauge work 24/7) before starting and I have noticed that there is no charge to aux. for 5 mins or so.
But when out camping and doing as described in above posts it can take up to 1/2 an hour before the aux gets a charge and it was nearly always below 11 volts, in the hour trip home it would be up to around 12V., so would put it on home charger to top up, if I drove for a longer period the aux would reach full charge, thanks for the input, Regards Frank.