Thread: Dual battery system that always works

Originally Posted by Dunnie

Voltage sensing solenoids (not relays) do the trick fine.

Hi Dunnie, there is actually no electrical difference between a solenoid and a relay, they are one in the same.

Cheers.

Hi Wilbur, there are only two vehicles that work with this low charging voltage as a normal operating voltage level, the D3 and RRS and they only run at this voltage once the battery monitoring electronics determines that the cranking battery is fully charged.

This is where other dual battery systems ( DBS ) come unstuck, the vehicles battery is rapidly charged as it has only been used to start the vehicle and the auxiliary battery(s), which have been used to power accessories, will not be fully charged but the vehicle’s electronics can’t see this and simply lowers the charge voltage to prolong the operating life of the cranking battery.

The SC40-LR and SC80-LR get around this problem because of the unique way they operate.

There are also problems with other DBS where the D3 is driven for a while and then stopped while the owner refuels and/or has lunch.

If there is any form of load, say a fridge or what ever, this load will quickly cause the battery voltage to drop below the DBS’s cut-out voltage, which is higher than a fully charged battery’s voltage but lower than the lowest charging voltage and the DBS thinks the motor is off ( correctly so ) and isolates the auxiliary battery.

All’s well so far.

After the stop, the D3 is started and the owner drives off thinking the D3’s alternator is not only running the fridge but it is topping off his auxiliary battery at the same time.

Unfortunately this is not the case. After the break, when the D3 is started, the electronics sees that the cranking battery is near fully charged and that the operating temperature under the bonnet is now high, so it deems that there is no reason to have a voltage higher than what is needed to maintain all the vehicle’s electrical requirements without risking overcharging the cranking battery. 13.2 is the lowest operating voltage and this is too low to trigger the cut-in setting in the DBS.

Now you have a ( common ) situation where the fridge is running off the auxiliary battery which is NOT being charged and at the end of the days drive you have an upset owner.

The SC40-LR and SC80-LR are specifically designed to avoid this situation.

Originally Posted by Wilbur

If I had one of the modern 3 stage alternators there would be no choice. A step-up system would be essential. That is the way things are going, before long most or all new vehicles will have the 3 stage system - it is cheaper than putting in a bigger battery!

Paul

Hi again Wilbur, what you will see in newer vehicles is the same type of continuously varying charge voltage system that the D3 and RRS have.

This type of charging is designed to charge the battery as quickly as possible to optimise battery life.

Cheers

Hi Drivesafe,

Yes, that all makes sense, and that is pretty much what I expected.

I am not actually sure what the SC40 and SC80 are, but you seem familiar with them.

I presume that once they trigger, even at 13.2 volts, the extra load of the house battery and fridge etc would fool the alternator into thinking that the vehicle battery was low enough to justify putting out its 14 odd volts.

Not sure how the vehicle battery would like this, being charged at 14 volts most of the time, but I doubt it would grumble too much.

It is certainly a much simpler and more robust arrangement than having a voltage step-up - and heaps better than the inverter-charger route!

Interesting, very.

Cheers,

Paul

Originally Posted by Wilbur

I am not actually sure what the SC40 and SC80 are, but you seem familiar with them.

Paul

Hi Wilbur, I make the SC40-LR and SC80-LR but I’m not trying to do any advertising, just show that there are different and cost effective ways to achieve fully charged batteries from the alternator.

Cheers

i can do the advertising for you.......


but seriously.......i put the SC40 in lurch about 3 years ago.......

the only time i had a problem.......was when my main/cranking battery died......

as i didnt have any jumper leads......i just swapped the terminals over and ran on the aux battery till i got a new battery....about a month later......

that aux battery is still in there and works fine.......havent had a single problem.....

and the SC40 was much cheaper than the other brands........



since the d3 came out with its fancy electronics......i think the SC40 had to be slightly modified to suit......
and i think its also the only dual battery management system recommended by land rover.......


just send drivesafe a pm with any questions you may have.......and im sure he will have the answers......
he has always had answers and solutions for any probs i may have had in the past.....

Hmm.....my face a bit red.....

Sorry Drivesafe, now I know why you seem so knowledgable on the subject!

Where do I find info on your units?

Thanks Defenderzook for your ad - sounds pretty enthusiastic. Nice to see some things made in Australia instead of China.

Cheers,

Paul