Dual battery system that always works

[Wilbur]

Hi All,

The current thread on dual battery problems shows that there is a real need for a proper system, one that will work whatever the charging voltage of the car system is without affecting the car charging regime, and give proper three stage charging to the second battery.

It would need to have a user-selectable cut-out voltage so that the user could decide how low they woud allow the car battery to drop, and a user-selectable second battery type to optimise the three stage charging for the particular battery.

This is all easy, known technology but it would not be cheap. It could cost around $400 for a 20 amp system, and maybe $600 for a 40 amp system.

The big question is, would anyone pay that much? It seems unlikely, or there would be some on the market already.

Any thoughts?

Cheers,

Paul

[DEFENDERZOOK]

i think the SC-40 does just that......it charges the aux battery off the main one........
till the main starts to drop.......then it isolates it.......

so the main is always charged.........with more than enough power to crank the engine over.......



being connected to the main battery.....it will also use some of the surplus power from that......
which will give you power for longer than just the aux battery can supply on its own......

[Wilbur]

Hi Defenderzook,

The problem is that as Drivesafe says, some modern charging systems provide only about 13.2 volts under some circumstances. The second battery needs about 14.5 volts to charge quickly and completely.

Thus what is needed is a controllable voltage step-up device capable of pumping 20 to 40 amps, and that's the expensive bit. It also needs the usual isolating circuitry but with adjustable voltage levels to suit personal needs.

Cheers,

Paul

[Signal1]

Hi All,

The current thread on dual battery problems shows that there is a real need for a proper system, one that will work whatever the charging voltage of the car system is without affecting the car charging regime, and give proper three stage charging to the second battery.

It would need to have a user-selectable cut-out voltage so that the user could decide how low they woud allow the car battery to drop, and a user-selectable second battery type to optimise the three stage charging for the particular battery.

This is all easy, known technology but it would not be cheap. It could cost around $400 for a 20 amp system, and maybe $600 for a 40 amp system.

The big question is, would anyone pay that much? It seems unlikely, or there would be some on the market already.

Any thoughts?

Cheers,

Paul

Piranha quoted over $1000 to fit a dual battery system so i think, yes, people do pay for a good system. Or are you saying that it would be $400 on top of the $1100 Piranha Unit

[Wilbur]

No, I was thinking it would cost around $400 to $600 all up for a complete unit, boosting output volts to 14.5 volts regardless of input volts, and including the usual isolating cut-outs etc.

That is probably not a retail price - I looked up retail prices of the appropriate bits on the net as a DIY project. I guess in commercial production they would sell for more - but not $1100!!!!

Do you know if the Pirhana system includes voltage step-up?

Cheers,

Paul

[mcrover]

And Pirahna systems are crap.

I have 2 in the shed 1 with a burnt circuit board from running the fridge, they said thats normal and just run a wire over it and solder it on :mad: and the other is a smaller unit that they dont recomend you use if you have a winch as the voltage drop can damage it apparently:mad:.

Im going to build my own basic simple system and just give the aux battery a full charge on the plug in charger before we go away anywhere.

[mcrover]

No, I was thinking it would cost around $400 to $600 all up for a complete unit, boosting output volts to 14.5 volts regardless of input volts, and including the usual isolating cut-outs etc.

That is probably not a retail price - I looked up retail prices of the appropriate bits on the net as a DIY project. I guess in commercial production they would sell for more - but not $1100!!!!

Do you know if the Pirhana system includes voltage step-up?

Cheers,

Paul

No the old ones that I have dont, they are just battery voltage but I dont know about any new ones they could have.

[Dunnie]

Voltage sensing solenoids (not relays) do the trick fine. They parallel the batteries if and when the reserve battery needs it and separates them otherwise. The auxilliary battery(ies) get(s) the full charge when needed. Batteries in parallel last longer and give more power than separate batteries. We do this on our boats at work all the time with zero problems. We use the Sure Power Smart Solenoids ex. USA that ARB used to retail. Redarc (Australia) do them as well. My Defender and SIII both use these so does the ute at work with an electric/ hydraulic crane on it. A piece of cake to install and an absolutely bullet-proof solution.

[mcrover]

Voltage sensing solenoids (not relays) do the trick fine. They parallel the batteries if and when the reserve battery needs it and separates them otherwise. The auxilliary battery(ies) get(s) the full charge when needed. Batteries in parallel last longer and give more power than separate batteries. We do this on our boats at work all the time with zero problems. We use the Sure Power Smart Solenoids ex. USA that ARB used to retail. Redarc (Australia) do them as well. My Defender and SIII both use these so does the ute at work with an electric/ hydraulic crane on it. A piece of cake to install and an absolutely bullet-proof solution.

It's Redark that Im getting, I cant remember the Amps but I will be isolating it when winching anyway with a big red key switch but at around the $100 from my auto elec mate it is a much better and simpler system for me.

Electrickery is never great on things like 4wd's that get used in extreme envioroments (for electronics that is) I have found.

They dont like dust, vibration, oil and fumes, heat and water and then it still is meant to work.

If you were not using your 4B of road all that much and mainly towing or the like then it wouldnt be much of a problem.

[Blknight.aus]

Voltage sensing solenoids (not relays) do the trick fine. They parallel the batteries if and when the reserve battery needs it and separates them otherwise. The auxilliary battery(ies) get(s) the full charge when needed. Batteries in parallel last longer and give more power than separate batteries. We do this on our boats at work all the time with zero problems. We use the Sure Power Smart Solenoids ex. USA that ARB used to retail. Redarc (Australia) do them as well. My Defender and SIII both use these so does the ute at work with an electric/ hydraulic crane on it. A piece of cake to install and an absolutely bullet-proof solution.

thats a very similar setup to the one I like to use but the major difference is the sense wire comes off of the alternators second output OR the alternator side of the exciter feed which in essence means that the only time the 2 batteries are hooked together is when the alternator is turning AND making charging voltage.

[Wilbur]

Yes, I agree, simple is best in a 4b. However, I built a camper on the back and I installed a 110 litre Waeco upright fridge/freezer, and the insulation is so skimpy that it runs nearly half the time.

The result is a max of one day stopped on my 100AH house battery, and then it needs about 8 hours driving to do another day.

If I boosted the charge voltage from 13.8 to 14.5 I would expect a significant improvement.

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!

One way or another, we will all have to deal with this issue eventually.

Rgds,

Paul

[drivesafe]

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.

[drivesafe]

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.

[drivesafe]

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

[Wilbur]

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

[drivesafe]

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

[DEFENDERZOOK]

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.....

[Wilbur]

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

[mns488]

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

http://www.traxide.com.au/

I've got one as well, never had any problems.:)