Thread: Beware Charging Dual Battery in D4.

Originally Posted by RoverLander

Drivesafe, I accept that your system works. Its just that I can not see how it can fully utilise the capacity of the additional batteries. People are getting adequate time from their batteries because they are also drawing from the main vehicle battery (down to 12V). This is a solution that works best at the moment but it is not ideal.

Peter

Hi again Peter, and mate, you, like many others, have been sucked in by the garbage these DC-DC makers put in there advertising hype.

Fact, even though the SC80’s operating procedure is now over 20 years old, because of the way it works, an SC80 dual battery set up is still the FASTEST system for replacing used battery capacity.

The DC-DC devices are great for topping off auxiliary batteries but they can not compete with the way the SC80-LR works when fitted to a D3 or D4, or any other vehicle.

The more power you use between charges while driving, not only does the SC80-LR replace used battery capacity in a short drive time than any other set up, because of the way it works, it is also much safer for your batteries.

If you have a 100 Ah AGM auxiliary/house battery in your D4 and you use 80 amperes of power while free camping, with any other set up, you have to discharge your 100 Ah auxiliary/house battery down to 20% SoC.

With an SC80-LR, your battery only gets discharged down to about 57% SoC and check any battery manufactures info and they all say that regularly discharging any battery below 50% SoC begins to shorten their life span and the deeper the discharge, the shorter the life span.

Also note, that at 20% SoC, your have all the power you are going to get out of an AGM battery, and a flooded wet cell battery should not be taken below 30%, with the SC80-LR, at no extra cost, if you need more than 80 amperes, you have up to 125 amperes if you chose to take your 100 Ah auxiliary/house battery down to 20% SoC.

With any other set up, the only way your are going to get 125 Ah is to add another battery, BUT, now your are going to need to drive for a much, MUCH longer time to recharge this amount of Ah when using one of the DC-DC toys.

Where as with an SC80-LR and taking into account the lower operating voltage of the D4, you will still replace the used battery capacity in a much shorter driving time.

Sorry Peter but the is NOTHING out there that does anywhere near as good a job as the SC80 and SC80-LR do.

BTW, why is it not ideal to take a cranking battery down to 50% SoC ( 12.0v )?

Peter, one more point, if you find that with your DC-DC set up, you do need to add another battery, if you discharge them down a fair way, you will now need to drive for up to 90% longer to allow your DC-DC device the time it needs to full charge the two batteries.

If you need to add a second auxiliary/house battery to an SC80 set up, at most you may need to add 20% to your driving time and if you add a third battery, it’s still about the same time.

If you need to add a third battery to your DC-DC set up, add another 80 to 90% to your drive time.

It always amazes me how the sellers of these DC-DC devices always neglect to mention that the more auxiliary/house battery capacity you have and use, the much longer you have to drive to fully charge them.

Ahh Drivesafe... i'm enjoying our debate. I'm sure I'm an amateur grappling with an expert but let me have another go

So I see the advantages of the DC-DC "Toys" as:

1) will deliver a steady 20AMP at 15.5v regardless of what the vehicle alternator decides to do. (Well it would if the low voltage output of the D4 didn't get in the way).

2) They are capable of fully charging your second battery(s).

3) They deliver the higher voltages that the calcium battery makers recommend (I talked directly with Supercharge).

4) You end up with a fully charged vehicle battery that stays fully charged. I don’t want to run my main battery down to 50% out in the bush thank you.

5) I suspect it wouldn’t put as much strain on the electrical system as it doesn’t allow the alternator to try to charge all connected batteries at once possibly putting a significant load on the full alternator.

Disadvantage of DC-DC toys:

1) Doesn’t currently work due to D4 low voltage!!
2) It may not charge as quickly initially as the alternator in most cars will deliver more that 20AMP but at a lower voltage (14.5 I think)

Advantage of the SC80 “partial charger” – you started it
1) Cheaper that DC-DC charger
2) Faster initial charge
3) Simpler
4) Works today


Disadvantage:
1) Risks your main battery being partially discharged
2) Never fully charges your batteries (the D4 drops down to less that 12.7V once the batteries are partially charged to save precious fuel!
3) May put a strain on your electrical system that you don’t want.

The choice is up to each of us. But let’s try to make sure that we have the information to make our choice. Things have changed a lot in 20 years and the D4 is at the bleeding edge. If you are happy to partially charge your batteries and partially run down your main battery then choose a “partial charger”. If you want a full main battery and full second batteries, although taking longer to charge (possibly) then choose the DC-DC “toy”.

By the way I have two batteries connected (2X60AH). Charging works fine other that the problem already mentioned.

Hi RoverLander, the SC80’s operating set up may be 20 years old but it’s more relevant to day than any of these toys.

Now to your arguments, you TOY DC-DC device does not charge at 15.5v until the battery is nearly fully charged.

Again, it’s not much use having a device that will supposedly fully charge your Ca/Ca batteries if you don’t drive long enough to charge them in the first place.

As posted earlier in this thread, as the SC80 charges quicker than your TOY can so you are actually more likely to damage your auxiliary battery using your TOY because you are highly unlikely to fully charge them in the first place, a point that I see you have also conveniently neglected to mention.

BTW even with the way a D4 varies it’s charging voltage, I have yet to come across a single D4 owner with my SC80 in their D4, that does not fully charge ALL the batteries when they do their daily drive, so another myth with no substance. Especially when we take into account that you continually state your set up does not work!

Now this one did give me a laugh, how on earth can make up such farcical statement that one "would put a strain on the electrical system in a D4".

The D4 comes with a 180 amp alternator and have you ever had a look at the size on the cables LR put in the D4’s charging circuit. That statement is pour desperation in trying to make a point when there is no evidence to back it.

As for discharging your cranking battery down to 50%, whats the problem. Being as you can start most modern vehicle from as little 11.5v and thats 20% SoC, and this includes a D4, if you can’t start your D4 with a battery voltage of 12.0v, you already have a problem and your not going to start it with a full battery.

You can invent all the arguments you want but if someone is using a fair bit of power while camping, at the end of the next days drive, you are far, FAR more likely to have fully charged batteries when using an SC80 set up than you will ever have when using one of those TOYs.

Again, if you do tend to use a fair bit of power, your batteries are going to have a long operating life span if you use an SC80 rather than a DC-DC device, because a DC-DC device is much harder on your auxiliary battery, because you have to discharge the auxiliary battery twice as low as you do with an SC80 set.

Again, you can invent all the arguments you want and while your set up does not work, with all the people now, with D4s and my gear fitted, have you come across any of these people having your sort of problems?

So the SC80 is not only heaps cheaper but it will actually pay for itself by extending the life of your batteries.

My D4's batteries don't seem to suffer from not being charged enough using my VSR setup and I really don't care if they are not fully charged as long as they do the job. However I am somewhat torn between Drivesafe's system that has the advantage of being able to more quickly recharge multiple batteries that have been discharged a little (eg charging at up to 20A per battery) than a single battery that has been discharged a lot (still only charging 20A but for double the time) and having a 50% discharged starting battery being discharged further by the D4's electronics to the extent of endangering the ability to start the engine. While my VSR does the job I will stick with it but if my 2nd battery fails to recharge in time and slowly goes flat over a number of day's use (which did not occur with my TD5 D2) and the D4 proves reliable in not flattening its starting battery in normal use then I'll readily replace my VSR with an SC40.

Hi Graeme, I recently had a customer with a D3 who was having problems.

The cranking battery was going flat if the D3 was left for two or more days.

He went to two different auto electricians and both carried out load tests on the battery and both said the cranking battery was fine and the SC80 was causing the problem.

Well he rang me to tell me what the auto electricians had stated and then told me that he had to jump start from the auxiliary battery.

The SC80 was not only not the problem but had done it’s job in reverse.

He still had the problem a few days later and so went to e third A/E. Same story, so this time after he had been driving for 7 hours straight, he disconnected the SC80.

The battery was flat the next morning. While the SC80 was connected, the auxiliary battery was slowing down the discharge rate of the cranking battery.

At the end of this days drive, again quite a few hour of driving, he disconnected the cranking battery neg lead to see if it was the battery or something in the vehicle.

After just two hours he measured the voltage across the cranking battery’s and it was already down to 12v and was flat the next morning.

So much for the knowledgeable A/Es.

As a side note, when he jump started his D3 off his auxiliary battery, the first time when the SC80 was still connected, the auxiliary battery had been pulled down to 12v, the SC80 had disconnected the two batteries and then the auxiliary battery continued to power his fridge over night, but still had enough power to over come the flat cranking battery and jump start his D3 at the same time, the next morning.

So the point is clearly demonstrated that you can SAFELY discharge your cranking battery down to 12v and still have heaps of power to be able to start your motor when needed.

In tests, I have take the D4’s cranking battery down to 11.5v ( that’s 20% SoC ) and still been able to start the D4.

Thanks Drivesafe for the background reports. The battery is huge and the engine starts immediately, unlike some vehicles of old.

I can't tell if my VSR is cutting in and out as I drive but I do have a tailored dual LED battery voltage indicator setup that reveals the aux battery gets connected shortly after startup on cold mornings when the LEDs indicate that both batteries are overcharging by older standards. I could setup a remote LED from the VSR if I really wanted to know.

I have noticed since Q093 that the time before accessory shutdown has been significantly reduced, presumeably to save battery drain.

Hi Drivesafe, It's been interesting reading the replies regarding battery set up. Can I ask some advice. I have a D3 and a D2 and have removed the dual batteries from the D2 and want to install in the D3. The set up I used and also had in a GU Patrol prior was to link and separate the batteries using a 200amp solenoid. This was switched using the ignition, so car on batteries connected and charging, car off batteries isolated. My thoughts are a very simply system and never let me down. Can this be used on the D3? Would appreciate your advice.