DC-DC CHARGER RUNAWAY DISCHARGE WARNING.

THE EXPLANATION IS HERE:

This is not a problem I’m trying to solve. And neither is this a mystery as to why it happened. My diagnosis has been verified by professional auto electrical and DC charger manufacturers. It's not my opinion. It's my EXPERIENCE. And this is a warning to those who may be interested. NOTHING MORE!

If you charge the starter battery with AN EXTERNAL charger, the DC-DC will. WILL. OKAY. IT WILL . . . activate itself and begin charging the aux battery. THIS IS HOW DC-DC CHARGERS WORK!
If the external charger's capacity is less than your DC charger's it will drain the start battery in the process of charging the aux battery. IT WILL! This is also logical.

If you use a trigger cable from the ignition, and you leave the ignition on with the engine not turning, the DC charger will stay on until a pre-determined low voltage is reached, and switches off. That voltage may be too low to start the engine. I'm not guessing.

Now, you will only know if the full starter battery discharge has happened IF AND ONLY IF the charge is interrupted BEFORE THE CHARGE OF ALL BATTERIES IS COMPLETE. If you do not interrupt the charge, you won't know and all will seem fine. But the start battery has undergone a full discharge and recharge.

So. To avoid a runaway discharge, just charge the aux battery first. It's that simple! Or you may be caught with a flat start battery.

Now if you disagree, get this. There is nothing to disagree with! I am recounting an experience and presenting a warning. Use it OR don't use it. That's for you to decide.

[paullee]

All good info Andrew, I have had many problems to solve with battery issues as well. But I must say that it has been about 50 years since I left an ignition turned on with the motor off. I always use the trigger wire and a solenoid to connect the BC-BC. Cheers! Good Stuff!

[sleeharvester]

Love what you are doing with this series Andrew! Could you do a video on what compulsory maintenance we should be doing before trips? I am not very Mechanical savvy and would love a guide. Thanks.

[lukehair]

What do recommend too fix that as I've just setup duel system 400ah batteries with 40amp DC 2 DC 400 watt solar. I was thinking a switch to to turn DC on off but a drunk Aussie would probably forget just about to do a lap of this little country only about 30-40, 000km or more but my wife sensible could possibly remember. Love your show and she and Toyota god love Toyota 30 years plus now and thank-you cheers 🍻

[DIESELTECH_ZA]

I'm a firm believer to always isolate a battery when using a 220V AC charger, regardless whether using 1 or multiple battery systems.  It simply eliminates any possible issues from occurring.  Thanks for the heads up Andrew!  :)

[Ozjourney]

In my setup I have a breaker where your fuse is and I can quickly switch off the Aux circuit when I need to charge the main battery and often leave it off where not on trips just using the roof solar to keep the Aux topped up.

[danieljackson]

I was installing a BCDC 1225 this weekend, and found your clip pretty interesting. My install was in a camper, and it got me thinking… This issue looks like the starter battery needs to be better isolated from the house battery, and possibly it makes sense to treat it like a camper install and use a solenoid or an SBI to only link them when the ignition is on?

[jasonpotts]

Great video, Andrew and some excellent tips for us all. I'm using a manual cutoff switch in the dash for the DC-DC charger so that I can override the charger even when igintion is on.

[glenecollins]

How is the apparent charging voltage being maintained? As soon as the 50amp charger turns on it should pull the voltage down to just the battery voltage plus a little for the amount of power the charger can put in.
Unless the DC to DC charger is set to run down to 13.2V or something that shouldn’t let the starter battery discharge to below where it can crank over your cruiser.

If it is set to a very low cut off Voltage there should be a way of turning that up, with your setup the charging voltage shouldn’t fall below about 14v.

Try measuring the voltage at the starter battery with theAC to DC and the DC to DC chargers running

[FastFless]

Andrew, this doesn't make sense. I have basically the same setup and haven't experienced this problem.


Typically DC/DC Chargers will switch off and stop charging the aux battery when the input drops below 11.8 volts. They typically won't turn on unless the input voltage is above 13.1 volts. So when you connected your mains charger to the battery, yes the voltage would have risen above 13.1 volts and the DC/DC charger would have turned on. This is the same principle and operation of the old Voltage Sensing Relays (VSRs).


However, it's understandable that your mains charger would not have been able to cope with the load (current draw) of both batteries (if both were discharged).


But what should have happened, is that the voltage from your mains charger would have progressively dropped as it wouldn't have been able to maintain the output current required to charge both batteries. Once the mains battery (with mains charger connected) dropped below 11.8 volts, the DC/DC charger should have turned off.


The mains charger would then have been able to again start charging the main battery and the internal resistance of the battery would start rising and so would its voltage (Ohms Law). Once it reached 13.1 volts, the DC/DC charger would kick in again, and the whole sequence would start again. The end result over time, should have been that both batteries would be fully charged.


So what's happened in your situation is a bit of a mystery.

[gregpaulsen]

Thank you Andrew I have just discovered your channel. This should end a long running debate among my friends. I had warned one of my friends that sitting on the beach listening to the test cricket will flatten your battery. It had happened to me. I suspected the trigger wire as you explain but he was adamant that the load from the radio could not possibly drain his starter. Sure enough I had to give him a jump start but he still didn't believe it was the radio at fault. Now we know it was probably a flat auxiliary combined with the the trigger wire connecting the two batteries.

[mickellis]

I have the solution for you Andrew.
I tow a camper trailer and in it I have a redarc BCDC40 to charge the two 100 Ahr AGM deep cycle batteries simply because of the distance from the car alternator and the resulting voltage drop. The problem is exactly the same, if the batteries in the camper were not fully charged when you stopped the DC to DC would drain the auxiliary battery to charge them.
To overcome this I have a 100 amp relay mounted in the back of the car prior to the anderson plug which is switched through an oil pressure switch so it will never charge from the cars auxiliary battery, in my case, unless the car is running, even if you leave the ignition on accidentally. Luckily I found this out when researching the wiring and installation of the dc to dc charger before the actual fitting and it works perfectly. You could do a similar thing in your vehicle.

[adidas]

Good point. I am about to install a redarc DC/DC into my jeep with an AGM and LiFePO4 auxillary battery and I have been looking for a AC battery charger to do what you are doing.

[bennyfarrugia]

Not an issue with CTEK 250sa with smartpass check it out ! Have had ctek on my cars now for 7 years and never flat batteries, and my car is not a daily driver either.

[RiveraD]

Thanks for the info. In my situation I have my start battery purely for starting only. (Nothing connected besides low amp accessories on switches) the start battery will also be monitored. Then from my starter battery, it then connects to a smart isolator before connecting to my secondary battery. The second battery then has all the niknaks. This works only for older cars.

[seanfrost]

Andrew, possible solution, mount a solar panel on your garage roof and run cables down for easy connect on to the yellow cable (solar input) on the Redarc. When the Redarc sense solar input, it will not accept input from the main battery. Therefore, as long as you only have your 10amp start battery charger on at the same time as the solar connected to the aux, then you will effectively have separated charging of batteries.
Regards, Sean

[seankearney]

Many thanks for the heads up on this. Just a couple of weeks into a van to camper conversion. I will add in an isolator in the circuit just to be sure. I was always taught never to leave the ignition on, that stems back to old petrol cars where depending where the points were your coil could burn out. We used to pull the coil wire off if we had to tow a dead car for the same reason.

[TheAussiebloke]

U should have ur BCDC charger on the trigger switch u mentioned. The trigger switch can also be connected to a wire that only receives voltage when the car is running. U could also add a breaker so as the BCDC charger doesn’t see the voltage when ur trying to charge ur

[darwiniandude]

Fascinating! Thanks for sharing your knowledge. This situation is certainly not one that people would immediately expect to occur. I’m about to design and roll out a system into a 4WD van and I will certainly put an isolation switch between the crank battery and my custom goodies - even just if starting with jumper leads etc I don’t want the aux system taking some of that load away.

[TerryOGrady]

I put a dcdc charger on my boat to charge a 100Ah lifepo4. The outboard light coil is only rated at 6 amps. After running for a couple of hours, the start battery was completely discharged. I suspected what you're saying as the problem. Thanks for confirming.

[dirktheron]

I love DC-DC chargers, but thought it to be common sense to isolate the primary and aux batteries before connecting a 220V charger anywhere in the system, even if charging the aux battery/s and the DC-DC charger won't let current through to the primary.
I always run a 12V 60A circuit breaker between the two battery systems, this way you can even use two 220V chargers at the same time to maintain both sets of batteries whilst the vehicle is not in use for some time.