DC Charging options

A DC to DC charger of the biggest capacity possible would be the go.
I take it you intend to run the ute battery while it is charging? I'd reckon it would need to be sitting on at least 1500rpm to provide enough alternator output though.
The other solution would be a gennie running a large capacity 240v charger.

Hi filosoph, for a start, as long as you use a genuine automotive grade AGM, like an Optima, Odyssey or Exide Orbital Spiral type AGMs, then you can charge and discharge them with as much current as you have available or need.

If your using any other AGMs and then you can expect a very short life span from these types of AGMs because the can not tolerate high current charging or discharging.

Next, unless you can afford a Stirling DC to DC 50 amp charger, you would be wasting money with these other toys.

By the way, the are quite a few Mobile Coffee Vendors who are using the Stirling units with great success.

As to the story about an alternator stepping once the cranking battery is full charged, this is just total crap.

Some alternators on different makes of vehicles, step back based on a time period from when the motor was started and have absolutely no idea if the cranking battery is fully charged or on it’s last legs.

Last but not least, with the charging current you need, give your alternator a chance to do what it’s designed to do and that’s to provide high currents when needed, like when your batteries are low. Your alternator will recharge the battery set up you have, much, MUCH quicker than any of these toys could ever hope to do, so just get a relay/solenoid type isolator.

Pat,

Not too sure about your measurements and actual requirements. I take it that when heating water the inverter is drawing 36 amps from the battery. That's a fair load on any deep cycle battery, though if it starts out fully charged it should stand it for a while. The 50 cups is interesting - that's at least 10 litres of water to be boiled. I assume you don't aim to serve 50 cups one after the other? How many cups per day and how long does the machine run to produce a cup? This info will help us understand your actual electrical demand. Where does the idle current (26 ac watts) go?

"What is the better option a 100 – 200 amp Redarc like isolator or a 30 amp DC to DC charger?" The 100-200 amp rating is the isolator refers to the maximum current it can handle, not what it will supply. (That's determined by the capacity of the alternator and the nature of the load.) The isolator is there to separate the auxilliary battery from the main battery when the alternator isn't charging. Some are claimed to only connect the batteries after the main battery is fully charged - in my experience they connect almost immediately the alternator is working. You need some kind of isolator to do this. For your purposes I think probably your best solution is to use an isolator in the engine bay and a 30 amp DC to DC charger close to the battery.

What the sparkies are telling you about the alternators cutting back to a trickle charge after a while is sort of correct. (Actually, it is mainly the battery characteristics, not the alternator that determines the charge rate.) The charging voltage required by the main battery is temperature dependent, so the alternator output is made temperature dependent to match this. The alternator output voltage is reduced as the alternator ( and battery) temperature rises. One problem with simple charging systems for the auxilliary battery us that with the battery being stuck out the back somewhere it doesn't experience the temperature change. Due to losses in the wiring and the alternator voltage being reduced, the aux battery never gets a full charge. That is why a DC to DC charger close to the aux battery is a very good way to go. (These chargers take the available voltage and increase it up to what the deep cycle battery actually requires.)

With 2 auxilliary batteries in seperate locations as you have, it becomes a bit complicated, as you really need the dc-dc charger close to both. Would it be possible to put both in the van? If not, suggest give the charger to the battery running the coffee machine, and run heavy cabling from there to the second aux battery - not ideal, and there should be another isolator between them unless you want both to share the load - getting complicated.

HTH

John

Pat, before you can get a decent answer from anyone you need to correct the comment below and add details.

"My first auxiliary is in the back of the ute and runs an inverter to power and low powered coffee machine which draws a total of 36 DC amps to make 50 cups. (This data is based on hard empirical data i.e. I’ve tested and measured and retested and re-measured (and drank lots of coffee while testing). When the machine is idle, i.e. not making coffee it draws 26 AC watts."

This statement can not be correct and / or complete.

Either

a)the coffee machine uses 36 AH to make 50 cups ( and how did you measure that?) or
b)the coffee machine draws 36 DC amps while making the 50 cups ( over an unspecified time) or
c) Something else.

Sorry to be pedantic but without this information it is impossible to answer your question meaningfully.

Pat,

I second drivesafe.
Spiral wound lead/tin are the fastest lead acid batteries, in terms of current discharge and recharge.
They can accept charge from 0 to 95% within a lightning fast 45 minutes with the right charger/s.

And yes, they can be charged quickly by alternator up to 85 or 90% SOC.
If you come home, connect a good quality charger to it and let it top off the charge overnight.

Just by coincidence, I did a test a few days ago: put the spiral wound baby into the
Paj, and turned on the high beam. Left it sitting there for 2 hours 15
minutes, after which time the voltage had dropped to 11.8V under load.
Then I took the battery inside and used two 25A fast chargers* to
boost charge the battery at 14.8V at a combined max charging current of 50A.

I could watch the terminal voltage creeping up as the 50A pushed up the SOC
faster than the police would allow it. But surprisingly there was hardly any
warming of the battery, maybe 5 to 10 degrees above ambient if at all.
After 30 minutes or so, the voltage was 14.4V and the current started to
taper off. After another 15 minutes, the chargers went into float charging
mode, which signals a SOC of around 90 to 95%.
*(see photo of the setup attached)

Sorry, if I'm boring you with this, but I do this battery
charging/discharging/load testing thing on an almost daily basis. And from
what I've seen so far, these pure lead/tin spiral wound batteries react
extremely quick to applied charge, they just suck it in. They have me
excited as you might have guessed....
So if you're after really quick recharging times, this is the technology of
choice.
These batteries certainly will help you save in the long run, due to reduced
generator run times, and due to their longer cycle life.

Best regards, Peter

Hi Peter

Would it be possible to hook up multiple DC to DC smart chargers in the same fashion? Or would the isolator system still be best value , i.e. bang for buck?

Looks like the Triton has a 95amp ( or is it ampere) alternator. If the above rationale is continued would it be most frugal to get a 100amp isolator? If so what is the best one out there? Best one meaning bang for buck and might as well be this fiscal period.

On another point.

If the auxiliary battery/s is receiving 14.2 volts and the cranking battery and the red arc 100 amp isolator are receiving 14.45 volts is this an acceptable voltage drop?


I keep hearing different auto sparkies claiming that after the cranking battery is "full" then the alternator will only trickle charge. I dont see how this would be possible but I guess the only way to be sure is to some how measure the amps going into the battery not just the volts. I'm using one of those $20 multimeters to measure the volts.

Also how would I test the amount of amps going into the battery?

It's on a mates car that I've rewired for him. Cranking battery to his RedArc then to his 1st aux batt. then continued on to an Anderson plug to the 2nd aux batt in the trailer. the difference between the two batteries was .04 of a volt i.e. 14.24 in the 1st and 14.20 in the 2nd The 1st battery is in the back of the ute about 5 metres from the Redarc and the 2nd battery is about 8 metres

Pat,
when the Aux battery is connected direct to the Cranking battery by the battery isolator, the Alternator REGULATOR will only 'see' one battery voltage, this is the voltage of the two batteries averaged out together, because they are now wired in parallel and as such are basically now only one large battery.

The Alternator’s regulator should maintain the charge of this ‘large battery’ at the average 'float' voltage of ~13.8v.

This of course assumes the battery cabling is correctly sized and is secured solidly.

Maîneÿ . . .