Trying to understand DC/DC chargers

[Bear in NM]

Diplo,

Looks like we were cross posting. There you are, reading my mind again...

Yes,, I know I am over thinking, as one of my "regular" charge controllers will absolutely work. The Duo has the very nice dual battery monitor screens, and I thought it made sense to try and use what I have. I do understand that the relay closed should report the same volts on either battery, but I can see wanting to have the ability to check each bank with the solar off.

My initial install in the van will probably use the two 35ah in my solar suitcase. It is just enough in good conditions for my needs. I have two 80's in my cargo trailer, and that was plenty during my Oct/Nov hunt last year, with less than ideal conditions. Not a big electric hog when out, mostly just my fridge and led lights. And topping off my tunes, through a jambox.

I won't spoil it, but the Zodi is what will sometimes make or break whether a gal might be willing to go camping with you ;^) They are a bit of a pain to set up, but oh so nice. Pick a morning, put the word out to anyone needing it to cue up, and off to the races, with happy folks...

Craig

 

[4RunAmok]

There is some incorrect/missing information here.

The CTEK D250S while charging with solar, WILL, after the Auxiliary battery is sufficiently charged, route the solar charging to the Starter battery.

The Redarc WILL NOT do this. Talking with Craig from Redarc at SEMA, I mentioned that CTEK does this, and asked why they don't take advantage of that excess solar energy when the house battery moves to float charge, his response was that their focus is on the auxiliary battery only.

So if you wanted the solar to charge the main battery as well, you'll want a CTEK D250S, or its own independent solar setup.

 

[Joe917]

I don't understand the fixation with sending solar to the starter battery. Any vehicle with a good battery and a correctly operating charging system(alternator) should be able to be parked for weeks at a time with no issues. Send the solar to the house batteries and be done.

 

[dstock]

I don't understand the fixation with sending solar to the starter battery. Any vehicle with a good battery and a correctly operating charging system(alternator) should be able to be parked for weeks at a time with no issues. Send the solar to the house batteries and be done.

Many of today's modern vehicles, like my 2013 Jeep Wrangler, have factory systems that run all the time and after a couple of weeks with no charge will in fact run down to the point the vehicle will not start. Having a dual sensing system works very nicely as both the start and the house batteries are maintained.

 

[teotwaki]

I don't understand the fixation with sending solar to the starter battery. Any vehicle with a good battery and a correctly operating charging system(alternator) should be able to be parked for weeks at a time with no issues. Send the solar to the house batteries and be done.

I don't understand your discomfort with sending unused solar energy to top off the starter battery. If the house battery is fully charged why not switch the solar power source to charging the starter battery? Don't say it is more complex to do so. The CTEK already measures the voltage of each port and has MOSFET switches on all three ports. It was simple to route the output of the MPPT solar controller circuit to either the starter battery or the house battery. I know because I've had mine apart.

 

[Joe917]

I am not "uncomfortable" with it. I don't see it as much of an advantage. So buying one charger over another is not a plus for me. Needing to top up the starter battery is not needed, unless you stay parked a very long time or you have problems with the starter battery. So why not?
Usually not needed, extra cost of charger, extra wire run. If you think its needed go for it.

 

[Bear in NM]

Joe,

My van is a 6l turbo diesel. The start and run requires 12v battery voltage to be ramped up to 48v. This is handle by what is called a FICM. This is much like a normal vehciles PCM in that it contains a circuit board, is serialized, is pretty expensive, and is sensitive to reduced input power. They routinely fail, and are a pain to have repaired. While the van is new to me, everything I have researched indicates that I do not want to let my start batteries get low. And by low I mean yes it will crank, but reduced enough to be hard on my FICM.

I also have a 49mv "parasitic" draw on my system (as noted by dstock above). Per what I have been able to find, this is not atypical for a Ford. I am actually at 53mv with my Scanhauge plugged in. This number is about double the recommended draw for a typical vehicle.

With the FICM in mind, my sitting draw and the fact that my van is not a daily driver means I need to pay attention to my start batteries. The PO of my vehicle has a trickle charger wired into an AC plug along with the block heater. He noted to me that my van behaves best when always plugged in. I made a note, and after my research and testing figured out why he was using the charger. I have one of those cheapie cigarette plug trickle solar chargers working, until my big panels are mounted.

Craig

 

[CampStewart]

I get that if you are using solar you want to be as efficient as possible but if you are running off the alternator it seems to me like you could use an inverter and run a 120v charger and be money ahead. I am thinking about using an inverter and a ctek 4.3 to charge the trailer battery.

 

[teotwaki]

I get that if you are using solar you want to be as efficient as possible but if you are running off the alternator it seems to me like you could use an inverter and run a 120v charger and be money ahead. I am thinking about using an inverter and a ctek 4.3 to charge the trailer battery.

Not very efficient:

Use car alternator's 13.6 volts to charge a starter battery
Run an inverter off of that battery to create 120 Volts AC (first conversion)
Plug a 120 VAC battery charger into the inverter to create 13.6 VDC (second conversion)
Charge a second battery with the 120 VAC charger

More efficient:

Use car alternator's 13.6 volts to charge a starter battery
Use CTEK or similar DC-DC charger connected to starter battery (first conversion)
Charge the second battery with CTEK's output

 

[teotwaki]

I am not "uncomfortable" with it. I don't see it as much of an advantage. So buying one charger over another is not a plus for me. Needing to top up the starter battery is not needed, unless you stay parked a very long time or you have problems with the starter battery. So why not?
Usually not needed, extra cost of charger, extra wire run. If you think its needed go for it.

I already "went for it" and have had the CTEK many years so no need to purchase a different DC-DC charger or to purchase an additional solar charge controller just for the house battery. Proper maintenance of the starter battery avoids future problems. While parked for days solar charging allows car accessories to be used without starting the engine to charge the starter battery, thus saving gasoline which must be carried on board the vehicle while out in the boondocks.

 

[CampStewart]

Not very efficient:

Use car alternator's 13.6 volts to charge a starter battery
Run an inverter off of that battery to create 120 Volts AC (first conversion)
Plug a 120 VAC battery charger into the inverter to create 13.6 VDC (second conversion)
Charge a second battery with the 120 VAC charger

More efficient:

Use car alternator's 13.6 volts to charge a starter battery
Use CTEK or similar DC-DC charger connected to starter battery (first conversion)
Charge the second battery with CTEK's output

I think that is what I stated in simpler terms. You may be loosing some efficiency by going from 12v nominal to 120 back to 12v nominal but will that loss of efficiency be measurable when running off the alternator which should have much more capacity than is being used? For me that small loss in efficiency is more than made up for in the cost difference between DC and AC chargers. If you disagree please provide some numbers to show how much gas is being wasted or how many more amps the alternator will have to produce when using the ac charger

 

[teotwaki]

.....The angst of engineering decisions must weigh heavy upon us...

Agree! Don't want to be stranded out in the middle of Nowhere!

 

[DaveInDenver]

I think that is what I stated in simpler terms. You may be loosing some efficiency by going from 12v nominal to 120 back to 12v nominal but will that loss of efficiency be measurable when running off the alternator which should have much more capacity than is being used? For me that small loss in efficiency is more than made up for in the cost difference between DC and AC chargers. If you disagree please provide some numbers to show how much gas is being wasted or how many more amps the alternator will have to produce when using the ac charger

You may have a point when comparing to a DC-DC supply, which tend to be very expensive indeed. Your typical 12VDC->120VAC inverter can be pretty efficient. Ultimately depends but if you size it right you might lose a few percent in the conversion. It's not make-or-break on an alternator. Would be more critical with solar probably.

Either way I think the limiting cost factor here would be the quality of the AC inverter. It's not a foregone conclusion that it will be a lot cheaper if you're forced to use a pure sine inverter if you find the cheaper ones either don't work or cause a shortened lifespan on the battery charger.

 

[DaveInDenver]

There is no free lunch...
But good benefit exists inverting to high voltage AC then to a mains voltage battery charger very much negates need for large AWG conductors over long distances. Also allow huge variety of comparatively low cost batterychargers.

Just at the risk of shock unfortunately.