12V DC-DC Chargers

[proper4wd]

It seems as though this is the newest, and possibly best, option for charging an auxiliary battery in your vehicle. Google searches bring up some good information from Australia but I can't seem to find much information from US sources about these things.

Anybody have any insight on the products from C-Tek, RedArc, or others?

 

[charlieaarons]

Check Sterling 12V-12V chargers.
They don't turn till primary voltage is at least 13.2V (alternator on) and they up voltage a bit for more efficient and complete charging of secondary battery.
http://sterling-power-usa.com/12volt-12volt45ampbatterytobatterycharger.aspx

Charlie

 

[proper4wd]

Looks like Sterling has some good products. Any reason why this unit wouldn't work at half the cost of the marine grade version?

http://sterling-power-usa.com/ProCh...-battery-charger-waterproof12volt-12volt.aspx

 

[madmax718]

I really should have bought the one I saw at cabelas at the closeout price...

 

[mhiscox]

I have the C-Tek 7002, and can't imagine how it could work any better. Does what it needs to do and seems incapable of screwing things up. There are 111 Amazon reviews if you want to learn all there is to know about it.

 

[proper4wd]

That C-Tek 7002 is just a regular battery charger that plugs into 120V though, at least from everything I can tell.

 

[DiploStrat]

Getting Charged

I am installing a Sterling 210 Ah A2B in my Tiger (http://sterling-power-usa.com/12volt-210ampalternator-to-batterycharger.aspx)

The big difference between the various models of A2B and B2B is the charging rate.

Rob Blackwell is using two B2B to get a higher enough charging rate on his Unimog. At last report he was very happy that he rarely has to use his genset now.

Some photos here: http://www.pbase.com/diplostrat/ndeke_luka

 

[dwh]

Looks like Sterling has some good products. Any reason why this unit wouldn't work at half the cost of the marine grade version?

http://sterling-power-usa.com/ProCh...-battery-charger-waterproof12volt-12volt.aspx

It'll work just fine. The only possible problem is the output limit - it can charge at up to 30a for up to 30 minutes, then drops back to a max of 20a after that. Depending on the size of your aux battery bank, you might want more (possibly a whole lot more) charging amps than that.

Most deep cycle lead-acid battery manufacturers specify C/4 (amp*hours Capacity divided by four) as the recommended bulk charge rate. A few are different, such as Odyssey which can handle an ungodly C*4 (and which pretty much no charger on the market could actually supply), but C/4 is a rule of thumb that will work for just about any deep cycle lead-acid battery.

So if you had a single 100ah battery, than the 20a (or less) average charge rate of the IP68 would be in the ballpark (though...technically...a bit lower than the 25a which would be optimum). If you had 4 100ah batteries rigged into a 400ah bank, then 20a max charge rate would be way below the 100a of charge you *should* be feeding to that bank. It'd still work though, it'll just take a long time to charge the bank.


A few guys here are running the CTEK 250s DUAL, and they've all had good things to say about the unit. It's a 20a dc-dc charger that also has an MPPT solar charge controller in it. With a max charge rate of 20a, again it's great for a small one or two battery aux bank, a bit small for anything bigger:

http://www.ctek.com/int/en/chargers/D250S DUAL/

Only complaint I've heard is that it's bigger than it looks in the pictures.

 

[mrFelix]

re the Dual D250S.......it is possible to parallel 2 of these together giving a 40 amp charger

 

[G35Vortec454]

I think the idea behind these dc-dc or alternator intelligent chargers are fantastic; however, I haven't convinced myself to use one since I installed a 200A Delco 28SI alternator in my rig. Perhaps someone here can tell me what I'm missing.

The Delco 28SI has an internal regulator with a sense circuit. It is connected to my 660AH triple-bank house battery, as well as to the starting battery, via a 275W-rated isolator. Each of the three banks has its own digital voltage and current monitor; the alternator also has it own digital current and voltage monitor. I do not see any evidence of overcharging or undercharging from the alternator. It seems to me that the alternator regulator is intelligent enough (like a 3-stage charger, if not better) to push just the right amount of current and voltage based on the state of charge of the batteries. I have verified my findings, at certain states of charge of the batteries by not only switching the charging source to the generator-powered Prosine 3.0 inverter's 120A intelligent charger but also by checking the specific gravity of the batteries. The alternator charging rivals that of the inverter's charger, except the alternator can pump around 180A into the battery banks, hence shortening the bulk stage.

 

[verdesardog]

UM...what am I missing here? Why get another piece of gear for $$$$ when you can only charge your batteries at the maximum rate that your alternator can put out? There is no way that I know of that you can get more energy out of you alternator than it is rated at without burning it up.?????

 

[4x4junkie]

UM...what am I missing here? Why get another piece of gear for $$$$ when you can only charge your batteries at the maximum rate that your alternator can put out? There is no way that I know of that you can get more energy out of you alternator than it is rated at without burning it up.?????

You don't.
The idea behind a DC-DC unit is better charging precision (usually it has a sensor mounted on the battery itself for proper temperature compensated charging, along with an ability to "float charge" the battery if needed). A typical alternator isn't all that precise when it's temperature sensor (if it has one) is built into the unit itself and is next to a hot engine.

The Delco 28SI alt G35 mentioned sounds interesting though... Did you modify that or does it actually have hookups for remote temperature and voltage sensors? (got a link to more info on it?) Seems this would address many of the shortcomings of standard alternators, in which case I'm not sure the benefits of a DC-DC unit would be all that great.

 

[G35Vortec454]

You don't.
The idea behind a DC-DC unit is better charging precision (usually it has a sensor mounted on the battery itself for proper temperature compensated charging, along with an ability to "float charge" the battery if needed). A typical alternator isn't all that precise when it's temperature sensor (if it has one) is built into the unit itself and is next to a hot engine.

The Delco 28SI alt G35 mentioned sounds interesting though... Did you modify that or does it actually have hookups for remote temperature and voltage sensors? (got a link to more info on it?) Seems this would address many of the shortcomings of standard alternators, in which case I'm not sure the benefits of a DC-DC unit would be all that great.

No mods to Delco 28SI. It has a 257F overtemp protection switch but never seen it trip. No temp probe at batteries for alt charging; Temp probe at the batteries is only for shorepower/generator charging (so I guess that's the missing component for alt charging). The alt has 2 fans, front and back. The internal VR has remote sense. Note: batteries are NOT in hot engine compartment.

http://www.delcoremy.com/getattachm...I-Installation-Instructions-10524210.pdf.aspx

With a partially discharged battery bank, I've ran the alternator at extended periods at over 200A running a 11,000 BTU A/C drawing via the inverter 130-140A DC and the triple battery banks drawing the rest of it.

Here's my setup (the alternator current and voltage monitor not shown - on dash). The 3 digital current/voltage switchable monitors show the 85.8A discharge from battery banks; the ACS panel showing -92A used to power 110V accessories. Solar is harvesting 19.62A at the moment.

 

[4x4junkie]

Very nice setup!

So it has just a remote voltage sense lead then... Certainly that's one more than most alts have though.

I would say if you're not having issues with your batteries reaching full charge (and no issues with overcharging), there shouldn't be a whole lot of reason to invest in a DC-DC unit.

 

[G35Vortec454]

It'd be nice if there is an add-on blackbox with a temp probe and a logic circuit that taps into one of the internal regulator terminals that effectively controls the alternator's field current to drop or raise the float charging voltage deending on temp change.

For a 660AH bank, however, I'm not sure a half-volt drop matters much when temp changes from 70F to 120F, for example. At least I am not expeiencing abnormal water loss or acid corrosion on the batteries. I think the heat generated inside the isolator and the resulting higher votage drop at higher temps helps to compensate.