Charging AGM battery located in cargo bay

[Rock Trol]

Greetings all,

Last weekend I was at the Caravan and Camping show in Adelaide when I dropped in to one of the display stalls from a company that manufactures very expensive AGM battery packs. I wont mention which one but they are made here in SA. I started talking to one of the staff and we got onto the topic of in car charging. He was not a fan of BC:DC battery chargers and thought they where not good for AGM batteries. OK for Calcium and when voltage drops but he said that they don't recommend them for their battery packs. Just let the alternator do the job with a good bit of wiring.

I am in the process of relocating the battery at the back and I already have a Redarc BCDC 1220 charger. Cabling is 6 gauge (125 amp) to the rear already so it wont cost me any extra to set the battery up in either configuration. I am not sure why they are against the dc2dc battery chargers. The company in question has been around for quite a while and specialises in 12 volt automotive gear. Outdated opinions? Who knows?

I could also set it up to use both methods via Anderson plugs if there is an advantage.

[the evil twin]

I pretty much agree with him esp if you have 6 AWG wiring.

Not all that much point in a DC/DC Charger if you are seeing 13.8 or better at the Aux

[Cuppa]

If the BCDC 1220 has the same float voltage as the BCDC1240 (13.3v) this may be the reason, as most AGM manufacturers specify 13.6v -13.8v float. My Ritar AGM’s are recommended to have a 13.8v float voltage. However I’ve had them on the BDC1240 since day one, over 4 years. The vehicle sits in a dark shed for much of the time, & the rested battery voltage is usually at 12.6v or 12.7v. The BCDC pushes in a brief bulk charge & then drops them into float mode within a few minutes of starting the car. As far as I’m concerned all is as it should be & having a lower float voltage is of no real consequence. I can’t think of any other reason why they wouldn’t like dc to dc chargers. Calcium requires a higher charging rate than AGM’s so what you were told doesn’t make sense to me, as the BCDC can set the charging rate at 14.4v that AGM’s like. It does *very* briefly flicker between 14.5v & 15v immediately before dropping back to float voltage, but the length of time it does this for is so short it really is of no concern.

EDIT.
There are arguments about whether dc to dc chargers are necessary or not. My view is that their usefulness is determined by 2 things ..... to compensate for voltage drop in long/thin cable - not a concern for you, & to ensure the battery is brought up to 100% in as short a driving time as possible. (That way you have more available capacity when arriving at camp). 14.4v & smart charging will achieve this better than 13.8v & no smart charger. However if the battery is discharged to low levels, bulk charge from the alternator will bring it up to 80% - 85% more quickly. I tend not to discharge my batteries to the extent that this is an issue for me, BUT, I do have a manual override to allow direct bulk charging if I ever do .

[Rock Trol]

Thanks guys. I see the same voltage at the rear of the car and in the engine bay so there isn't any noticeable voltage drop. The alternator does drop down to 13.5-13.6 after a while though. I assume its because the batteries are charged up and maybe engine temps have risen.

I have plenty of 8 AWG wire left over from another project so I might run it from the 6AWG to where the battery is located and put an Anderson plug on it. Then set the charger up with Andersons as well so that I can plug it in or unplug it when I want to. Not sure why that guy was so against them as they way they are supposed to work makes sense. I guess both methods will work though. His view is definitely held by a minority of people as far as I can see in the internet.

[sooty_10]

Really it is simply an added unneccesary expense (dcdc) if you use appropriate wiring an alternator will do the job for most 4x4's (my opinion). The main advantage is the ability to have long wire runs to a camper and still achieve sufficient smart controlled charging without the need for large heavy and expensive cables to combat the voltage drop.

Usually batteries in campers sit around for a while (in sheds or camp sites) and need a bit more smarts to maintain them as close to 100%, batteries in cars are less likely to be discharged as heavily as a camper/caravan setup. There is a point where the practicality of one begins to out way the other and thats why everyone has different setups (also different opinions as youve noticed).

Also for modern cars with low voltage alternators dcdc wins hands down. If your happy with how your dcdc system is performing and it works for you problem solved. No need to go reinventing your setup.

Another reason I'd look at going a dcdc over my current alternator setup would be if I had a large aux battery bank (eg. 2 or more large capacity deep cycles) which I didn't want to link at all and ?? potentially increase my main/starter charging time. And by keeping the two battery banks eg car / camper separate if one drops cells or doesn't hold charge it won't pull down your other bank.

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[Rock Trol]

Thanks sooty. I will wire the redarc back in since I already have it here.