dc dc converters/chargers for batteries?

Forgive me - my first ever "New Post" - I am rarely an OP (this is my first on 12volt). This may be more applicable to RTV, 4WD and camping forums/situations, but.... How common is it to use dc-dc converters or dc-dc "chargers" for charging "other" batteries in a vehicle? EG - to boost the alternator voltage to (say) 14.4V to charge auxiliary batteries elsewhere in the vehicle. All that follows hereunder is ramble & FYI & LOL so feel free to skip.... I know it's a valid and great technique - certainly where voltage drops to the 2nd (or other) batteries are much higher than to the main battery. But I'd prefer to minimise the voltage drop etc etc, and ensure maximum alternator voltage (ie, to supply 14.4V at the main battery). The reason I ask is that a mate recently returned after a long absence. (He has been overseas long enough to forget our culture and accent!) Planning a trip to our remote outback, he got involved in a local forum. (No - he didn't heed my warnings about Aussie forums. And he's lost touch with Australian "tall poppy" bashings LOL!) Some were very keen to push dc-dc "charges" for secondary batteries. Whilst like me he knows their merits, he considers upwards of $300 an exorbitant price to pay - especially since in his experience, it's usually alternator and distribution undersizing that is the core problem, else alternator under-voltage.    Under-voltage is usually easily fixed (eg, diodes in the Sense line) and cable (distribution) losses should be overcome - especially if merely for battery charging. (Voltage drops under high loads may be difficult, but to use a dc-dc converter to supply hi-power amplifiers etc? And typical loads like fridges etc are usually under 10 Amps.)    And nothing fixes an under-powered alternator. (Unless maybe these converters magically create power?) (LOL!!) Yet these people seem to push the converters (or "chargers" as he was corrected to...) as the simple fix. No if any mention of the Big 3 or other simple basics. And though he suspect the site as being a good front for pushing products, he was keen on my views etc. But I have rarely seen them used. Most I know would not want such an expensive solution that requires specific hardware - they want simple readily available components that do not add their own inefficiencies and reliability issues - especially when the application is so limited (ie, only when mobile; they would solar-charge or move batteries when stationary etc). Hence my question - in your (non-Australian) experience, is it common for people to fit expensive dc-dc converters to overcome distribution losses etc? FYI - he pointed out that his alternator charges at 14.4V (at the main battery) and his main battery initially charges at about 40A after cranking. Hence, if this battery were to be remote, it would require a 40A converter to equal the rate of charge. That's expensive! He doesn't think the pushers understand his point that an example 8A converter would take 5 times longer (sort of) and that by the time it did, the battery is reasonably full anyhow (ie, after ~1-2 minutes, his battery isn't far above its float or fully charge current). He has already witnessed one replier that consistently criticised his battery isolation switch (a charge-light controlled relay) as not supplying as many AH (yes, Amp-Hours) as a particular "smart" isolation switch. That replier never answered how his 80A isolation switch provided more AH(sic) than my mate's 140A relay, but it turned out that replier was the designer and manufacturer of said isolation switch. Maybe he was baffled by his own advertising blurb? Anyhow, despite his suspicions, my mate insists on behaving like me and others on this forum (like I'mAnIdiot) by checking his knowledge... I wonder how long before he comes over to 12volt... ha ha! (I've only been seriously tall-poppied once, and even that was not on here... mp3...)

Nothing is 100% efficient. If you convert a flat 12v DC to a higher DC, then you must use a current to voltage converter.

While it's true that you get 14.5v output to charge a secondary battery, you do this at the expense of the battery you draw from, which in turn has to be recharged from the alternator.

There's no free ride here.

If your main battery not only supplies most of the essential electrical requirements of a moter home, but also requires 40A draw to charge, it seems silly to me to continue to tax it.

YOU CAN GET the voltage from the alternator to anywhere in a vehicle you want to, and add a seconday alternator a lot of times.

An isolation switch has a purpose when used correctly, however I wouldnt listen to cheeky advice from folks who are pushing their wares.

I know just enough to be dangerous. VERY dangerous.

He knows all that, and he assumes they aren't THAT stupid (after all, they aren't EFI hackers...) But assuming that the alternator has spare capacity and it is merely a case of too high a voltage drop from the alternator (supplying 14.4V to the front battery) to the "rear" battery - maybe because the rear circuit is supplying a large load. So.... Who uses a dc-dc converter - ooops... sorry, CHARGER! - to overcome that? I'm not into the why and wherefores - that's for the dikheds - sorry, innocent-until-proven-otherwise libelous pushers to justify later. At the moment he just wants to see who uses capacito... er, dc-dc con's in these situations.    [ This dude is no fool - but I may be somewhat biased - we have come to share many things that still appear magic to others. (I lampooned a few posts & forums and recent events; he reciprocated with his experiences. I beat him wrt cretanic audiences; he beat me wrt cranial vacuums in "high" places.) ] We both know there are justifications - eg, topping up an "fixed" battery or an excessively discharged battery from a full one (at the expense of overall energy loss - but simply to preserve battery life); or where the supplied power is wasted due to low voltage - ie, battery charging (all be that more like solar panel where nothing can be done about the voltage range other than use MPPTs etc). But like him, I suspect they are pushing their snake oil (to use a term a pusher used in a recent post - even though he was referring to cheap simple solution....!). I mentioned the pusher that kept retorting with bullsh about how his non-converting voltage sensing isolation switch would supply more Amp-Hours to battery than my classic charge-lamp controlled relay (which my mate also uses - like I said, he ain't stupid!) even though I quoted a 140A relay to his 80A isolator. Later came comments about its difficulty (finding the charge-light wire) and "all the extra wiring" compared to even an ignition-controlled "isolation switch" (LOL - it's the same except my version is usually local to the alternator-battery. And that wire is the only additional wire compared to a voltage-sensing isolation switch.) So that's the level of hype he is dealing with. Although he too rejects zero-tolerance policies, he has adopted my 3-strikes attitude - so he may not last long enough for this issue LOL! (As I told him, with help like that, I'd rather take my chances outback!) I ramble, but hopefully you get the feel. NO COMMENTS OR EXPLANATIONS are needed - merely the metrics - like how common... (That's for starters; maybe by whom for what etc.) But having said that, ohhhh! it feels so good having someone confirm the obvious. (Not that I would ever deliberately seek to endorse nor concur nor compliment your opinions Anonymous exalted one.) In fact, maybe short endorsements like "good idea" or "fracken mtheads" etc are welcome - especially if dc-dc con's are not commonly used OT (Over There). Remember - I come from a forum-place where the solution for a >1000W RMS amp off a 45A alternator was or is to get a bigger battery (or two) - and maybe a cap for good measure... Yes - it's true what they say about Australians - we kill things. (Maybe the original quote was "... they shoot things don't they?" But firearms were banned... Nonetheless, we have our means.)

Hehe yeah, you know I'm either over-stating the obvious or preaching to other choir where-as you're concerned. And if I reply to you about stuff you know all to well, it's largely rhetorical.

It's all magic and smoke and mirrors anyway right?

I know just enough to be dangerous. VERY dangerous.

The blurb is smoke & mirrors - yes. That's the snake oil. But like the term "quack", many terms have been inverted (reflected? LOL) and are now being used by the people they were originally directed against. It's like terror -> terror-ific -> terrific. Sick on the other hand is grouse. But I love your rhetoric (as above etc). It is good for others to read (IMO). And it consoles - else alerts - me. In this case it made me see that others' comments - as in short crits else endorsements - should also be posted. (Especially since so far there are no "formal metrics"... Cool - I can report back that no-one outside of Australia had admitted to knowing any dc-dc charger installations for "rear" batteries (etc).) But I did want to prevent people spending time discussing the pro's and (obvious) cons. Besides, I think the "snake charmers" should educate us. I'll post the link if it gets to that. We all love a bit of a laugh, though I find things like usually depressing. The site is free as a "registered guest" so you can post replies. It only costs AUD$60 (per annum??) to become a member so you can.... er, ... PM other members, and get discounts (like a GPS holder for $69 - I bought the same for $89 but mine included a GPS).    BTW - my mate likes this site too. "It has its incidents, buy yo those guys are good..." Yep - maybe I'm a tad biased.....

Well, the responses have been so overwhelming! So dc-dc chargers are so popular? Or is it just this site? But hot off my press - products like the CTEK D250S for a special price of AUD$370! That's for a WHOPPING 20A dc-dc converter (with 3-stage battery charging)! Compare that to buying a 2nd alternator - eg, 250A for the same price or cheaper. (I stress - we are discussing in-vehicle "boosters" and "chargers" for "remote" batteries.) You can download the pdf blurb at ctek.com-D250S_Flyer_UK_low.pdf Alas my poor mate is having a hard time. He thought Australia's "Brain Drain" referred to people like him that went overseas. He is now considering testing what is in our water supplies and air! He thought maybe it's just that particular site and its "old gullible" grey nomadic audience, but he too realises that it's the elders that are usually LESS gullible to such quaff - especially those with the travel mindset. (He does me proud for one so young!) But he's off-site for some hours caring for some sod out of hospital and he's accused of doing a gutless disappearing act. But he has seen Aussie posts from a similar sufferer. I even showed him my recent mp3car experience where the interjector removed all his posts! (Why? He responded that he didn't like my attitude. He didn't like interjecting, posting wrong information, and being corrected??) My poor mate. He really has lost touch with our tall-poppy syndrome. But he too is seeing the typical denial, transference, & ridicule cycle. (I hate boring predictability!) He has also started recurring work-related dreams. I wonder why? But he is sleeping peacefully at the moment..... I looked at some (of his) recent postings and whilst I've been saying Aussies have an advantage in that many (older) alternators are 2 or 3 wire (unlike the USA-popular one-wire D+), his site and others claim alternators can never fully charge a battery else cannot charge it properly! (At least the above dc-dc converters/chargers are 20A - a reasonable current for charging a severely discharged battery - hence requiring a pro-charger else an alternator.) Some of this is directed at the alleged "float voltage" of alternators (despite Bosch accounting for ~60% of Australian alternators, and they are usually set to 14.2 or 14.4V). I think my typical $1 voltage boosting methods are slightly better than inefficient $200-$400 solutions. Even if boosted above 14.4V for "remote" batteries, a main system/battery throttle or disconnect still seems cheaper (a PWM MOSFET or two....). Of course one could "create" more energy with a second alternator for the remote battery.... Or imagine running the remote heavy loads off one feed, and having a dedicated cable to provide 14.4V to the remote battery (from the main alternator - move the causal remote-load's voltage drop to another cable). Cheaper and more efficient than a $xxx converter? Nah - you can't fool those dudes. They realise how much longer a vehicle battery will last if it is dc-dc converted - after all, I only get 6-8 years from my alternator-charged batteries (mind you, I only converted inbuilt regulators about 2 years ago). These dudes no doubt have the results to prove it - just like those Capacitor manufacturers & retailers, and Optima's results for the paralleling their batteries etc. (Speaking of which, one inquirer asked what my mate had against paralleling "matched" batteries. He's already been through the same temp, same interconnect cabling and diagonal tap scenario. He's a bit sick (already!) of "the big hand is on... & the little hand is on... when our bush pilots merely want to know if it's Saturday. Or Sunday (so they can land). Anyhow, maybe I should broaden my original inquiry? (Though I suspect many here consider it the same as I consider "his" sites & threads - not even worth replying to.) But give me something good.... I need an excuse to wake him! (We live in a country where - according to our former Foreign Minister - "sleep deprivation" is NOT a form of torture. He's allegedly educated but obviously can't read Swiss. If only they spoke a more common language in Geneva. But what would foreigners know anyhow?!) Again I apologise for my rant, but this has been somewhat involving.... (3 Monkeys) But to quote a prominant politician (the current Opposition Leader) - people here choose to be mislead (or stupid, or poor, etc). I guess that is the benefit of our free society. I just wish it were as cheap as the USA - we adopted their philosophies yet not their prices!

I smacked my (former?) Mate this morning. He's arguing that some dude is describing 2 parallel batteries via fuses between bussbars to loads or charger as a Wheatstone Bridge where the voltage drop across the fuses is the same yet "you can measure" a voltage drop between the batteries. I'm thinking that he's having one of my "the over-current LED string robs current from the other parallel strings" moments. But this is great - you can't delete posts from this other forum! Got the dude!        Ka-Chang! I say 4 words. "You (...) idiot". That's 2 words, the you is implicit in the (...). Duh? "Passive!" Light's on, but nobody's home... "Floating!" D'oh No! But we were discussing.... Yes dear Laze & Gems, the Wheatstone Bridge being 2 batteries (bottom) with 2 fuses (top) and a Voltmeter in between is floating. It is not powering any load, nor being charged. Hence the +ve bussbar is at the mid-potential of the batteries and the fuses have equal current - exactly as the battery salesperson wrote. Salesman 1. Mate zero. But I understand. He's already seen some "amazing" statements... Mate is concentrating on his normal parallel systems - either charging or discharging, but never idling. He is picturing his battery impedance measuring networks for condition reports. He is picturing infra-red monitoring for cell & block problems. Along comes a salesman saying batteries can be paralleled without qualification. Even says a failed cell is not a problem.... The monitoring (wheatstone) later added after Mate's quizzing... What a crack up! I don't think Mate even fully qualified his stance - ie, don't parallel unless charging or (specifically) discharging, unless monitoring in place. A bad slip. He is thrown by references to internal resistances - which in restrospect is relevant, but wasn't for the loaded/charging situation.... And you can parallel matched batteries, but as soon as f.ex a cell collapses, they are unmatched. (Hence paralleling no longer covered by warranty?)     And the patronising - ESR is dynamic you know; wheatstone; give you a clue; & more LOL. Worse though, it seem readers have been upset and complained to the Mods. His apology was interrupted by a callout, but I'm so looking forward to it LOL! Hopefully tomorrow or next.... Meanwhile.... This thread closed.   (The original issue anyhow... and obsessions )