Was never a question of safety.
The cycle longevity vs DoD charts consistently show crazy short lifetimes going that low.
Stick to 50% max if you want to get more than a few years from that pricey bank.
DC-DC battery charger under hood?
- Thread starter msand1977
- Start date
The cycle longevity vs DoD charts consistently show crazy short lifetimes going that low.
Stick to 50% max if you want to get more than a few years from that pricey bank.
restorationrides
Member
So why are you referring to small European cars with as you say weak alternators (who needs Banks of batteries for those) when we're talking about banks of batteries for something much larger such as a caravan or RV...?
As far as Caravans and RVs and that sort of thing, they typically have fairly substantial alternators...
Also, why would these vehicles be able to produce much more electricity while braking? Unless you are referring to regenerative braking which is another whole discussion and not something you're going to find on a caravan or RV at this point in time...
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restorationrides
Member
Here's where some of the confusion comes in I think. There is nothing magical that these dc-dc chargers are going to do that an alternator can't do also. I agree with you that moving the batteries closer to the charge source is going to be more efficient and allow you to use smaller wires. But as pointed out by someone else a couple of times now, these dc-to-dc chargers have relatively low output in amps. That is why they allow you to use smaller wires. 12 volts is still 12 volts no matter which source provides it. And keep in mind that what seems to have been forgotten in many of these discussions is that we're really talking about power. The power to charge your batteries. Power (watts) is a function of volts x amps. Another thing to remember is that alternators do not set a particular voltage for the battery to operate at. Rather the 12 volt battery with 6 cells sets the voltage at 12. So if you drive the voltage higher, then the amps required will be reduced (given the same amount of POWER output from the source charger, regardless of the type of charging source that you're using). This can of course be a good thing if you're reducing the amps required to provide a certain amount of power to a battery Bank. NOTE: High amperage at any voltage tends to get things hot and less efficient...
But the minimal DIFFERENCE in voltage that you're talking about between a dc-to-dc charger and the vehicle's alternator that could do the same job, are inconsequential unless you like to contemplate things like "how many angels fit on the head of a pin".
No, I'm fairly certain that these dc-to-dc chargers really fit a very small market. That is, stepping up or stepping down in voltage. Such as from 12 to 24 volts, or 12 to 48. But keep in mind that to go from 12 to 48 volts is going to require four times as much current on the 12 volt side as is going to be realized on the 48-volt side. So if you want to fast charge 48 volt system you're going to need some mondo wires between your 12-volt Bank and your DC to DC charger, and a big powerful and expensive charger that would be.
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AFAIK the discussion is DCDC chargers generally.
Certainly nothing to do with RVs!
In many countries around the world these high-mpg electrical systems are becoming more prevalent, in many cases buying new nothing else is available, including the **van** types many want to convert for camping.
Nothing to do with "small cars" in many markets.
Yes for those with vehicles suitable for conversion to a good alt setup as I outlined, that option can reduce the need for DCDC chargers.
> with cabin mounted batteries you don't need huge wires
Yes that is valid for long runs
> you no longer need a starter isolator
Unless you wire your Alt to House directly )best practice if a good Alt setup) and want to charge your starter from House sources.
> it's an MPPT controller for a solar set up
But not the right unit for all setups.
Stop arguing against a straw man, we are dealing with very low tech science, you're not arguing with the vendors making overstated claims here.
Stock alternator setups on their own just aren't suitable for many setups with large expensive banks where the owner wants to take proper care to ensure longevity.
> these dc-to-dc chargers have relatively low output in amps.
Few alts can feed Sterling's 120A unit's max capacity for long, especially in hot weather, and he's got a 180A version coming.
> alternators do not set a particular voltage for the battery to operate at.
****** is that supposed to even mean? The VR's job is to precisely regulate Absorb voltage to what the bank requires, that is **all** it does!
If you have a nominal 24V or 48V bank to feed, plenty of alt/VR setups out there designed for that, nothing to do with the need for DCDC charging units.
> High amperage at any voltage tends to get things hot and less efficient.
A normal stock setup reduces output as temps climb. Better ones derate amps smoothly, lousy ones drop voltage, in effect stop charging completely.
That is exactly why the precision of a DCDC charger is often required, both to protect alts designed just for propulsion/starter service, and to make best use of that alt's fuzzy output for the health of the bank.
A good large frame alt / VR setup can put out 200A all day long cruising the Simpson or Nullabor plain, no problem. Its output should of course be connected directly to House.
But there are use cases where even after spending thousands on such an upfit, a small cheap DCDC charger is required to keep the Starter batt charged.
> the minimal DIFFERENCE in voltage that you're talking about between a dc-to-dc charger and the vehicle's alternator that could do the same job, are inconsequential
That's your subjective opinion and judgement call. May be perfectly appropriate for **your** rig and values, certainly not relevant to all.
Half a volt can make a **huge** difference to bank longevity, and for banks costing thousands, it's important to get things right.
> No, I'm fairly certain that these dc-to-dc chargers really fit a very small market.
Yes that's true, but relative to which larger one?
For those free camping for extended periods in rigs costing as much as many houses, it's a pretty high percentage.
dwh
Tail-End Charlie
Typical voltage regulated alternators are just simple contant-voltage power supplies.
Alternators have a high voltage potential - the voltage regulator, by managing the field coil (essentially an electrical "clutch"), keeps the voltage within a specified range by turning the alternator on/off.
That voltage range may or may not be ideal for battery charging. Often it isn't, since vehicle "charging systems" are designed to supply contant voltage to the vehicle's electrical system. The only "charging" they normally do is to recharge 1/5 of 1 amp*hour (or less) whenever the vehicle is started.
The voltage is not always steady. The voltage range maintained by the voltage regulator often swings back and forth between the low and high setpoints - for instance, 13.5v-14.5v - as the voltage regulator switches the field coil on and off.
By raising the voltage potential of the supply, the DC-DC charger creates a "constant-current" bulk stage which can often do a better job of bulk charging a battery than the stock voltage-regulated alternator.
This can be true even if the alternator is "rated" to a higher amperage than the DC-DC charger. Most alternator ratings are optimistic. They also all have duty ratings and deratings for heat - and they always get hot.
Lead-acid batteries build up a surface charge fairly quickly, which reduces the voltage potential difference between the power supply and the battery, reducing amperage flow. Again, by raising the voltage potential of the supply, the DC-DC charger can maintain a *steady* flow of amperage.
Often a 20a DC-DC charger can do a better job of charging than a "100a" alternator (which is really only a 50a alternator once temp and duty cycle are accounted for).
But as with everything - it depends. People who have a Toyota with a voltage regulator set to max at 13.9v will certainly see improvement with a DC-DC charger. People with a vehicle equupped with a huge computer controlled alternator that has a PWM regulator and temperature compensation won't need it.
Alternators have a high voltage potential - the voltage regulator, by managing the field coil (essentially an electrical "clutch"), keeps the voltage within a specified range by turning the alternator on/off.
That voltage range may or may not be ideal for battery charging. Often it isn't, since vehicle "charging systems" are designed to supply contant voltage to the vehicle's electrical system. The only "charging" they normally do is to recharge 1/5 of 1 amp*hour (or less) whenever the vehicle is started.
The voltage is not always steady. The voltage range maintained by the voltage regulator often swings back and forth between the low and high setpoints - for instance, 13.5v-14.5v - as the voltage regulator switches the field coil on and off.
By raising the voltage potential of the supply, the DC-DC charger creates a "constant-current" bulk stage which can often do a better job of bulk charging a battery than the stock voltage-regulated alternator.
This can be true even if the alternator is "rated" to a higher amperage than the DC-DC charger. Most alternator ratings are optimistic. They also all have duty ratings and deratings for heat - and they always get hot.
Lead-acid batteries build up a surface charge fairly quickly, which reduces the voltage potential difference between the power supply and the battery, reducing amperage flow. Again, by raising the voltage potential of the supply, the DC-DC charger can maintain a *steady* flow of amperage.
Often a 20a DC-DC charger can do a better job of charging than a "100a" alternator (which is really only a 50a alternator once temp and duty cycle are accounted for).
But as with everything - it depends. People who have a Toyota with a voltage regulator set to max at 13.9v will certainly see improvement with a DC-DC charger. People with a vehicle equupped with a huge computer controlled alternator that has a PWM regulator and temperature compensation won't need it.
restorationrides
Member
For purposes of continuity in the discussion, I am going to address your comments one at a time...
""> alternators do not set a particular voltage for the battery to operate at.""
"****** is that supposed to even mean? The VR's job is to precisely regulate Absorb voltage to what the bank requires, that is **all** it does!"
----------------
What was meant by that is the following... The number of cells in the battery determines it's nominal voltage. Pinning an alternator to that battery's terminals commits it to working within that nominal range 12v/24v/48v... Alternators can work in a wide range of voltages (and can generate AC as well as DC output). It is the VR's job to make sure that the charge profile matches the discharge profile as much as possible...
Most VR schema is not very sophisticated. That is, they will taper the output as the batteries come up to full charge. While there may be some nuanced benefits in considering Max charge to be 13.8v versus 14.2v, I think in the grand scheme of things that's too much detail. As I said before, I think you're talking about how many angels fit on the head of a pin. In the real world, we just need the batteries to stay charged. Nature and physics will take care of the rest pretty well.
Let me explain further... The notion that your actively used battery bank is going to be sitting around waiting for the perfect charge every time there's a bit of a discharge on it... or can absorb discharge and recharge in the perfect profile every time all day...is not very realistic now is it?
But, do not fret! Like all well implemented and mature systems, there is substantial buffer built into today's modern charging circuits...
I have worked on large battery banks in yachts down to very small batteries in jet skis. More important than this picayune voltage discussion, is buying the best of the battery technologies (read AGM/GEL), making sure that all of the wiring and connections are up to snuff, and then making sure the batteries are relatively fully charged at all times.
And, yes, that means having sufficient recharge capacity available at all times to keep those batteries charged despite the unpredictability of any discharge profile...
Regards,
RestorationRides
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DaveInDenver
Middle Income Semi-Redneck
Too much detail only if you consider you may never fully charge or may shorten the life of your battery over time.
Vehicle charging systems have been a compromise of cheap and basic effectiveness. They want to return enough charge without any risk of overcharging, which means for flooded types you get an acceptable performance for the average owner and for AGM you routinely undercharge. For our uses, particularly deep cycling, the stock charging system is usually inadequate or at best just inefficient. It's not designed for the large difference in starting (which it is sensing) and house systems as well as just not doing a decent 3-stage profile.
What you think is unnecessary detail isn't so when the difference between a good profile and barely good enough is 0.1/cell. For example, doing 2.4V/cell (14.4V) in a constant voltage charger will be 4 times as effective as 2.3V/cell (13.8V) because as @dwh has mentioned current is a function of voltage.
This is the primary benefit of a DC-DC charger. You might have 100A available but at 13.8V it's never actually going to be forced at anything near that. You'll probably only be in single digit amps, it's essentially a float or trickle charge. At 14.7V the full 25A will be forced and it doesn't need to run 80 hours to finish.
No, that commitment happens when you purchase an alt.
> Alternators can work in a wide range of voltages (and can generate AC as well as DC output).
No, those quality 12V VRs that allow the user to adjust setpoints may have a range between say 13.1V to 15.6V.
A nominal 24V alt may range between 26.2V and 30.2V).
None lets you select between 12 and 24 ranges from the same set of hardware terminals afaik.
Ability to adjust Hold time of Absorb V before transitioning to Float is also critical.
> It is the VR's job to make sure that the charge profile matches the discharge profile as much as possible
No, what needs matching is the batt mfg spec sheet, and the user's calibration using an ammeter.
"Discharge profile" has no meaning nor relevance, discharge voltages without charging active, are always way lower than charging voltages, and are not regulated by any device, they just vary based on current and SoC.
> Most VR schema is not very sophisticated.
Exactly why, if you don't have a precise VR as above, e.g. Balmar MC-614, it is more likely a DC-DC charger is required.
> That is, they will taper the output as the batteries come up to full charge.
No, a good one will keep a precise CV right up to Full, and only then drop to Float.
If you mean current, trailing amps fall as SoC rises according to batt chemistry, not regulated by any device.
> While there may be some nuanced benefits in considering Max charge to be 13.8v versus 14.2v, I think in the grand scheme of things that's too much detail.
No, with a large quality bank costing thousands, I want to do my best to ensure it lasts as long as possible. A GEL or LFP bank will be quickly murdered if an AGM charge profile is applied, and vice-versa.
Yes old-school FLA is more robust, accepts a wider range, but say you carry a 6S 2000AH bank of Rolls / Surrette 2V cells costing $2000, why would you accept it lasting only five years when they should routinely last a decade or more?
And who wants to have to water their bank on a more frequent schedule?
Plus most importantly, prevention of unexpected failures can be critical in remote foreign locations where access to replacements is difficult and super-expensive. That requires good predictability and control over charging parameters.
There is no reason for your alt system to be any less precise than your mains or solar.
Now, if **you** only deal in cheap banks, or just don't care about bank longevity, say so and we're done debating.
In fact that seems to be the case.
CoyoteThistle
Adventurer
Whew, lively thread! Question for the OP if you're still watching: Have you done any research on an easy way to disable the "smart" part of your alternator?
I have a 2010 Nissan Frontier and I was able to pull a fuse in the fuse box under the hood (labeled Horn/Alt, 20A IIRC) and this turned my alternator in to a nice dumb one putting out a constant 14.4v (but I have no horn now - strange choice in combining these you Nissan engineers). The alternator self-protection still works - I get up to 80amps to the house battery at start up, drops to about 50amps after a couple minutes and settles at about 35 amps until the battery is full. I didn't know any of this would work this way when building my system, my backup plan was a DC/DC charger but I saved a few bucks with some experimentation/research.
Best of luck with it!
I have a 2010 Nissan Frontier and I was able to pull a fuse in the fuse box under the hood (labeled Horn/Alt, 20A IIRC) and this turned my alternator in to a nice dumb one putting out a constant 14.4v (but I have no horn now - strange choice in combining these you Nissan engineers). The alternator self-protection still works - I get up to 80amps to the house battery at start up, drops to about 50amps after a couple minutes and settles at about 35 amps until the battery is full. I didn't know any of this would work this way when building my system, my backup plan was a DC/DC charger but I saved a few bucks with some experimentation/research.
Best of luck with it!
teotwaki
Excelsior!
How you must view yourself
How your message actually appears
How your message actually appears
Mommy! Mommy! He started it first! I just had to be angry and insulting to everyone who disagrees with me!! Not my fault!!
teotwaki
Excelsior!
I liked the one point made a few posts back where this might be addressed by using an DC-AC inverter, running the ac lines the 35' and then using a commercial battery charger on the batteries.
DaveInDenver
Middle Income Semi-Redneck
Was that in this thread or another? I dunno. The potential downsides are some slight conversion loss (very manageable, a few percent) and the non-trivial need to make sure you don't shock anyone (also manageable with good workmanship).