Using an automotive battery charger when onboard fails

[opnspaces]

Many times we see posts here about somebody experiencing a failed built in battery charger while out on vacation. Invariably we suggest buying or using a cheap automotive battery charger to keep the RV running until they can get home and replace the failed unit.

My question is, can any newer, automatic battery charger be used for to keep the coach 12 volt running? Or does a person need to look for a cheaper (possibly something from Harbor Freight) charger?

[K_and_I]

landyacht318 wrote:


Usually thegreen light means the charger has stopped applying 14.x volts. It might either completely shut off, or hold a 'float' voltage which on a flooded battery is around 13.2v at 77f and 13.6v on an AGM at 77f with a few variances depending on manufacturer.

The ammeters on chese chargers are not to be trusted without confirming it, and like most 'smart' chargers will actually stop absorption voltage before the battery is indeed full.

Charging does still occur at float voltage, but at a very tiny rate as the electrical pressure is so low.

So voltage tells only part of the story, how much amperage is flowing at that voltage tells nearly all of it. Unfortunately, I have found on the three different chargers that have their own needle analog type of ammeters, to be generally representative of current high vs low but nowhere near the actual numbers printed along the bottom when tested with a known to be accurate DC clampmeter or an inline shunted wattmeter and often, both.


Good enough for most starter battery/garage applications, and any charging is better than no charging, but the regularly cycled lead acid battery craves the true full charge applied regularly, and plugging in for many hours with a charging source incapable of achieving the true full charge, just ain't right.

The key to reaching true full charge is holding the battery at high enough voltage for long enough, and no longer. Few automatic chargers do a good job at even approaching this ideal.

The inability of chargers to hold high enough voltage for long enough to truly fully charge a hard working deeply cycling battery, has had some of us resort to adjustable voltage power supplies that seek and hold a chosen voltage until turned off, by a human or a timer set by a human.

I have achieved a nearly unbelievable amount of deep cycles from my current AGM battery by insuring I can get it truly full, often, and I take it well below 50% state of charge, often.

PM sent.

[joebedford]

My 100A WFCO failed at 2 years minus one day (2 year warranty). They replaced it no questions asked. Thought about changing it out for a better quality converter - it's now 6 years later and I'm still thinking. Used a 10A Schumacher for a week without problem.

[MEXICOWANDERER]

The only mode I would utilize is the manual voltage adjustable one and for a bit less money I can get a Meanwell RSP 150 ampere unit. It loves a strong generator and there are 9 fixed chick-click-click voltage settings and a 12-hour timer...

For this PORTABLE battery CHARGER.

And voltage settings determined by a battery design engineer, and not a computer chip programmer in Uttar Pradesh India.

For AGM one setting maintains 14.40 volts exactly. There is a 16.00-volt current-limited circuit for equalization done correctly.

Every wire inside and there is a bundle of them is SILICONE tinned. And there are 9 Bournes TWENTY FIVE TURN pots in the event one of the voltage steps needs to be tweaked. This is an expensive labor-intensive effort that makes the BORG and Hyperwatt projects look like child's play. Yeah the controls are all Mil-Spec.

[BFL13]

"Aren't thoust the one that said that particular CONVERTER/charger the Power Max is no longer available?"

Not understood. The above photo shows three Vector smart chargers with the follow on Black and Decker version of their 40 amper. These are indeed no longer available, more's the pity.

You can get the PowerMax converters anytime-- the 60 amper PM3-LK is about right for many RVs with two batteries and a 2000w gen.

https://powermaxconverters.com/product-category/converters-ac-dc/

[MEXICOWANDERER]

Ohhhhhh Seeeeeen-yore!
Aren't thoust the one that said that particular CONVERTER/charger the Power Max is no longer available?

Remember the word Meanwell or Megawatt? They are cheaper than Mattel Playtoys. They are ideal for use with generators unless of course a person forgets and lets them charge for a couple of weeks

(Sarcasm)

Long ago on this forum, someone posted a timeline of different voltages and time at each voltage value to recharge a battery.

If a camper boondocks for a few weeks then returns home and plugs in for a few thousand hours a Mattel charge will slow down the capacity loss due to chronic sulfation.

The key is battery lifespan. Camping off-grid for one week a year really does not tax a battery. Boondocking 60 days a year really separates the wheat from the chaff. I went through an average of 260 hours daily with 38 cubic ft of refrigerator and freezer. This is at 24-volts. But Quicksilver has a 400 amp alternator. It charges 400 amps at a dead idle. I use a 50-amp rectifier to bias the voltage regulator sense lead when parked so voltage jumps six-tenths of a volt.

But I use 2 Megawatts on the banks when I get home.

[BFL13]

MEXICOWANDERER wrote:
You describe an old MANUAL charger without timer. They are not allowed to be sold anymore in too many states.

For shorter excursions, a smart battery charger will wheeze out just enough power to limp by. For top charging or restoring a full charge, they are as useless as **** on a boar hog. Try to opt for a pay-for added guarantee on a smart charger. Then all you will be stuck for is the shipping costs when it ignites or plays dead.

Chargers that do not have a built-in timer are extremely stupid. And anything that claims to be automatic or smart is NOT a battery charger -- it is a Tickle Me Elmo grade joke.

I do not agree. A particular battery charger does what it does. It is a tool. "Use the right tool for the job." The chargers Mex hates so much are not all the same for the same jobs, but they are not all suitable for each part of the "charging profile" to bring a battery from 50% to 100%.

Many portable smart chargers are "just fine" for doing 50-90s while camping. Many do not have enough amps, so they require too much gen time to do a 50-90, but you can use more than one at a time to add their amps.

Getting a battery from 90 to 100 or even from 97 (when many automatic chargers shut down) to 100 requires a different sort of charger. A different tool to do that job.

Finding a charger that will do it all, no matter what the job is, with enough amps to do it by itself, is close to impossible. (PowerMax adjustable voltage LK models come close though). You might have to use one charger for one part of the job and another for another part of the job.

If you try to use the wrong tool for the job, then of course the only thing to do is blame the tool! 🙂

These are not "tickle-me Elmo" chargers for instance: (add up their amps as shown and that total is what was showing on the Trimetric as going into the battery bank --maxing out a Honda EU3000is)

[landyacht318]

4x4van wrote:

Interesting. So you're saying that even though the amperage tapers down on the charger, the voltage stays high, and could push the actual battery voltage way above safe levels if left on too long? I have in fact left my charger hooked up overnight AFTER the meter has tapered down to zero and the green "battery charged" LED comes on, but I've never actually checked the voltage that the charger is putting out, neither when first hooked up nor after it has tapered down; guess that's something to put on my "to do" list next time I need to use the charger.:C

Usually thegreen light means the charger has stopped applying 14.x volts. It might either completely shut off, or hold a 'float' voltage which on a flooded battery is around 13.2v at 77f and 13.6v on an AGM at 77f with a few variances depending on manufacturer.

The ammeters on chese chargers are not to be trusted without confirming it, and like most 'smart' chargers will actually stop absorption voltage before the battery is indeed full.

Charging does still occur at float voltage, but at a very tiny rate as the electrical pressure is so low.

So voltage tells only part of the story, how much amperage is flowing at that voltage tells nearly all of it. Unfortunately, I have found on the three different chargers that have their own needle analog type of ammeters, to be generally representative of current high vs low but nowhere near the actual numbers printed along the bottom when tested with a known to be accurate DC clampmeter or an inline shunted wattmeter and often, both.


Good enough for most starter battery/garage applications, and any charging is better than no charging, but the regularly cycled lead acid battery craves the true full charge applied regularly, and plugging in for many hours with a charging source incapable of achieving the true full charge, just ain't right.

The key to reaching true full charge is holding the battery at high enough voltage for long enough, and no longer. Few automatic chargers do a good job at even approaching this ideal.

The inability of chargers to hold high enough voltage for long enough to truly fully charge a hard working deeply cycling battery, has had some of us resort to adjustable voltage power supplies that seek and hold a chosen voltage until turned off, by a human or a timer set by a human.

I have achieved a nearly unbelievable amount of deep cycles from my current AGM battery by insuring I can get it truly full, often, and I take it well below 50% state of charge, often.

[MEXICOWANDERER]

You describe an old MANUAL charger without timer. They are not allowed to be sold anymore in too many states.

For shorter excursions, a smart battery charger will wheeze out just enough power to limp by. For top charging or restoring a full charge, they are as useless as **** on a boar hog. Try to opt for a pay-for added guarantee on a smart charger. Then all you will be stuck for is the shipping costs when it ignites or plays dead.

Chargers that do not have a built-in timer are extremely stupid. And anything that claims to be automatic or smart is NOT a battery charger -- it is a Tickle Me Elmo grade joke.

[4x4van]

landyacht318 wrote:

4x4van wrote:
My cheap HF charger (2/10/50 Amp) tapers down the charge amperage as the battery SOC increases. I've never used it in an RV for an emergency power supply, but wouldn't be worried about it overcharging. Not sure why I would need a "timer", as it automatically ramps down to just a trickle charge.

This statement reveals an incomplete understanding of how batteries charge or how battery chargers work.

The charger has a maximum allowed voltage.

As the battery nears full charge it requires less and less amperage to maintain that maximum voltage. This is called constant voltage stage or absorption, whereas the time before battery voltage has reached that plateau is called bulk, and is a constant current stage.

Float stage applies just enough amperage to maintain a lesser voltage that will not overcharge the battery. Most garage 'smart' chargers in float stage will have a hissy fit if the current required to hold float voltage, or absorption voltage varies, and it will vary if someone is inside turning DC items on and off.

So yes, the charger ramps down the current, but not because it senses the battery is nearing full, it simply is ramping down as it it trying to prevent the voltage from going higher than the maximum allowed. If the current were constant, not allowed to taper, then battery voltage would keep rising, and 12 amps constant on an otherwise healthy group 31 flooded battery can likely push voltage up into the 17's in just a few hours after current would have started tapering had voltage been capped at 14.7v.

All the while the battery fizzes up a storm, smells of sulfur burps and spews electrolyte, and begins heating up rapidly in thermal runaway. Those Giuant wheeled chargers at auto repair joints from 20 years ago can easily accomplish this if they are left on for too long.

As to when a charger shuts off, well this amount of time it holds absorption voltage, is a guess, as every battery will be different and change as they age, so the time in which to hold absorption voltage is a big guess, with a large lean toward safe, which means undercharging as overcharging can be dangerous.

The battery that has a chance to actually achieve full charge, but is not allowed the time to do so by a 'safe' charging source, is like getting kicked in the balls right before climax.

The chargers which insist that amperage taper to such and such a level before dropping to float, when used as a power supply in an RV powering loads, might possibly keep the battery at 14.7ish volts long after it is fully charged, so NOT worrying about it overcharging in such a task, could be unwise.

How much effect it will have on the battery if this is to occur, is highly variable, if the battery is sulfated then the prolonged time at 14.7ish volts could be beneficial. If it is healthy and then held at 14.7 for many many hours afterwards it is being overcharged, using water, and shedding positive plate material.

Anybody using a regular car charger as a power supply would be quite foolish to not monitor battery terminal voltage initially and then later on, and every so often thereafter. That is if the charger remains on and does not shut off thinking something is wrong.

Never assume it will be 'just fine', unless you have experience with that specific charger in the same specific usage on a battery at and battery capacity at nearly the same state of health.

'Just fine' could be uttered a few seconds before something is just about to fail, without any tools or data or previous experience doing the same thing with similar variables to make such a declaration.

I equate proclamations of 'just fine', in most cases, to be words uttered by the deliberately and proudly ignorant.

Interesting. So you're saying that even though the amperage tapers down on the charger, the voltage stays high, and could push the actual battery voltage way above safe levels if left on too long? I have in fact left my charger hooked up overnight AFTER the meter has tapered down to zero and the green "battery charged" LED comes on, but I've never actually checked the voltage that the charger is putting out, neither when first hooked up nor after it has tapered down; guess that's something to put on my "to do" list next time I need to use the charger.:C

[MEXICOWANDERER]

Lemme get to a Harbor Freight Store and a decal maker.

M.I.T. brand Horizontalator Charger that imparts a polarized magnetic interface that is absorbed like a miracle into the battery. it's STUNNING. It delivers more amps exiting than incoming. Red Green And Yellow Brainiac lights that you can see from a distance.

(I cannot go on, someone will ask where they can buy one. Oh my gut muscles)

[time2roll]

Lot of puffery and doomsday advice when the question is how to get through a few days with a failed converter. A portable has worked "just fine" for many people to avoid trip interruption.

[MEXICOWANDERER]

It's the capacity and lifespan loss that leaves too many clueless folks baffled. But they'll rut anyway. "But I have an Einstien model battery charger!"

[landyacht318]

4x4van wrote:
My cheap HF charger (2/10/50 Amp) tapers down the charge amperage as the battery SOC increases. I've never used it in an RV for an emergency power supply, but wouldn't be worried about it overcharging. Not sure why I would need a "timer", as it automatically ramps down to just a trickle charge.

This statement reveals an incomplete understanding of how batteries charge or how battery chargers work.

The charger has a maximum allowed voltage.

As the battery nears full charge it requires less and less amperage to maintain that maximum voltage. This is called constant voltage stage or absorption, whereas the time before battery voltage has reached that plateau is called bulk, and is a constant current stage.

Float stage applies just enough amperage to maintain a lesser voltage that will not overcharge the battery. Most garage 'smart' chargers in float stage will have a hissy fit if the current required to hold float voltage, or absorption voltage varies, and it will vary if someone is inside turning DC items on and off.

So yes, the charger ramps down the current, but not because it senses the battery is nearing full, it simply is ramping down as it it trying to prevent the voltage from going higher than the maximum allowed. If the current were constant, not allowed to taper, then battery voltage would keep rising, and 12 amps constant on an otherwise healthy group 31 flooded battery can likely push voltage up into the 17's in just a few hours after current would have started tapering had voltage been capped at 14.7v.

All the while the battery fizzes up a storm, smells of sulfur burps and spews electrolyte, and begins heating up rapidly in thermal runaway. Those Giuant wheeled chargers at auto repair joints from 20 years ago can easily accomplish this if they are left on for too long.

As to when a charger shuts off, well this amount of time it holds absorption voltage, is a guess, as every battery will be different and change as they age, so the time in which to hold absorption voltage is a big guess, with a large lean toward safe, which means undercharging as overcharging can be dangerous.

The battery that has a chance to actually achieve full charge, but is not allowed the time to do so by a 'safe' charging source, is like getting kicked in the balls right before climax.

The chargers which insist that amperage taper to such and such a level before dropping to float, when used as a power supply in an RV powering loads, might possibly keep the battery at 14.7ish volts long after it is fully charged, so NOT worrying about it overcharging in such a task, could be unwise.

How much effect it will have on the battery if this is to occur, is highly variable, if the battery is sulfated then the prolonged time at 14.7ish volts could be beneficial. If it is healthy and then held at 14.7 for many many hours afterwards it is being overcharged, using water, and shedding positive plate material.

Anybody using a regular car charger as a power supply would be quite foolish to not monitor battery terminal voltage initially and then later on, and every so often thereafter. That is if the charger remains on and does not shut off thinking something is wrong.

Never assume it will be 'just fine', unless you have experience with that specific charger in the same specific usage on a battery at and battery capacity at nearly the same state of health.

'Just fine' could be uttered a few seconds before something is just about to fail, without any tools or data or previous experience doing the same thing with similar variables to make such a declaration.

I equate proclamations of 'just fine', in most cases, to be words uttered by the deliberately and proudly ignorant.

[MEXICOWANDERER]

Me too. Great supermarket prices and promotions then I get the hell out.