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My UPS is charging my 75AH Car battery

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Yes,

The battery of my car died today. I dont have a clue why but everything was dead as shit. I am lucky that the battery of the car is in the trunk and not the hood, since the key only unlocks the trunk. I removed it, attached it onto my UPS and it's slowly charging right now.

D65C548B-E73F-43FA-8ACE-AB109A69B475.JPG


I think the charging current is around 700mah, it's a 650VA UPS. All i need is like 10Amps put into the battery for the car to start again (and let the alternator do the rest). But does the charging just stop at a certain voltage ? Or a certain current? Or will it continue untill it runs into oblivion?

I will polish the connectors afterwards with a metal brush, to make sure the contact are properly. I prefer having it fully charged and the light is currently blinking indicating it's charging. But i think it will stop at a certain voltage, correct?
 
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I don't imagine that dainty UPS battery is going to do much for you.

Ever consider investing in like, a AC car battery charger?

Anyways no, if you direct wired it, it won't "stop". The voltages will just eventually meet in the middle between both cells, somewhere. It might be just enough, but I doubt it.

EDIT: Oof, I am not a good reader. You are using the UPS charging circuit!

It will push the battery up to whatever the UPS bus voltage is. That COULD be dangerously high for your battery. I'd take it off if it goes over 13.5v or so.
 
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The UPS battery is still inside the casing, just detached from it's mains. It's a 7A 13.8V or so.

So it's charing based on voltage and not current.
 
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The UPS battery is still inside the casing, just detached from it's mains. It's a 7A 13.8V or so.

So it's charing based on voltage and not current.
Realized that lol. Thought I had to be understanding something wrong and whatya know, was right!
 
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I don't imagine that dainty UPS battery is going to do much for you.

Ever consider investing in like, a AC car battery charger?

Anyways no, if you direct wired it, it won't "stop". The voltages will just eventually meet in the middle between both cells, somewhere. It might be just enough, but I doubt it.

EDIT: Oof, I am not a good reader. You are using the UPS charging circuit!

It will push the battery up to whatever the UPS bus voltage is. That COULD be dangerously high for your battery. I'd take it off if it goes over 13.5v or so.
Lead acid batteries are usually charged to 14,4V (thats the cutoff voltage). So no, charging over 13,5v won't blow up the battery. Pb is pretty tolerant to overcharging (much more than li-ion for example) but obviously you'd want some control over how much you charge.

In OPs case, it's going to be fine. I wouldn't leave this setup for days, but a 15-20h charge will be fine.
But since the battery is flat, it's certainly on it's way out. Starter type batteries _really_ dont like to get fully discharged.
Charge the battery and get a new one.
 
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So no, charging over 13,5v won't blow up the battery.
Nope, but I figured the other common UPS bus voltage over that (24V) would. The cutoff was somewhat arbitrary, really. ;)
 
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Car battery can sustain even up to 14.5V. Happens when you drive a car as well. The alternater is constantly switching in between various RPM's thus varying voltages. A charging controller inside the car or alternator makes sure the voltage is evened out for that matter. Some folks even charge their 12V battery with a 24V charger. It's possible, but just dont leave it on there too long.

I was just wondering if the 700mah (it takes longer, days even) was capable of Fully charging the 75AH thats marked on the battery. If i directly hook up the wire from and to the extra UPS battery the wires really get hot, i suspect that one battery is charging up the other and current is flowing through those wires like crazy.
 
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If i directly hook up the wire from and to the extra UPS battery the wires really get hot, i suspect that one battery is charging up the other and current is flowing through those wires like crazy.
Yeah that I would not recomend at all.

What you are doing is safe, if very slow.
 
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Just gonna throw this in...

I think some lead acid batteries (particularly non-sealed ones like car batteries) release hydrogen when charging. Could be a potential fire hazard if charging indoors?
 
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At 700mah? I doubt it.

There's a indicated build into the battery, supposed to lit green when it's charged. But it's all black meaning the battery is dead. If i turn on the UPS it refuses to even power ON when you pull the cord with no load lol. That voltage must be awefully low then.
 

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I am lucky that the battery of the car is in the trunk and not the hood, since the key only unlocks the trunk.
I'd be willing to bet there is a key hole hidden somewhere that unlocks the drivers door and would then let you open the hood. It might not even be near the door. The Corvette that I had put the key hole in the little overhang over the back license plate.

and let the alternator do the rest
This is extremely hard on the alternator. It is not recommended to charge a battery with an alternator, they are built to top off the battery a little and keep it charged, not charge a pretty well dead battery.
 
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So what do i do then? Keep the thing hooked to the UPS for at least 20 hours?

No there's no secret hatch or so. It's a cabrio with a locked roof that could only be opened from either inside (trunk) using a special tool or electronically when your inside the car. The key fits into the door but it wont do anything (i.e unlock). It only unlocks the trunk where the battery is sitting at.
 

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So what do i do then? Keep the thing hooked to the UPS for at least 20 hours?
I mean, at the rate it is charging now, to get 10Ah in it, you're looking at 14+ hours anyway.

I mean, you gotta do what you gotta do. And I'd be lying if I said I've never jumped my car with a dead battery and let the alternator charge the battery from dead. I'm just letting you, and anyone else reading, know it is bad for the alternator. So it might be time to invest in a proper battery charger.
 
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Since the wires got hot when i attached the UPS's internal battery, is'nt the same happening when the battery is getting charged slowly? Or is it a one way direction where current flows in and not out?
 
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That is a creative way to charge your car battery. I would have just grabbed a $10 float charger from Harbor Freight myself...
 

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Since the wires got hot when i attached the UPS's internal battery, is'nt the same happening when the battery is getting charged slowly? Or is it a one way direction where current flows in and not out?
The wires got hot because when you connect two batteries that are very different voltage, they try to equalize. So the UPS battery that was probably at 13v+ was just dumping current into the car battery that was likely a lot lower(probably below 10v). Because there was no current limiting device in the circuit, the UPS battery was transferring energy at the maximum current it could provide, which is going to get the wires pretty darn hot.

On the other hand, the UPS had a current limiter to charge the battery a lot slower so the wires don't get hot.

That is a creative way to charge your car battery. I would have just grabbed a $10 float charger from Harbor Freight myself...
The $10 float charger from Harbor Freight might actually charge the battery slower than the UPS. The UPS is probably charging at 700 mAh, the $10 charger from HF charges at 500 mAh.
 
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That is a creative way to charge your car battery. I would have just grabbed a $10 float charger from Harbor Freight myself...
Haha. It is the most easiest way of charging any battery in the first place. But it was "late" and everything here is as good as closed, knowing i might need the car tomorrow. A UPS is technically nothing more then a inverter / battery charger with a simple 7A battery put into it's housing. They are good for short power interrupts, depending on load it could run 220V for 5 up to 60 minutes.

But yes. It's not the brightest thing but it works!

On the other hand, the UPS had a current limiter to charge the battery a lot slower so the wires don't get hot.
So lets say, i leave the thing for 48 ~ 72 hours on the UPS, woud'nt the battery at some point have more current then the 7A battery? And will it even continue to charge untill the thing is full or at least holds its own capacity again? Or is it fairly simple, the wires wont be running into issues since the incoming current is nothing more then 0.7A?
 
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I mean, at the rate it is charging now, to get 10Ah in it, you're looking at 14+ hours anyway.

I mean, you gotta do what you gotta do. And I'd be lying if I said I've never jumped my car with a dead battery and let the alternator charge the battery from dead. I'm just letting you, and anyone else reading, know it is bad for the alternator. So it might be time to invest in a proper battery charger.
+1 to this.

It's not great for an alternator to charge one from flatout dead but it can be done.
A battery charger would be MUCH better to use if at all possible.
Man, I miss the days of having a generator in a vehicle - That WILL charge a battery from dead without issue and do it quickly too if the battery is good.

Anytime you have a wet cell battery, charging will generate this gas period. It's a nautral by-product of the charging process along with the battery getting warm/hot.

To clarify - A battery being warm while charging is normal and expected.
If it's to the point you really can't leave you hands on it to pick it up or just leave them on it period, then it's a hot battery.

Noted a post above about hitting a 12v battery with 24v's, that isn't too smart either because it generates excessive hydrogen gas and the battery itself will get HOT from the extra voltage, possibly causing the battery to ignite the gas and make it blow.

I do know since it gets hotter the electrolyte inside /evaporates/boils off and could leave you with a "Dry" battery.

Another thing is excessive amperage, not voltage used in charging - That too can boil off electrolyte and cook one good.
Accidentally did that to my bike battery this past spring using a 10 amp charge rate instead of the slower 2 amp rate - I forgot to change the charge rate when I hooked it up and cooked it but good in about 2-3 hours from being dead.

If you ever see a battery that's swollen it's probrably due to overcharging, those could also blow if trying to charge it and usually are low on electrolyte too.

Now.... If it's just slightly swollen it's probrably OK to top off the electrolyte level if possible and try a low amperage charge. If the battery gets really hot during the charging process it's resisting the charging and is bad - Replace it and make sure your alternator isn't overcharging the battery or you'll be replacing that one too before long. In any case if a battery gets really hot while charging it's probrably bad, would be best to replace it.

If a battery is already hot NEVER connect anything to it for charging/jumping off or disconnect anything from it either, best to simply leave it until it cools then deal with it.

In my time of working on equipment in the field such as forklifts, bobcats, skid-steer loaders and such these are things I learned just by having to work with such issues.
 
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In a very young era in my life, i used to work with electric scooters for older people. This is kind where i got my experience with battery's from. From small ones to big industrial ones, the tech behind it is pretty cool. Apart from that, i just wondered what would happen with the wires or UPS in the first place if the battery would be charged to it's full (75AH) extend. Its proberly not going to happen since the thing would be already at the right voltage on only 1/3rd of it's current charge. but enough to start the car, head for a longer distance and charge it while it drives.

I still have no clue on why it died completely. It was just a very low voltage (9V) which makes me think i either left the radio on or something else is pulling current from the battery while not in use. Or the battery is just near to dead, that's also a possibility since there's no DATE/YEAR markings on the battery itself. Battery's for cars usually go in between 3 to 5 years. Esp in colder days (which it is now) they start lacking power.

IMG_9704.jpg


A few hours later, there's sufficient voltage in now on which the UPS operates when i pull the mains. So it's charging. There's no heat coming off the UPS. It's a slightly warm transformer but nothing special. But for those curious on charging battery's, hell even with a PSU from a computer you could technically charge a battery up to whatever it supplies in amps on the 12V line. You need a small bridge to tweak up the voltage (13.8V instead of 12V) and its good to go.
 
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Has anyone here ever replaced their car battery with supercapacitor? If you have how well does it work?. I do believe you can buy them as a drop-in replacement.
 
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Capacitor loses their charge way faster then a car battery does.
 
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Car battery can sustain even up to 14.5V. Happens when you drive a car as well. The alternater is constantly switching in between various RPM's thus varying voltages. A charging controller inside the car or alternator makes sure the voltage is evened out for that matter. Some folks even charge their 12V battery with a 24V charger. It's possible, but just dont leave it on there too long.

I was just wondering if the 700mah (it takes longer, days even) was capable of Fully charging the 75AH thats marked on the battery. If i directly hook up the wire from and to the extra UPS battery the wires really get hot, i suspect that one battery is charging up the other and current is flowing through those wires like crazy.
Car batteries can sustain about to 15V on a fast bulk charge. Many alternators put out 14.7 or above. I also hate to brake it to you, but you are not likely starting your car with a 10AMP charge. Your battery likely holds between 75-90A of usable juice. You'll likely need to get 20 or more.

EDIT: 700ma is going to take forever to charge where you need it. Likely well into the next day.
 
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That is a creative way to charge your car battery. I would have just grabbed a $10 float charger from Harbor Freight myself...
The $10 float charger from Harbor Freight might actually charge the battery slower than the UPS. The UPS is probably charging at 700 mAh, the $10 charger from HF charges at 500 mAh.
Depending on state of charge in the battery at the start it might NOT even charge it at all and report you need a new battery. That is an issue now days with chargers that are sold these days. It relies on a computer chip to test the battery and if there is pretty much 0 volts showing it won't even try. Its nice to have an older charger laying around for those kinda days to least give a charge to the battery. I have that happen not long ago where someone left key in the "run" positon on my tractor and battery was 100% dead. Float charger wouldn't even try to charge it til i used non-computer one to give it a charge for 10-15min.

Car batteries can sustain about to 15V on a fast bulk charge. Many alternators put out 14.7 or above. I also hate to brake it to you, but you are not likely starting your car with a 10AMP charge. Your battery likely holds between 75-90A of usable juice. You'll likely need to get 20 or more.
EDIT: 700ma is going to take forever to charge where you need it. Likely well into the next day.
Depending on size of engine a car starter can draw if i remember right 100+amp's. Had battery test in a little sunfire with a 2.2liter engine and that is what their test detected when it started.
 
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The battery has 75AH for long term and 680A+ or so for CCA (Cold-crank-amps)

So even if it would have just 10A of current, the CCA would be around 100A which should be sufficient for a quick start. The thing does'nt take forever, it pretty much starts instant from my experience. If i would charge it for at least 24 hours it should be around 50 to 70% depending on this sheet:


Car battery capacityCar battery voltage (measured)Selected amperage car chargerCharge time of a car battery
75 AhAbove 12,40 V1A30 hour
I have'nt measured if it is or was 700mah, i just suspected that but it could be one amp as well on 12~13V. I do not have a multimeter around, if i could measure it i would know the definitive answer to that. But i suspect it's close to that number. Technically i could even hook it up to a PSU and start charging with that. My Antec 750W provides a 100A on 4 combined rails, it would last less then an hour or so to fully charge it at just 12V.
 
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