The hi amperage of those chargers aren't for charging batteries. It's to assist in starting an engine with low battery capacity due to discharge. It temporarily supplements an existing power system. AC powered jumper cable.

 

Mr. AI's post is pretty good. If you've dealt with car batteries, chargers, starters, for a long time, understand car batteries well, and really understand electricity, that's evident.

3-stage charging is what's happening these days, and there's plenty online to study up on that.

I think this thread isn't gonna gain much, it really doesn't need to, but Google may keep pushing people to it.

If you've gotten this far and still don't get it, go back! You probably don't understand something about voltage, current and resistance but it's all right there. Really.

 

The hi amperage of those chargers aren't for charging batteries. It's to assist in starting an engine with low battery capacity due to discharge. It temporarily supplements an existing power system. AC powered jumper cable.

An example of how they are being sold and used:

Autozone will use one of these fancy 3-stage 50+ amp chargers they also sell to fast charge your battery in just 30 minutes. That's not for a jump, though these charger units also support brief output of 400 amps, etc. so they can jump-start a car.

I'm skeptical that charge is any good for the battery, based on what I know and what people are saying here. However, if this equipment and services is actually destructive to a car battery, how do the stores and manufacturers get away with selling these things as professional-grade chargers?

How long would you say a 100-amp charge current into an automotive battery is safe to apply without damaging the battery?

 

I am confused. First you come in and pose a question on an old thread for reasons unknown, and then you are a self proclaimed expert on battery chargers. What gives?

....

I'm not an expert, self-proclaimed or otherwise. Some of you guys are!

I have some understanding and experience with lead-acid charging, and based on that and what I've read above, I was replying with my current understanding and knowledge, together with additional questions. I'm admittedly confused and nervous about why these high amp chargers exist, whether they're being misused by professionals, and if there's any safe way to use them at all!

 

Mr. AI's post is pretty good. If you've dealt with car batteries, chargers, starters, for a long time, understand car batteries well, and really understand electricity, that's evident.

I liked Mr. AI's post quite a bit myself too!

However, what bothered me about it is was his comment that the charge voltage would have to go way above 14V to support a current through the battery like 60-amps. These chargers ain't gonna go that high! Since battery won't actually receive 60-amps, especially not under 3-stage charging with current limiting, that's why I'm still confused whether there is a safe way to use that charger.

 

Here is how I would answer your question. As an alternator and starter rebuilder, I witnessed first hand the effects of a sulphated battery and what it can do to a perfectly good alternator in a short period of time. One case I had was on a Ford Tempo that was at a dealership. Long story short, within 10 minutes of installing my newly rebuilt alternator, they burnt the thing out completely and wanted warranty. I rebuilt the alternator and brought it there myself and put it on and then watched the amperage on startup. It went straight to 90 amps and within 2 minutes, I could have fried up some bacon and eggs because it was so hot. The voltage never moved over 14.6 VDC.
After replacing a severely sulphated and overaged battery, I tried it again. The unit now ran at 20 amps and cool as a cucumber.
So now about the chargers. If the charger is capable of putting out high voltage (pressure) and it is set to a high amperage setting, it will do whatever it has to to force those electrons in to the battery no matter how much sulphation (resistance) there is. The end result will be gassing and possibly a catastrophe. Chargers are being misused by technician and back-yarders alike because they don't understand how to properly charge a battery. I have monitored voltage output on many chargers while my students are watching, and show them that it will easily climb over 15.5 VDC and enter the territory where gassing starts to occur if it is not supervised. By setting it at a lower rate, no problems are found and everything is safe.
These chargers are made all over the world, some better than others and some a lot safer than others. Everything in this world now is buyer beware. There is good and bad, you do the homework.

 

No settings on my 100-amp charger, I have personally witnessed the bulk stage max voltage is 13.7V and whatever the current is when it gets to that point, that's the most it'll be. It is not a made to push it's max current into a battery, which is not how 3-stage charging works.

So, lets say the current is 80 amps at that max 13.7V, this would be okay for the battery? Or should the time at this current and the battery temperature still be closely monitored?

Very interesting story about the alternator and sulphates battery! I'm going to check that with my DC clamp meter periodically!

 

So, lets say the current is 80 amps at that max 13.7V, this would be okay for the battery? Or should the time at this current and the battery temperature still be closely monitored?

It depends, just like people at a buffet. Some people can wolf down a side of beef without blinking while others can't finish a plate of fried chicken. A proper type battery with large reaction surfaces might easily handle 80 amps at that voltage. Even if the spec's say it should you need to closely monitor the battery as you can't believe what you read about batteries from some manufacturers.
http://www.trojanbattery.com/pdf/The Real Facts on U.S. Battery.pdf

 

so I'm wondering how is that considered safe for a battery? Most people seem to recommend 10-amps max. for charging car starter batteries.

Common misconception. Most vehicles today have small <50Ah batteries yet have 100+ amp alternators.

As long as the voltage is kept under ~14.5 - 15 volts you pretty much let a battery take all the current it wants. Most wont draw high current for more than a few tens of seconds before the surface charge on the plates inside the battery starts to lower the current draw.

I've built many high current battery chargers over the years and I have never had an issue with overcurrent being the chargers had basic output voltage limits that stayed under ~15 volts.

 

I would say it totally depends on the state of charge of the battery as others have said above.. Not so much the potential charging current. I do not think putting that kind of current on a discharged battery or even one at less than 90% charge state is a good idea. On a fully charged battery? fine.

If for example you were to run your car battery down to 50% charge every day, then charge it at 70 Amps, I can tell you that battery will have a short life. The high amp output of modern alternators is safe for FULLY CHARGED batteries...but not so much for discharged batteries. In fact a deeply discharged car battery can draw so many amps off of an alternator as to damage the alternator.

In my experience (limited as it may be), during charge the higher the amps, the hotter the battery. That's simply because you're moving a LOT more electrons through the same sized pipeline (the surface area of the plates and the internal metal conduits). And heat is not good for a battery.
Higher amps just means that potentially more current CAN flow into the battery (if there is room for more electrons to flow between the plates)......but that doesn't mean it's GOOD for the battery.

Higher amps during charging equates to higher plate temperatures and that can result in plate warping and other damage....again, when charging the battery...Versus maintaining it at full charge when there is much less electron flow.

True, a fully charged battery will not draw more current than it can considering there are fewer places for electrons to move to, but providing that high current to a battery that is low on charge could cause damage.

I always recommend a limited charge rate of about 8 amps MAX for a deeply discharged battery. 2 amps (if you have the time) is even batter.

If I'm talking trash feel free to put me in my place

 

An example of how they are being sold and used:

Autozone will use one of these fancy 3-stage 50+ amp chargers they also sell to fast charge your battery in just 30 minutes. That's not for a jump, though these charger units also support brief output of 400 amps, etc. so they can jump-start a car.

I'm skeptical that charge is any good for the battery, based on what I know and what people are saying here. However, if this equipment and services is actually destructive to a car battery, how do the stores and manufacturers get away with selling these things as professional-grade chargers?

How long would you say a 100-amp charge current into an automotive battery is safe to apply without damaging the battery?

I liked Mr. AI's post quite a bit myself too!

However, what bothered me about it is was his comment that the charge voltage would have to go way above 14V to support a current through the battery like 60-amps. These chargers ain't gonna go that high! Since battery won't actually receive 60-amps, especially not under 3-stage charging with current limiting, that's why I'm still confused whether there is a safe way to use that charger.

Hello there,

The power heating temperature is based on the amount of power that heats the battery vs the surface area of the battery that is exposed to some sort of cooling such as free air. As the battery is charged it heats up, and the surface area and ambient temperature and charge current and charge acceptance and type of chemistry determine the temperature while charging. For some batteries like NiMH, they can actually cool while charging until they are fully charged and then they start to heat up. For lead acid i think they always heat up at least a little.

For higher current it makes sense that they would heat up more, so there has to be some limit. For a transient charge the other parameter that enters into the picture is the specific heat capacity of the battery which would include the plates and the acid and the plastic. For a given charge current the temperature will rise at a certain rate due to the specific heat capacity of the construction and that governs the max temperature at the end of some time like ohe hour for example. It should be obvious that if you supply 10000 amperes it will heat up much faster than if you supply just 10 amps. The degree of temperature rise could cause problems if it heats up to a temperature that is too high, and also the charge acceptance may go down with higher temperatures.

So there is a lot to consider when charging at high current. There is also the problem of a spark if one of the leads becomes disconnected.

As to the charge voltage though, it has to be high enough to push the required current through the battery, and this depends a lot on the internal resistance of the battery. For one battery i have, when it is not charged correctly for a while the internal resistance goes up and thus it makes ti harder and harder for a constant voltage charger to charge the battery. Once i charge it with a slightly higher voltage though, the internal resistance comes down and then it charges ok with a lower voltage for a while, until the resistance goes back up again. I went through this for many months with an old Hyundai i had for many years. The alternator voltage was not quite high enough to charge the battery correctly.
During the charge with the power supply, i would have to set the voltage to a higher value like 14.2 or 14.4 volts or maybe even higher. That was to get the higher current flow .like 5 amps ro so. Once the internal resistance came down though, it would charge at 14v or maybe even 13.9 volts.
This also tells me how critical the voltage level can be.
I still have the battery but i got rid of the car due to some other problems, but i still keep it charged up.

Batteries are just not as simple as we would like to believe they are sometimes
One thing is for sure too and that is that batteries are not all the same, even of the same chemistries.

 

I would say it totally depends on the state of charge of the battery as others have said above.. Not so much the potential charging current. I do not think putting that kind of current on a discharged battery or even one at less than 90% charge state is a good idea. On a fully charged battery? fine.

A fully charged battery should only take a float charge trickle current, so no way a high current is a good idea, unless you're trying to overcharge it.

The takeaway I'm getting out of this discussion with so many varying viewpoints and opinions is a high charge current on a automotive starter battery with thin plates is not generally a good idea, a slow charge is preferable because the internal structure is delicate. If done, it should be closely monitored and not allowed for very long if the battery doesn't lower the charge acceptance itself.

High current chargers are probably intended to be used more on deep cycle lead acid batteries than starter ones. That's why I bought my 100-amp charger, and it works well with those, but I probably should get a much lower amp charger to use on a car battery.

 

Something else is that a battery that has been just discharged quickly benefits from a quick charge. For example, if something like 14.2v @ unlimited current were available and hooked up to a battery that was just prior quickly discharged, if it took charge at 100 amps that likely would be better for the battery than a 2 amp slow charge. That is because a battery being in a discharged state is damaged more the longer it is in that state. Probably why it accepts faster charge is that the chemical reaction is more easily reversed before there has been much internal fluid circulation.

 

The rule of thumb I have always used is that a battery can take whatever recharge current that it can give as a discharge current so long as the peak charging voltage is not exceeded.

There have been many times where I have used a high powered constant voltage source (MIG/Wire) welder power supplies to recharge 12 or 24 volt battery systems in situations where there was no other source of power. Never once had a problem with it so long as the charging voltage was kept around 15 volts for the 12 volts system and 30 volts for the 24 volt systems.

In fact many commercial welder generator rigs come with dedicated charger/booster modes built into them just for that purpose.

Then there's the reality of what sort of service life you can gains from ideal charinge conditions Vs real world ones. The reality is in almost all normal situations there is so little added service life to gain that using ideal charging methods they are not worth the wasted time they involved for day to day use starting/mobile deep cycle batteries. Over discharge does far more harm and life reduction to a battery than does Ideal VS good enough recharge gains.

For the work I do I could care less if a battery lasts for 5 years Vs six. They are are consumable that eventually wears out and the work I need to do is worth way more than any battery ever will be. If I left the lights or some other thing on and ran a battery down overnight and need to get going for work I am certainly not going to waste a full day waiting a for a tiny idea charger to do its job.
I'm going to grab the highest powered charger I have and get going as fast as possible and then let the vehicles or machines charging system take over from there until it's happy with things even if it means I have to use my welder generator to hit a dead 12 volt battery with 15 - 16 volts and 300+ amps for 2 - 3 minutes to do it.

 

The rule of thumb I have always used is that a battery can take whatever recharge current that it can give as a discharge current so long as the peak charging voltage is not exceeded.

Hi there,

I can tell you with absolute certainty that not all batteries are like that. It depends on the battery if it will take it and exactly how long it will take that kind of charge.

Case in point, i have Li-ion batteries that i purchased some time ago to use in a high power LED light. I had to get these because the other ones i had were not rated for a high enough discharge current that the new light needed to run it at full power.
The cells are high quality and each rated for 30 amp discharge. The manufacturer quotes a max charge current of 4 amps however. Since they are around 2 ampere hour cells that means they can be charged in roughly about 1/2 hour, which is 30 minutes and is not bad at all. Interestingly, the portable drills that run on these cells recharge in about 30 minutes too.
Now if we charged at 30 amperes, i think the cell would have a problem. If we charged at 20 amperes i think that would be a problem too. At 20 amperes we'd be able to charge in roughly 6 minutes, wouldnt that be nice?
But if we ruin the cells or worse then we cant use them at all

Lead acid cells are bigger so they can take a large over current for a while, but there is a time limit based on their physical size and average specific heat capacity. If we do this for too long the battery is going to over heat. Now some overheating is allowed, but if it gets too hot it's going to cause big problems.
The deciding factor then is temperature over time.

There's always a recommended maximum charge current though in the data sheet if you buy a battery that has a data sheet. I can remember seeing max charge current ratings that are always less than the discharge rating in the data sheet.

 

I can tell you with absolute certainty that not all batteries are like that. It depends on the battery if it will take it and exactly how long it will take that kind of charge.

Yes. Different topologies have different characteristics. I took it the OP was talking about larger lead acid based types to which I have never been able to over current one on a recharge on purpose without putting a excessive voltage to one. Self taper off effects always kept the current within limits even when near maximum discharge.

 

Yes. Different topologies have different characteristics. I took it the OP was talking about larger lead acid based types to which I have never been able to over current one on a recharge on purpose without putting a excessive voltage to one. Self taper off effects always kept the current within limits even when near maximum discharge.

Hi,

Oh yes ok. I would think it would take longer to see a large battery heat up.

I mostly work with the smaller ones like 7 to 15 ampere hour sealed LA, except for a couple car batteries. My 7 (or 8) ampere hour batteries have a max charge current of about 2 amps, as recommended on the data sheet. The max discharge current is pretty high though.

Now that i think about it, that may be because the discharge current time is always limited because there is a limited amount of stored charge in the battery and therefore it can not overheat on discharge. During charge however it may be possible to charge it for hours and hours.
I also noticed that they specify a max charge voltage too, per cell, and at certain temperatures and with a slope with temperature. That may be worth noting.

For car batteries though i dont remember finding any actual ampere hour ratings, they usually just give cold cranking amps. The battery sizes are significantly different though. The battery in my car now is almost twice the size of the battery in my older car. That tells me that the ampere hour capacity is a lot higher for the bigger one. Dont have any actual numbers for either one though.

 

Now that i think about it, that may be because the discharge current time is always limited because there is a limited amount of stored charge in the battery and therefore it can not overheat on discharge. During charge however it may be possible to charge it for hours and hours.

On a good 12 volt LA battery I have never found it possible to overcharge one with a constant voltage power source that operates under 15 volts regardless of how many amps, 10's of amps or even hundreds of amps it was capable of.

 

On a good 12 volt LA battery I have never found it possible to overcharge one with a constant voltage power source that operates under 15 volts regardless of how many amps, 10's of amps or even hundreds of amps it was capable of.

Hi again,

Yes but one of my points was that time was involved and by stating it as a static problem you make it sound like you can never overcharge it but i believe you dont really mean that.

For example, by saying "hundreds of amps" it sounds like you can charge it until the cows come home at 100 amps and nothing will happen, but what you really have to include is the time it charges at say 100 amps and how it tapers off as the voltage rises. 100 amps at 15v volts is 1500 watts as i am sure you know, and that is more power than your typical room space heater but confined to a relatively small package. Yes it wont heat up right away, but over some time it will. The question then is just how long will it take that. It cant be too long and that would be typical for a quick charge, but then it tapers down to a relatively low current.

 

Yes but one of my points was that time was involved and by stating it as a static problem you make it sound like you can never overcharge it but i believe you dont really mean that.

I don't really feel like playing the read-between-the-lines sentence structure semantics game given I clearly pointed out ahead of the amperage value references you are using, as an apparent carte blanche all inclusive justification, to throw whatever amperage anyone wishes at a battery as if input voltage required to do it would be irrelevant to the changing process, which it's not.

I have never found it possible to overcharge one with a constant voltage power source that operates under 15 volts regardless of how many amps

I guarantee that when using a constant voltage power source of 15 volts or a bit less for charging a common 12 volt starting or deep cycle battery that is in good working condition but heavily discharged it will reach its charged up point before it gets too hot to do damage. Initial current for the first few to tens of second may be way higher than the recommended continuous charge rating but it won't happen long enough to cook a normal battery.

.