recharging battery

[jimbob35]

My batteries a bit low due to little use over the last few months, i was wondering if i can hook it straight up to my car battery (engine off!) to boost its charge?

cheers

[GregS]

Engine off on the car would discharge the car battery until the 2 batteries balanced out, assuming the bike battery doesn't have a bad cell. With the car running, at idle, it would charge the bike battery and the regulator in the car would prevent over charging, assuming your car has a properly working charging system.

[jimbob35]

i heared somewhere that running the car would produce too much power and overload the bike batt?

i dont mind the car discharging a bit as i do so many miles on it.

[ATOMonkey]

That's simply not true. Voltage is voltage and amps are amps. The only way to "overload" a battery is to charge it at a higher voltage than it was designed.

Voltage is similar to pressure and amperage is similar to flow. If you have 12 psi in a jar, and try to blow 12 psi of air into the jar, will the jar explode? No, because the pressures are equal, you have no flow.

If you have a bad battery, it will attempt to eat itself and can produce enough hydrogen for a small fire.

[Black_peter]

That's simply not true. Voltage is voltage and amps are amps. The only way to "overload" a battery is to charge it at a higher voltage than it was designed.

Not exactly..

Think of it this way, (to use your "air" analogy)
Two balloons
One that is made of very flexible rubber.
One of stiffer rubber.
Both can hold 1000 liters of air.
If you fill them both at 1 liter/ minute everything is cool.
If you fill them both at 100 liters/ minute the stiffer one might burst because the rubber cannot stretch fast enough for the incoming air.. Notice I didn't mention the pressure. Because Voltage is to pressure as Amperage is to flow. Pressure doesn't matter.

The rate at which you charge a battery is not the rate it "wants" the voltage but the rate the charger is limiting the voltage. The battery might be happy to take 10 amp charge but melt, boil or explode in the process. Just like the balloon. It doesn't know any better.. A different battery might be happy charging at 100 amp.. Due to it's size, a motorcycle battery should be charged as low as possible. 2 amp is safe. Less is better. A car charging system is designed for the battery installed in the car. Not just any 12 volt battery.

[ATOMonkey]

So, you're saying that the internal resistance in a 12V lead acid battery varies based on the size of the battery?

Also, an alternator is regulated, either internally or externally through field modulation to not exceed 14 volts. Amperage however, if dependant on the size and speed of the alternator as to what it's physically capable of producing. Most alternators max out at 40-60 amps.

I'll have to check my battery charger, but I believe it is regulated to 12-14V as well. The 10A vs 2A setting is still 12-14V.

Amperage is simply the product of voltage and resistance. It's not something you can force.

[jimbob35]

Part of my problem was there was absolutely no liquid in the battery! heh

The battery is probably on its way out, but for the time being ive filled it with electrolyte and hooked it up to my car for an hour.. seems to be starting my bike just fine now

[GregS]

Good deal. Just look at the backlash you started with that original question. Now just say something about putting large tires on, or using pod filters, or regular car oil.

[loudnlow7484]

I'm sorry, but I have to respectfully disagree with the whole "only charge bike batteries under 2 amps" thing. Now, batteries are something of a black art to me, so I'm not going to pretend to know in depth how they function. All I can really give is speculation, based on my other, rather extensive, electrical experience.

Ex #1- In car audio, we would routinely install 300-400 amp alternators to keep up with the current demand from a big sound system. If your logic were correct, we would destroy the vehicle's battery the first time it died, and was jump started. This just didn't happen.

We also had some issue with different types of batteries. For example, when charging an Optima battery from totally dead, it would take ssssooooooo long to charge. Even charging at 14 volts, they were only taking something like 2-4 amps in. We refer to this as "Optima's-are-pieces-of-s**t Syndrome".

Of course, the most obvious example is in your bike itself. If your battery dies, and you jump start your bike, the alternator in the bike will put out more than 2 amps, so why would you feel the need to charge it that slowly, when the bike itself will charge it at 10x that rate?

[Black_peter]

So, you're saying that the internal resistance in a 12V lead acid battery varies based on the size of the battery?

No. I'm not saying anything about internal resistance.
Remember that a battery is not like a light bulb or a relay. It is a bridge between electrical and chemical. It is far more complex then just E=i/r..

I'll have to check my battery charger, but I believe it is regulated to 12-14V as well. The 10A vs 2A setting is still 12-14V.

Why are you fixating on voltage?

I'm sorry, but I have to respectfully disagree with the whole "only charge bike batteries under 2 amps" thing.

I never said that.

Now, batteries are something of a black art to me, so I'm not going to pretend to know in depth how they function.

then your disagreements and arguments from this point on hold no weight do they? Charge your battery however you like, I'm not pretending to be laying down any laws here..
However the battery industry does, they give the formula of c/5 where "c" is the Ah of the battery. The Kat has about a 8 Ah battery so you should charge it at 1.6 amp.

[ATOMonkey]

Charge Factor — A number representing the time in hours during which a battery can be charged at a constant current without damage to the battery. Usually expressed in relation to the total battery capacity, i.e., C/5 indicates a charge factor of 5 hours. Related to charge rate.
Charge Rate — The current applied to a cell or battery to restore its available capacity. This rate is commonly normalized by a charge control device with respect to the rated capacity of the cell or battery.
Battery charging takes place in 3 basic stages: Bulk, Absorption, and Float.

Bulk Charge - The first stage of 3-stage battery charging. Current is sent to batteries at the maximum safe rate until voltage rises to near (80-90%) full charge level. Voltages at this stage typically range from 10.5 volts to 15 volts. There is no "correct" voltage for bulk charging, but there are limits on the maximum current that the battery and/or wiring can take.

Absorption Charge: The second stage of 3-stage battery charging. Voltage remains constant and current gradually tapers off as internal resistance increases during charging. It is during this stage that the charger puts out maximum voltage. Voltages at this stage are typically around 14.2 to 15.5 volts.

Float Charge: The third stage of 3-stage battery charging. After batteries reach full charge, charging voltage is reduced to a lower level (typically 12.8 to 13.2) to reduce gassing and prolong battery life. This is often referred to as a maintenance or trickle charge, since it's main purpose is to keep an already charged battery from discharging. PWM, or "pulse width modulation" accomplishes the same thing. In PWM, the controller or charger senses tiny voltage drops in the battery and sends very short charging cycles (pulses) to the battery. This may occur several hundred times per minute. It is called "pulse width" because the width of the pulses may vary from a few microseconds to several seconds. Note that for long term float service, such as backup power systems that are seldom discharged, the float voltage should be around 13.02 to 13.20 volts.

A normalized rate over a 5 hours span of 1.6 amps is what is a small battery that you would use in a motorcycle is rated at. This rate is based on the chemistry and size of the battery. When using a 12-14 volt source to charge, it will ALWAYS charge at this rate. It will charge very fast at first, then taper off quickly to give an overall charge rate of 1.6 amps.

Chemically, you have a much much greater capacity to charge when PbSO4 has been plated onto the spongy lead matrix. This sets the voltage potential betwen the battery and the source. A smaller battery will absorb a lower amperage over the same time period as a larger battery, but initially both batteries will absorb charge at the same amperage based on the internal resistance of the battery.

As the battery charges, the PbSO4 on the lead will diassociate itself and move back into solution creating PbO2 + SO4 (aq) + H+ + e-. This creates a charge, and LOWERS the charge difference between the source and the battery. ie, if the battery has a 8 Volt capacity and your source has a 12V capacity, you have a 4V potential driving the flow of electrons. Now you use your V = IR and determine that for a constant resistance with a decreasing voltage difference, you have a decrease in current as well.

This is why most batteries will charge in a logarithmic manner, giving a RMS average of 1.6 amps over a 5 hour period when the actual c/s varies over time and is dependant on potential difference.

Therefore, as long as you ONLY use a 12V source, you can charge a battery with a freakin' nuclear reactor and it'll charge the same way every time.

The only difference is that you can be amperage limited by the power rating of your source. Since P = VI, for a constant voltage and constant power, you will have a constant amperage as long as the battery can absorb the charge at that rate.

[ATOMonkey]

Now, the problem occurs when you exceed the ability of the cathode to properly absorb the PBSO4, at which time, you start to electrolyze the water producing hydrogen and oxygen that eventually explodes as the pressure increases.

This normally happens to old batteries where the spongy lead matrix is no longer very spongy and the electrolyte level has also decraesed from use. However, it can also happen to healthy batteries when you exceed 14 volts for an extended period of time, such as on a "quick charge" setting on your battery charger. Quick charge is closer to 18 or 19 volts generally.

That is why all non-maintenence free batteries have vents, and must be measured for specific gravity and refilled periodically.

[The CyberPoet]

I'm sorry, but I have to respectfully disagree with the whole "only charge bike batteries under 2 amps" thing. Now, batteries are something of a black art to me, so I'm not going to pretend to know in depth how they function. All I can really give is speculation, based on my other, rather extensive, electrical experience.

The reason for the 1-amp rule (or whatever the battery manufacturer says is the max sustained charging rate, which is 0.9 amps for the 98+ Kat OEM maint free batteries according to Yuasa), given a steady charging voltage in, is simple as pie: heat. The more chemical conversion goes on, the more heat is generated, and batteries' ability to store/shed that heat can hit a critical threshold that the case can't sustain (ditto gas pressure, as mentioned by ATO).

It's not too horrible a thing to charge at 4 or 8 amps -- in short cycles, like 10-15 minutes at a pop -- but the battery needs to cool-down before it goes back to that charge rate again -- which typically means you'll effectively be back at a lower charging rate again once you average it all out. Obviously, the cool-down vs. high-charge-rate time requirements varies with environmental factors (easier to shed heat in a Wisconsin November evening than a Florida June afternoon), but it's still the same concept (and reabsorption time for the gas doesn't vary all that highly).

We also had some issue with different types of batteries. For example, when charging an Optima battery from totally dead, it would take ssssooooooo long to charge. Even charging at 14 volts, they were only taking something like 2-4 amps in. We refer to this as "Optima's-are-pieces-of-s**t Syndrome".

Optima's claim to fame is the concept that spiral-winding plates (instead of stacking them next to each other) permits more surface area for a higher CCA (cold crank amperage) and means plates that shed, shed onto the next plate down.
After evaluating their materials a year or three ago, I came to the conclusion, at least in terms of their motorcycle batteries, that they were blowing smoke and using false numbers (numbers disclaimed elsewhere in their same documentation as being expressed in non-standard terms that would almost double the CCA rating of any battery by any manufacturer).

Cheers,
=-= The CyberPoet

[loudnlow7484]

The reason for the 1-amp rule (or whatever the battery manufacturer says is the max sustained charging rate, which is 0.9 amps for the 98+ Kat OEM maint free batteries according to Yuasa), given a steady charging voltage in, is simple as pie: heat. The more chemical conversion goes on, the more heat is generated, and batteries' ability to store/shed that heat can hit a critical threshold that the case can't sustain (ditto gas pressure, as mentioned by ATO).

It's not too horrible a thing to charge at 4 or 8 amps -- in short cycles, like 10-15 minutes at a pop -- but the battery needs to cool-down before it goes back to that charge rate again -- which typically means you'll effectively be back at a lower charging rate again once you average it all out. Obviously, the cool-down vs. high-charge-rate time requirements varies with environmental factors (easier to shed heat in a Wisconsin November evening than a Florida June afternoon), but it's still the same concept (and reabsorption time for the gas doesn't vary all that highly).



Optima's claim to fame is the concept that spiral-winding plates (instead of stacking them next to each other) permits more surface area for a higher CCA (cold crank amperage) and means plates that shed, shed onto the next plate down.
After evaluating their materials a year or three ago, I came to the conclusion, at least in terms of their motorcycle batteries, that they were blowing smoke and using false numbers (numbers disclaimed elsewhere in their same documentation as being expressed in non-standard terms that would almost double the CCA rating of any battery by any manufacturer).

Cheers,
=-= The CyberPoet

Thank you for that explanation. The heat part, I can understand absolutely. What I didn't see was a reason why you would be required to charge a battery so slowly, when I can't see any electrical reason to. Heat is a different consideration........

I never had anything but problems with the Optimas..... charged slow, some wouldn't hold a charge at all, average lifespan of about 1 year..... just never were very good. We used a series of batteries called "kinetic", I think, that we had a lot of luck with. I'm pretty sure they were just lead-acid batteries, though. Nothing special, but they were solid, and put out the current we needed them to.