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GlenT
05-07-2010, 03:45 PM
I just bought a new battery charger. It is one of those digital charges that has multiple charging rates and computerized battery assessment features. It has a low charge rate of 4 amps.

Now, I am aware that the conventional wisdom is that you should not charge a motorcycle battery (or any battery) at a rate that is greater than 1/10th the AH rating. In the case of the ST1300 stock battery, that's 1.2 amps.

Now, I know that the digital charger will assess the current state of the battery and the charging rate will be adjusted accordingly. The 4 amp charge rate is only a hard limit, not what it will actually charge the battery at.

I have been using an older charger that has a variable rate and a 2 amp rate mode, that has worked fine in the past. But it has gone 'missing' from my garage.

So, my question is, what does the voltage regulator on the ST1300's alternator actually limit the charge rate to at the battery? The alternator can put out a max of something like 60 amps. I'm guessing that it would not do that at the battery. But I find it hard to believe that it is also limited to 1.5 amps maximum when the bike is running at highways speeds and you've run the battery down trying to get the bike to start.

FOG
05-07-2010, 04:08 PM
No it is not limited to 1.5 amps, as the fuel pumps, ignition lights and farkles are drawing off current, so in loose theory, those electrons get detoured before they go into the battery.

Heat from fast/over charging is what kills the battery, it can warp plates and boil the electrolyte out of the battery putting it to an early death. 4 amps is a little hefty for prolonged charging, and if left at that level for long periods would soon boil it dry.

GlenT
05-07-2010, 04:30 PM
Let's say the battery had been discharged down to about 70%. There was enough juice to get the bike started. So you head out to the open highway and you're motoring along at 60 mph. How many amps is the battery currently drawing from the ST1300's charger?

The digital charger starts off at a low amp rate and then increases it while monitoring the battery state until it finds a level that the battery will take (within the limit that you have set, such as 4 amps). When the battery approaches 75% charge, the charger begins to back off the amps until the battery reaches 100% charge. It then goes into maintenance mode.

Blrfl
05-07-2010, 05:39 PM
Let's say the battery had been discharged down to about 70%. There was enough juice to get the bike started. So you head out to the open highway and you're motoring along at 60 mph. How many amps is the battery currently drawing from the ST1300's charger?

That depends almost entirely on the state of the battery and what loads are present at any given instant.

The voltage regulator acts as a switch for the alternator's field coils that turns them (and therefore the alternator's ability to produce electricity) on when the voltage falls below some threshold and off above some other threshold. 13.5-14.5 volts is a pretty typical range.

When the battery is weaker, its resistance is lower and current will flow into it and charge it. As its voltage increases, so does its resistance, which means the amount of charging current decreases. At some point it will reach the regulator's upper threshold and the alternator is shut off. The load on bike will then start draining the battery and the cycle will eventually repeat. If there's sufficient load (from lights, farkles, etc.), it will drag the entire system's voltage into a range where the field coils stay on all the time, which is where the extra alternator capacity helps power everything.


--Mark

FOG
05-08-2010, 06:26 AM
Let's say the battery had been discharged down to about 70%. There was enough juice to get the bike started. So you head out to the open highway and you're motoring along at 60 mph. How many amps is the battery currently drawing from the ST1300's charger?

My bet is you might see as high as 10 amps, but it would quickly taper back, as the voltage rises, and before heat built up.


The digital charger starts off at a low amp rate and then increases it while monitoring the battery state until it finds a level that the battery will take (within the limit that you have set, such as 4 amps). When the battery approaches 75% charge, the charger begins to back off the amps until the battery reaches 100% charge. It then goes into maintenance mode.

Sounds like the low rate is MUCH less than 4 amps. again if you do not have a DC amp meter (many cheap VOM's do have a 10 amp shunt) you can do the poor mans amperage monitor. Place one of those "ice pick" 12 volt testers in series with one of the leads, it should gradually go from bright on a low battery to barely glowing, or even not glowing as the battery reaches full charge.

GlenT
05-08-2010, 11:24 AM
Thanks guys. I believe that this does answer my question. I think that much of the conventional wisdom about charging batteries is based on older charger technology. I was interested in the the fact that much that is written about charging motorcycle batteries is based on the idea that the amperage should never exceed 1.2 amps. But I just couldn't see how that would be the case when the battery is charged by the bike's alternator.

My new charger also has the ability to display output voltage or amperage while it is charging. It's also (supposedly) has a cycle for desulphating a dead battery. I have an old battery I pulled out of my wife's beemer, so I will test the new charger on that and see what happens. I'll monitor the battery's temperature with my spot thermo while I'm doing it.

GlenT
05-08-2010, 07:14 PM
Well, the new charger did a good job of recharging a flat (less than 50%) 5 year old battery from an r1100r. I set it to 4 amps (max). It started off at 2.2 and gradually increased to 4 amps. When it hit 90% it gradually decreased the output until the battery was fully charged, in about 6 hours.

My spot temp. meter says that the battery never got above 91F. By the way, this battery has printed on it that it should not be charged above 6 amps, the output voltages also stayed withing range for this battery.

Silver Bullet
05-08-2010, 07:28 PM
Sounds like that charger will do the job,and as you said todays tech with the electronic monitoring is the way to go !

:slv13: MIKE

Avtrician
05-08-2010, 07:34 PM
The Regulator for a Bike, Car, Aeroplane regulates the Voltage from the generator/alternator. for bikes/cars its 13.8 V (max 14.2) If your battery is flat, it will take as many amps as the Charging system can deliver until the voltage rises. As the Voltage of the battery approaches 13.8V the current (Amps) drops. It doesnt take long to recharge the battery.

A current regulated system will deliver the set current for ever. Unless connected to a timer circuit, this can cause overcharging. A constant current charger should be set to charge at the C10 rate for 150% of the battery rating. IE a 40 Ampere Hour battery should be charged at 4 Amps for 15 Hrs. Car and bike systems are Constant Voltage, so overcharging can not happen (unless the regulator goes tits up) {Tits Up = Oz for buggered {Broken}}

Brock

Aero Eleco and more.....:D:D

mikew1231
05-08-2010, 08:19 PM
I'll have to add my two cents, if we take a quick look at Ohm's law (Resistance=Voltage divided by amps), if the resistance stays the same (I think it will) and the voltage increases the current will drop.
I believe the regulator used in vehicles is called a voltage regulator. I'd use a zener diode to perform the work, but I really don't know how voltage regulators work, and don't confuse a zener diode with the diodes in a bridge rectifier...

Please see the voltage regulator discussion on Wiki [ame="http://en.wikipedia.org/wiki/Voltage_regulator"]Voltage regulator - Wikipedia, the free encyclopedia@@AMEPARAM@@/wiki/File:Question_book-new.svg" class="image"><img alt="Question book-new.svg" src="http://upload.wikimedia.org/wikipedia/en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png"@@AMEPARAM@@en/thumb/9/99/Question_book-new.svg/50px-Question_book-new.svg.png

To answer the original question, I'll throw an amp clamp on my bike the next time I get a chance and I'll let you know how many amps the alternator typically puts out in different situations, but my gut tells me if won't be over an amp or two most of the time and actually less than an amp at idle after about a minute from a cold start.

Avtrician
05-08-2010, 10:49 PM
I think you will find that the alternator will most likely be delivering around 10 Amps, seeing as there are headlights on, fuel pump running and ignition. The current going into the battery will be low. There should not be a high current coming out (discharge) from the battery, this would indicate an alternator problem.

For those with Ex Cop bikes, the Voltmeter (if fitted) should indicate 14 Volts.

GlenT
05-09-2010, 11:09 AM
I'm guessing that the voltage regulator on the bike regulates the voltage to meet the current (amp) demand of the battery. So if the battery is low, voltage will be higher to meet the demand. That's what this charger does. I can monitor the voltage output or the amp output while it is running (digital display).

The charger has some kind of logic built in that starts the battery off at a lower voltage, then raises it while monitoring how the battery is accepting the charge. If the battery fails to accept a charge, then the charger can switch to a de-sulphating program, which it will repeat about 4 times, before declaring that the battery is not chargable.

The old beemer battery was useful in that it had limits printed right on the side of it for charging: 14.40 to 15.0 volts, 6.0 amps (max initial charge). This is a 20 AH battery. I monitored the charger output, which held within this range when it was set to 4 amps (max) output.

From what I've read, the danger is in overheating a smaller battery. The battery temp. should not go beyond 107 F. I monitored mine with a spot temp. meter and it reached the low 90's when it was about 90% charged.

I am going to try charging the my old ST13 battery next (once the new one is installed) and see what it does. It is smaller (about 12AH) compared to this beemer battery.

okmurdog
05-09-2010, 12:44 PM
I'm guessing that the voltage regulator on the bike regulates the voltage to meet the current (amp) demand of the battery. So if the battery is low, voltage will be higher to meet the demand...


Yes, that does appear to be the case. From the schematic of the ST, it appears to use a switched field type of charging system...which essentially means the charging system is turned on and off to regulate the voltage to a constant level, which ends up producing 'just enough' amperage to meet the current demand. It will keep regulating the voltage up to the point where amperage is maxed out, at which time the voltage will start folding back. This why it is important to have an external voltage meter installed (and monitor as necessary) if you have a lot of farkles installed that could potentially exceed the capacity of the charging system.

Edit - forgot to add (in an attempt to answer your original question) - Sometimes, the charging rate is controlled by subtle things such as the resistance of fuses in the circuit. A resistance of a < 50 milliohms is normally not significant in the grand scheme of things; however, it can be significant when coupled with the internal resistance of a battery. The internal resistance of a battery is normally very low (usually on the order of a couple hundred milliohms). As correctly stated earlier, the internal resistance of a battery is lowered as it discharges; therefore, it will demand more of a load from the charging system when it is discharged and less of a load as it approaches full charge. If a fusible link is in series with the battery and the charging circuit (much like Main Fuse B on the ST), it will contain a small amount of resistance...which, when coupled with the decreased resistance of a discharged battery acts essentially as a current limiting device. How much it provides is unknown unless you take some measurements with a milliohm meter and know/extrapolate the internal resistance of the battery.

GlenT
05-09-2010, 01:51 PM
Sometimes, the charging rate is controlled by subtle things such as the resistance of fuses in the circuit.That's interesting. So, if I charge my wife's beemer through the aux power port, the resistance of the fuse in that circuit comes into play, limiting the amount of current going to the battery?

okmurdog
05-09-2010, 02:21 PM
That's interesting. So, if I charge my wife's beemer through the aux power port, the resistance of the fuse in that circuit comes into play, limiting the amount of current going to the battery?

Probably not.

A standard blade type 10A fuse (coupled with a fuseholder) has a typical resistance of ~ 20 milliohms (0.020 ohms). Attaching a charger thru the fuse and to the battery, and a typical worst case start up 'trickle' charge rate of ~ 2A, the max voltage drop across the fuse would be 0.04 volts - not enough to amount to a hill of beans.