Un- plugged Trickle Charger killed my battery !

[ionbeam]

There are battery chargers, trickle chargers and battery tenders. Every company has their own way of doing things so results will vary by manufacturer and model. A charger simply produces a lot of voltage and current to the battery, well in excess of a recommended charge rate. A trickle charger should provide a maximum of 10% of the Amp Hour rating of the battery and reduces the current as the battery approaches 100% charge. However, a trickle charger may still provide a trickle of current even after the battery is fully charged which will eventually cook the battery. A tender can trickle charge, then simply top off a battery as needed and shuts off all current until it senses the battery needs another feeding. Some trickle chargers and tenders also have a special voltage/current profile that can (attempt to) desulfate the plates too.

If you have a '60s era charger it's a brute force design with little sophistication, a late model battery tender will have complex charging controls. I would expect any battery tender to not discharge a battery if left connected and unplugged from AC. All bets are off with a charger or trickle charger.

Adding a diode will probably take care of the unplugged AC discharging in almost all situations. But, I'm not sure that adding an additional 0.4 to 0.7 volt drop after the battery charger's regulation circuit is a good idea. If the charger circuit thinks it's delivering 13.2 volts to trickle charge the battery but your added diode drops the actual voltage at the battery post to 12.6 volts I would expect the battery will not charge the way you think it should. I know that some people will have added a diode and "I have had no problems, it works great" but adding a diode will definitely affect charging voltage if it's added after the output regulation circuit. If you do add a diode, be sure the diode you add has a sufficient current rating.

 

[Old Guy]

Maybe I'm confused -- that sure wouldn't be a first -- but a diode just acts sort of like a check valve to allow current to go in one direction only doesn't it? IOW, to the battery to charge but not the other way when the charger's unplugged.

 

[ionbeam]

Maybe I'm confused -- that sure wouldn't be a first -- but a diode just acts sort of like a check valve to allow current to go in one direction only doesn't it? IOW, to the battery to charge but not the other way when the charger's unplugged.

You are right, a diode is a one way gate or check valve that lets current flow in only one direction. It isn't a free ride though, there is also a forward voltage drop at the semiconductor p-n junction. Depending on the silicon diode type the forward voltage drop will typically be 0.4 to 0.8 volts. Put 13 volts on the anode of the diode, you will get ~12.4 volts on the cathode (band end) of the diode.

 

[Old Guy]

Maybe I'm confused -- that sure wouldn't be a first -- but a diode just acts sort of like a check valve to allow current to go in one direction only doesn't it? IOW, to the battery to charge but not the other way when the charger's unplugged.

You are right, a diode is a one way gate or check valve that lets current flow in only one direction. It isn't a free ride though, there is also a forward voltage drop at the semiconductor p-n junction. Depending on the diode type the forward voltage drop will typically be 0.4 to 0.8 volts. Put 13 volts on the anode of the diode, you will get ~12.4 volts on the cathode (band end) of the diode.

Ah. Many thanks.

 

[audiowize]

Adding a diode will probably take care of the unplugged AC discharging in almost all situations. But, I'm not sure that adding an additional 0.4 to 0.7 volt drop after the battery charger's regulation circuit is a good idea. If the charger circuit thinks it's delivering 13.2 volts to trickle charge the battery but your added diode drops the actual voltage at the battery post to 12.6 volts I would expect the battery will not charge the way you think it should. I know that some people will have added a diode and "I have had no problems, it works great" but adding a diode will definitely affect charging voltage if it's added after the output regulation circuit. If you do add a diode, be sure the diode you add has a sufficient current rating.

The fully charged voltage of the average 12V battery will vary significantly. Adding a shottky diodes with 0.25V of drop at 1A or so isn't going to be particularly destructive to charging.

A "smart" charger might be able to supply as much as 14.5 volts to get the job done.

 

[ionbeam]

The fully charged voltage of the average 12V battery will vary significantly. Adding a shottky diodes with 0.25V of drop at 1A or so isn't going to be particularly destructive to charging.
A "smart" charger might be able to supply as much as 14.5 volts to get the job done.

How many FJR riders know to use a Schottky diode? Even with a smaller forward voltage drop, 0.25 volts can be a lot.

Looking at a standard 12 volt battery state of charge table a small voltage drop can mean a lot of difference in the true state of charge. The state of charge is determined by the specific gravity of the electrolyte and indicated by the voltage.

Man up and build an AC power detection circuit which uses a FET with a very low R DS(on) in place of the diode that will isolate the battery from the charger when AC is OFF

Often this kind of discussion goes beyond what the average motorcycle rider needs to know. I did want to mention that a typical rider shouldn't take just any old battery charger and stick any old diode in series with a charging lead and expect good results every time.

 

[mcatrophy]

...Man up and build an AC power detection circuit which uses a FET with a very low R DS(on) in place of the diode that will isolate the battery from the charger when AC is OFF ...

Or use a relay, mains coil, contacts in series with the charger connection to the battery.
(I'm an ex-electronics enginmeer, I really like your idea better .)

 

[Fred W]

...or maybe just unplug the charger from the battery tender cable when it isn't plugged in to the wall?

I dunno

 

[rushes]

The timers that switch on and off the power with a plug in charger.

Could they be adapted to the power between a battery and a charger instead of the grid and and charger?

Goober minds want to know....

*edit*

power in, power out. Timed.

 

[ionbeam]

...or maybe just unplug the charger from the battery tender cable when it isn't plugged in to the wall? ...

Buying a good tender, disconnecting the battery from the charger when unplugging from the wall, those are hard things to do.

After a couple of mentions of diodes I said that diodes may not be such a good idea, audiowize countered so I put out stinky bait. I don't think anyone was actually planning to do more than adding a bad idea diode

 

[DiggerDr.]

All of this is educational. I'm going with ionbeam on this one. Effective. Simple.

 

[yamafitter]

The Canadian FJR's have an ignition immobilizer circuit that pulls a constant drain on the battery so when my FJR goes in the garage the battery tender gets plugged into the socket I have mounted on the bike. The only time the tender is without AC is during a power outage at the house.

During my days at the Nuke plant I spent many a day doing preventative maintenance on battery banks, UPS and inverters that fed the various backup systems. We could get into long discussions about equalizing vs float voltages and how adding solid state devices affect these voltages but in keeping with the KISS principal, just disconnect the tender or whatever device you are using to charge the battery whenever the device is not powered.

 

[mcatrophy]

The Canadian FJR's have an ignition immobilizer circuit that pulls a constant drain on the battery so when my FJR goes in the garage the battery tender gets plugged into the socket I have mounted on the bike. The only time the tender is without AC is during a power outage at the house.During my days at the Nuke plant I spent many a day doing preventative maintenance on battery banks, UPS and inverters that fed the various backup systems. We could get into long discussions about equalizing vs float voltages and how adding solid state devices affect these voltages but in keeping with the KISS principal, just disconnect the tender or whatever device you are using to charge the battery whenever the device is not powered.

The UK FJRs also have the immobiliser. When I measured the current draw on my '14, it was about 2mA. So, if there was no self-discharge, the time to half discharged would be 12/0.002/2 hours, or 125 days.

The real trouble with the KISS "Disconnect when the AC is off" is that you might not be there when the mains is off (winter vacation in Florida?), or if you choose to use a timer to turn the charger on occasionally. As my son found out.

Best advice is to measure the non-charging leakage back into the tender/charger to satisfy yourself it's not a significant drain. If it's less than a milliamp or so, just let it be. If it's significant, use one of the previously mentioned methods to protect the battery.

 

[RaYzerman19]

...or maybe just unplug the charger from the battery tender cable when it isn't plugged in to the wall?

Using the inverse theory, while battery tender cable is plugged in and plugged into the wall, leave it plugged in when you go on vacation. The Deltran's have the smart circuitry to do just that.

As for when the charger is still plugged into the wall with the battery disconnected, the red light blinks to drive you crazy alerting you to the fact the battery has a fault or is disconnected. Not that I advocate leaving it that way for extended periods of time, but you could if you got lazy and didn't unplug it from the wall.