HELP!! BatteryMinder question

[edmcm2000]

Hopefully I can get a quick answer on this. Leaving tomorrow morning for 4-5 weeks, possibly longer. Leaving 2020 Prius in my garage. Just connected the new BatteryMinderplus, and then in reading the manual found that in the event of a power failure (or just not plugging in the 120v plug to the unit) it will drain the battery. We are subject to fairly frequent power failures, and I hope to find out how long the Minder could be without power before it completely drains my little 12V battery. Called the Mfg, but can't get them till tomorrow, to late. Any ideas? Thanks in advance, Ed

[Dark_matter_doesn't]

Originally Posted by edmcm2000

Hopefully I can get a quick answer on this. Leaving tomorrow morning for 4-5 weeks, possibly longer. Leaving 2020 Prius in my garage. Just connected the new BatteryMinderplus, and then in reading the manual found that in the event of a power failure (or just not plugging in the 120v plug to the unit) it will drain the battery. We are subject to fairly frequent power failures, and I hope to find out how long the Minder could be without power before it completely drains my little 12V battery. Called the Mfg, but can't get them till tomorrow, to late. Any ideas? Thanks in advance, Ed

You need a high-current diode between the charger + line and the battery + terminal. Anode side of the diode goes to the charger lead, cathode side of the diode to the battery. An alternator rectifier could work.

This will pass charger current Whois the charger is on but block current from the battery if the charger is off.

[Dark_matter_doesn't]

Whoops - "Whois" should be "when"

[edmcm2000]

Originally Posted by Dark_matter_doesn't

You need a high-current diode between the charger + line and the battery + terminal. Anode side of the diode goes to the charger lead, cathode side of the diode to the battery. An alternator rectifier could work.

This will pass charger current when the charger is on but block current from the battery if the charger is off.

Yup, I thought of that, to late tho, that"s what I get for reading the damn manual. If I hadn't read I wouldn't be worried about it. Ed

[Dark_matter_doesn't]

The idiots making the BatteryMinder should have thought of this.

Alternatively, just disconnect the neg lead on your prius 12 V battery if there isn't time to rig the diode & you expect a power loss.

[blueumbrella]

Originally Posted by Dark_matter_doesn't

You need a high-current diode between the charger + line and the battery + terminal. Anode side of the diode goes to the charger lead, cathode side of the diode to the battery. An alternator rectifier could work.

This will pass charger current when the charger is on but block current from the battery if the charger is off.

I have a Battery Minder and would like to get the diodes, but not sure where I would purchase them. Can you provide any more specific information? Are these easy to attach. Thank for your help.

[hotbrass]

How much current is being used when the car is off?

Try a small boat battery charger. They are built for this exact reason, to maintain a state of full charge over a very long period of time while the battery is idle. Plug it in, hook it up, and foget it.

Most are made to be mounted on the boat, but that is not necessary. Wont help at an airport either.

[qbee42]

Originally Posted by Dark_matter_doesn't

Whoops - "Whois" should be "when"

Just use edit to fix your post rather than making another post. It's cleaner and more effective.

Tom

[a64pilot]

I thought sure the Battery tenders had a diode to prevent reverse current. Is your a battery tender model or some kind of inexpensive knock off?
Radio shack should have diodes big enough, I think most battery tenders are around 2 amps max.

[a64pilot]

From battery tenders FAQ.

17. What happens if the AC power is removed from the Battery Tender Plus battery charger while it is connected to a fully charged battery?
If the battery is fully charged, then the Battery Tender Plus battery charger’s green light will be on. Once the AC power is removed from the Battery Tender Plus battery charger, the green light will go out and the charger not have any effect on the battery. The Battery Tender Plus battery charger is protected from reverse current, so it will not discharge the battery. Of course, like we said earlier when discussing nominal voltage mismatches between a battery and a charger, the battery will not be recharged either.

When AC power is restored to the Battery Tender Plus battery charger, it will restart its charge cycle. The sequence of events should go something like this. The red light will come on for a few minutes. Then the green light will start flashing while the red light stays on. The next thing that happens is what may confuse some people who use the Battery Tender Plus battery charger. Remember, the battery was fully charged, so you may ask, “Why doesn’t the green light just come right back on?”

The reason that the green light doesn’t come on immediately is that when the charger first comes on, the battery is sitting there, fully charged, at a voltage of about 12.9 volts. The charger immediately tries to bring the battery voltage up to about 14.5 volts. This takes a finite amount of time, although it should only be a few minutes if the battery is fully charged. Then, when the battery reaches 14.5 volts, the charger will hold it there until one of two things happen. Either the battery charge current will drop to less than 0.1 amp (from an initial value of 1.25 amps) or, if the current does not drop below 0.1 amp, then the charger will hold the battery voltage at 14.5 volts for 6 to 8 hours.

There are a couple of reasons why the battery current may not drop below 0.1 amp. First, on a larger battery, like an automotive SLI battery, the internal losses of the battery may consume more than 0.1 amp. Second, if the vehicle or the system that the battery is connected to has appliances that consume electricity, then that consumption of electricity, coupled with the battery internal losses may very likely exceed the 0.1 amp limit. This second cause is very common and its result is that the Battery Tender Plus battery charger’s timer circuits will be fully engaged. So it will take 6 to 8 hours for the green light to come on. Fortunately, the Battery Tender Plus has the ability to continue to supply its full current even after it has switched over to the lower, float, maintenance charge voltage of 13.2 volts. When the charger turns the green light back on, it also drops its output voltage to this float, maintenance charge level of 13.2 volts.

Note: It only takes a momentary AC power outage to cause the Battery Tender Plus battery charger to reset.