RBA84

I just purchased from Amazon.com the Duracell 2 amp battery maintainer ($19.95) and hooked it up to my 87 928 last night. I used the cigarette lighter adapter and immediately noticed the fan went on at its low speed setting (the fan is always on when the car is running). Afraid I would eventually burn out the fan motor, I connected it to the front battery posts.

I thought the battery was at least 90% charged when I connected the maintainer, but after charging all night the red light was still on. I hooked up my battery charger at 10 amps to read the level of battery charge and it read higher than it had before - above 100%.

I checked the output voltage on the Duracell charger and it was about 20 volts (I thought it should be 13-14 volts).

My questions:

1. Can I use the cigarette lighter connection? I don't want to risk buring out my blower motor

2. Is the maintainer working properly? Will the charge light go out eventually? I don't want to overcharge/ruin my new battery, but I need a connect and forget it maintainer - not one I have to discconnect to avoif overcharging. The manual says it will not overcharge the battery - but WHEN will it switch to maintain from charge? I don't want to risk a ruined $135 battery to find out.

Thanks very much for your assistance.

Dr. Bob (the other one)

dr bob

The cigarette lighter socket is not connected to the battery with the key off. If the maintainer really does put out 20 volts, don't EVER connect it through the lighter socket. Late LH controllers will complain (read: fail) if they are exposed to that voltage.

Use a volt meter to watch the charging voltage where you've connected the charger at the jump posts.

On the charge level--

Lets say that your battery was at 80% capacity when you started charging it. It might have 75Amp-hours capacity (see label on the battery) when new. Your old battery charger "measures" the battery terminal voltage, not a great way to tell how well the battery is charged or holds a charge now. But for grins let's say the battery is down 20% on capacity. 20% down means that you need to add another 15Ah. ASSuming that the new charger is actually charging at 2 amps, it will take AT LEAST 7-8 hours to restore the lost charge. That time needs to be discounted for charge efficiency (let's say that's 80%) so we are now at somewhere around 10 hours minimum.

Put a real volt meter on the jump-start terminal and ground, and see whan the actual charging VOLTAGE is. Likely it's mid 12's to start, and goes to high 13's or even 14 before the maintainer cycles off, but no more.


dr bob

The other other one

RBA84

With the maintainer connected to the battery on my RX-300 it reads about 13.5 volts at present and my guess is the battery (not on the 928) is not yet fully charged.

928 started right up with a high cranking speed (higher than I had experienced before using the maintainer last night) - LH was not damaged (whew!!). Not connected to the battery the output from the maintainer does, in fact, read 20 volts. When I connect it to the battery on he Lexus the voltage reads 13.5.

Is there a problem with my maintainer? If the red charge light does not go off in another 4-6 hours or so does this mean the maintiner is defective? What about in 24 hrs?

I assume I can forget about hooking the maintainer up to my cigarette lighter in my 928. Am I correct?

Thanks very much - I want to be able to hook this up to my 928 and forget about it for a week or so at a time. Is the key issue that the red charging light goes off eventually? I do not want to ruin and expensive battery just to find out I have a faulty maintainer.

borland

It is a three stage charger/maintainer, so you should monitor the charging voltages while charging to see what stage of the charging is in effect.

http://www.duracellpower.com/documen...ll-charger.pdf

The float stage on this charger is not a true float, but cycles on and off to simulate a float. It may take more than one day for it to reach steady state fully charged due to the low rating (2 amp), but that should be more than adequate since your likely to be maintaining the battery state at fully charged.

RBA84

If I understand you correctly you are telling me to ignore the 20 volt output when it is not attached to the battery (the product spec. says 14.4 volts output I believe) and wait at least 24 hrs and see if the red light turns off and then cycles on and off? I just want to be sure I am not going to damage my battery with an overcharge due to a defective product. I can check the voltage at the terminals every few hours. Are you saying that as long as it does not rise about 14 it is working O.K.?

Sorry I am so slow on the uptake - I just don't understand the 20 volt output measured by the same voltmeter that shows 13.5 volts when connected to the battery.

Alan

Read again what Dr Bob said - you weren't actually connected to the battery - so if it started up better today - either it was a coincidence or wishfull thinking...

Don't use the cigar lighter - it won't work - but can cause damage - the the fact that the light goes on when connected means nothing - you are just powering things that should be off with the key out...

Your blower motor is the least of your potential problems with this ...

Alan

borland

Yes, its working fine as long as the charge light cuts off at 14.4 volts.

What you'll likely observe, is when the charger is charging at 2 amps (constant current charging), the voltage will rise to 14 volts. Then the charger will maintain that voltage (constant voltage charging) until the current drops to some level (fully charged). Finally, the charger will switch to float mode where it will cycle (voltage between 13.5 and 14 volts) to maintain the full charge state.

Hope that helps.

RBA84

Thanks very much. Is the 20 volt output from the maintainer when not connected to the battery irrelevant as long is when connected to the battery it stops charging at 14.4 volts read at the battery?

I had the maintainer connected to the remote starting post under the hood overnight - not the lighter. The engine definitely turned over faster than it did prior to the overnight charge.

I will stay away from the lighter and connect under the hood from now on.

Bilal928S4

Make sure that the hood light is off when you are charging.

borland

I wouldn't worry about the 20 volts provided you only connect to the jumper post or directly to the battery. Your unit is designed to detect reverse polarity and short circuit, so it may not be able to put out 20 volts with any load.