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Thread: Desperately need help with 9V sfe batteries am going "Nuts"!

  1. #1

    Question Desperately need help with 9V sfe batteries am going "Nuts"!

    After 10 yrs. my electronic Safe lock gave out i had a locksmith install the new highly touted Amsec ESL 20 lock and it worked fine for 3 months then nothing, locksmith said replace batteries and all is well, but didn't open safe much and 5 months late same issues now with summer here I shoot a lot and open safe 10X daily and after a week batteries are weak and just don't have the power to open lock.

    Now I only use Duracells and they show 9.57V and find out I get 50-60 openings then acts up and will open usually on 2nd try and 30 attempts later nothing and need replacing, safe takes two 9v and on each set I have to replace show 9.37V next batch 9.42V an last set 9.48 and none of these have enough juice to open safe.

    So this gets expensive and rechargeable batt. not recommended since they only get to 8.7 volt and the amps are not high enough.

    Lithium 9v are slightly wider/thicker & wont fit some gadgets!

    What can I do?

    Thank You!

  2. #2
    Join Date
    Jan 2014
    Blue Ridge Mountains, VA

    Default Re: Desperately need help with 9V sfe batteries am going "Nuts"!

    I've been using the Ultralife 9 volt lithium batteries and they work well.

    As for fitment, mine go into a handheld light meter that uses part of the door cover to push the battery to make contact. Absolutely no problems.

    Your other option is to purchase a battery tray for 6 AA batteries and wire your own connector. I'd still use a lithium primary AA battery though as alkaline batteries puke when you least need problems.
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  3. #3
    *Flashaholic* Lynx_Arc's Avatar
    Join Date
    Oct 2004

    Default Re: Desperately need help with 9V sfe batteries am going "Nuts"

    I would be tempted to hook up a 12v power supply and a variable resistor along with a voltmeter and crank the voltage down to 9v and try it and keep cranking the voltage down till it doesn't work to see the actual voltage needed. I would also measure the current draw under operation at 9v. This could give you ideas of alternative batteries. It may be that an 8.4v external lithium ion pack would suffice and even though the initial cost would be greater it could save you time and money on batteries over the years and make for not having to bother with batteries for a long time. They do make lithium ion 9v batteries also but I don't have any experience with them at all so I cannot recommend them but they could be an option to check into.
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  4. #4

    Default Re: Desperately need help with 9V sfe batteries am going "Nuts"!

    I would say something is definitely wrong with your safe lock. This is not normal behavior at all.

    By what you say you get less than 100 openings from a new set of batteries. Every opening/closing would normally take a bout a second. Thus, you are talking about 200 seconds of operating time total. Standby current draw should be negligible.

    9V batteries are usually designed for low current draw: about a few hundred milliamps max. Assuming a high number of say 300mA, 200 seconds of operating time give you about 17mAh. 9V alkaline batteries are usually rated around 500mAh each, so two give you about 1000mAh (assuming parallel connection). In short, you are using a minuscule portion of the batteries capacity before the lock stops working. This calculation, though extremely rough, is supported by the data you gave. Indeed, the batteries voltage barely dropped, and all stayed above 9.35V (with no load) when they stopped operating the lock, indicating that they were all still maintaining most of their capacity.

    9V batteries maintain a voltage above 9V for a very limited part of their capacity. If you look at discharge curves you will see that the voltage drops below 9V usually when less than 5-10% of the rated capacity is used up. When exactly this happens depends on the battery and the current draw. Usually, the higher the current draw the drop to a given voltage will occur for less mAh used. The rated capacity in mAh is usually stated assuming operation down to a cutoff voltage well below 9V (usually around 6.6V, or even lower). In other words, a circuit that expects a 9V battery to stay above 9V is either faulty or extremely poorly designed. In fact, I have never ever seen a circuit that expects a 9V battery to maintain voltage above 8V, and even this expectation is a very poor design choice!

    My conclusions from the above are that one of the following holds:

    1. The lock is defective and should be replaced.

    2. All your batteries are from the same defective batch: they have very high internal resistance so the voltage stays high, but they can no longer supply the required current. This is easy to check by measuring the short circuit current of these batteries for a second or two (this is not dangerous, nor will it harm your meter if put in a 10A range or higher).

    3. The lock is very poorly designed and expects the voltage to remain high (say over 9V under load). In this case trying a rechargeable 9V li-ion based battery may actually work fine for you. These cells house a single Li-ion battery (3.7V to 4.2V) with a boost converter that steps the voltage up to around 9V. The advantage is that the boost converter keeps the voltage constant as the lithium cell gets depleted, and thus you have 9V for the full capacity of the cell, not just for 5-10% of it. As far as I know, some of these cells are of exactly the same dimensions as an alkaline 9V (though I cannot offer a specific recommendation).
    Last edited by ben65; 03-09-2020 at 05:48 AM.

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