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Rechargeable 9V Batteries

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Rechargeable 9V Batteries
Posted by ROBERT PETRICK on Tuesday, August 4, 2020 11:50 AM

I have a 100% Digitrax system. I have three UP5 plug-in panels and one UR92 panel. All panels get power from official Digitrax PS14 wall warts.

The instruction manual says something along the lines to leave throttles plugged in when not in use to conserve battery power in the throttles. Is this a good practice? How long can the throttles remain plugged in and left unattended?

I use PowerEx rechargeable batteries. I use them because they charge up to something like 9.6 volts and hold a charge for a pretty long time. Another brand only charges up to 8.4 volts and drains pretty quick.

Also, when the throttles are plugged into the UP5 panels, is there any sort of re-charging going on? Or, is there any danger of over-re-charging? When normally swapping out and re-charging in the PowerEx charging station, I never worry about over-charging because of the built-in protection.

Thanks.

Robert

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Posted by Overmod on Tuesday, August 4, 2020 3:05 PM

You are wise to think about this.  The throttles are set up to 'float' the battery when DC is present, so it either doesn't charge or discharge or is 'float charged' for any internal or self-discharge the battery suffers.

This presumes that the battery chemistry is correct for this action.  Some batteries are not intended for continuous charge, and while modern chemistries are often optimized to allow constant float... some may not be.

At one time there were devices that actively conditioned batteries being 'floated' -- some of the better UPS systems built around AGM or 'gel' cells could have very sophisticated 'expert system' knowledge of the weird details of lead/acid construction and would do different modulations accordingly to keep the battery conditioned.  I do not know what careful attention or circuitry Digitrax provides to plugged-in throttles, but I suspect they will tell you in detail if you e-mail or contact them.

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Posted by RR_Mel on Tuesday, August 4, 2020 3:49 PM

Normally manufacturers use polarity protection on battery inputs to prevent damage from the battery inserted backward.  That is normally a diode and if the Digitrax has a diode for protection that would prevent the Digitrax from charging the battery.

A quick check with a volt meter on the Digitrax battery terminals should tell you if the battery can be charged from the Digitrax.  If you don’t measure voltage on the battery terminals of the Digitrax it should be safe.


Mel


 
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Posted by ROBERT PETRICK on Tuesday, August 4, 2020 4:27 PM

RR_Mel

Normally manufacturers use polarity protection on battery inputs to prevent damage from the battery inserted backward.  That is normally a diode and if the Digitrax has a diode for protection that would prevent the Digitrax from charging the battery.

A quick check with a volt meter on the Digitrax battery terminals should tell you if the battery can be charged from the Digitrax.  If you don’t measure voltage on the battery terminals of the Digitrax it should be safe.

Mel

Hey Mel-

Thanks for the info, but I'm not exactly sure what you mean.

I removed the battery from my throttle and touched the terminals with my little multi-meter. It read about 2.1V, and over a period of about 60 seconds, the reading steadily declined to barely perceptible mV (I took that to be essentially zero). Does this sound right?

Also . . . many years ago at a former club, we had running sessions about once a week, sometimes about once every two weeks. There was a standard procedure at the end of the session to take out the 9V batteries, turn them around, and re-insert them into the Digitrax throttles. The senior members said that was to preserve (non-rechargeable) battery life. I never questioned the practice then, but I never do that now. It's kinda funny that when you own the system, you tend to treat things with kid gloves.

I don't know if the Digitrax info regards only standard (non-rechargeable) batteries. Maybe the instruction manuals were written in the old days when standard batteries were far-and-away the only batteries used, and rechargeable batteries were a little too avant garde.

Robert

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Posted by RR_Mel on Tuesday, August 4, 2020 5:02 PM

If that reading was with the Digitrax on then you should be good to go.  That was most likely a capacitor discharging through the meter.  I use the PowerEX 9.6 volt batteries in several goodies, very good battery! 


Mel



 
My Model Railroad  
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Bakersfield, California
 
I'm beginning to realize that aging is not for wimps.
 

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Posted by Renegade1c on Tuesday, August 4, 2020 6:02 PM

I use these. Keenstone 9V Lithium Ion Rechargable Batteries. The voltages is listed as 6 to 8.4 volts however in my experience with them they stay on the high side much longer than a NiMH battery. Lithium Ion batteries are very good chemistry for electronics as they have a very low drop in voltage until the very end of their charge and then the drop off very quickly. They are also 800 mAH vs 230 mAH for the Powerex cells. 

Image source

While the above image is most likely for a AA battery it shows what I mean by the discharge curve of the battery. As you can see in the green a Lithium battery has a fairly small voltage drop until end of charge. A NiMH is similar but not nearly as good. 

The other advantage to the Lithium Ion is that they pack a long more punch in terms of amp-hours. The lithium ions have at least 3 times the capacity as the NiMH cells. 800 v 230 mAH. 

At any rate I have had very good success with them. 


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Posted by rrinker on Tuesday, August 4, 2020 9:37 PM

 There is zero charging going on in DT500 and earlier throttles when plugged in. Actually, even the new DT602 does no charging when plugged in to a Loconet panel. 

 Personally, I shut EVERYTHING off in the train room when I leave the room - previously everything was powered by a power strip which was plugged in to an X10 module, since I was in a rental and couldn't rewire anything. In my new basement layout area, all the outlets are controlled by wall switches with pilot lights, so I know when things are on. 

 For the older (now meaning DT500 and earlier) throttles, you can roll the battery over - + to -. - to +, to keep it in the throttle but effectively shut it off. There is reverse polarity protection and the battery will only self-discharge in this position. The DT602 actually has a power switch.

 The Maha PowerEx Imedion batteries, like Sanyo (now Panasonic I think) Enloop, have low self discharge, so unlike most other brands of Nimh batteries, they will retain a charge when stored for a much longer time. The 9.6 ones use smaller but one extra cell to get 9.6V instead of 8.4V, the older Digitrax throttles being more sensitive to low voltage, due to (not confirmed - I've been meaning to take apart my DT400) use of a voltage regulator that's not a low dropout voltage device - meaning in needs a fairly large difference between the input voltage and the output voltage to function.

                                       --Randy

 


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Posted by ROBERT PETRICK on Wednesday, August 5, 2020 12:52 PM

Thanks to everyone for the useful info.

I, also, shut down everything on the layout at the end of every running session. There are three 6-plug power strips at three 'corners' of the layout: 1) at the base station for the DCS 210, two SE8Cs, one BDL16, and the UR92; 2) at one 'corner' for two SE8Cs, one BDL16, and one UP5; and 3) at another 'corner' for the DB 210 and two UP5s. I shut down all three in sequence, but there is always a chance I might get distracted or forget one or another.

I don't generally leave a throttle plugged in, but if I ever did, I'm glad to hear there (probably) won't be any damage done. Any throttles left plugged in or unattended would only be powered for an hour or two at the most, and probably more likely only for 10- or 15-minute breaks. At any rate, I think they go into sleep mode after five minutes or so whether plugged or just lying idle on the desk, or even in hand while running.

One reason for this discussion is to determine if I need to install saddles or cradles at every UP5 plug-in port to allow battery-saving convenience, and I think I'll not do that for now.

Thanks again.

Robert 

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