Steve, if they are wired in series then what is the problem? The “cells” inside each pack are 1.2 volt cells, wired in series, to make a pack that produces 8.4 volts. That would be 7 cells per pack. As long as the packs are the same rating, then I do not see what the problem is.
David, there are those who are reluctant to trust me with a light switch, which is why I ask.
Steve, when things are in series, then the SAME current goes through all the components in series.
When you have 2 things in parallel, the current splits between them according to their resistance.
In the case of batteries, they have very low resistance, and that resistance can be affected by charge. More importantly, it can vary a bit from cell to cell, so it’s “easy” to have an imbalance.
If you have enough current to charge 2 cells in parallel, and for some reason it all goes through one cell, then you have DOUBLED the current through that cell, that can spell disaster.
Is that helpful?
Greg
Yeah, Greg, that helps a lot. Thanks. On taking another look, I realized the batteries were wired in series. I must a been asleep, last night, after watching a bunch of gas bags bloviate. (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-surprised.gif)(http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-innocent.gif)(http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-cool.gif)
OK the results are in;
At idle (switched on not moving) the loco draws 0.6-0.75A,this will increase when I install a mylocosound card.
Loco alone nothing attached the current draw was 1.6-1.8A depending on the grade.
Loco pulling a load of 3 log wagons and a caboose (approx. half of what I planned to pull with it to make an interesting log train) the current draw was 1.8-1.9A with an occasional peak over 2A on a tight corner.
The run time was the normal 4 times around the loop then a sudden drop in current draw and the ESC warning for low battery flashing (normally do not see this when it when the loco is assembled) and the motor jerking.
Going on what Tony Walsham said about AA NiMH batteries it is quite obvious that I am asking these batteries to do something they are incapable of.
Looks like the next step is Li chemistry batteries (LiPO, LI-ion, LiFePO).
I am going to modify the water tender so that I can gain easy access to the battery so that it will be removable for charging, basically some rare earth magnets on the floor and a steel angle plate on the shell to hold it in place instead of the 2 screws currently there.
I am still wary about charging Li in-situ even though I am fine with doing NiMH in-situ hence the decision to externally charge but that may change in time.
So the last decision is what type of Li battery to use, one for off road RC racers in a hard case or the “Blue Battery” favoured by some modelers in the UK (I have seen one rated at 12V/9800mAH but that is a chinese spec so who knows).
Greg Elmassian said:
Graeme, my repeated admonitions to measure the current is because often a loco can appear to be running fine, while using an abnormal amount of current.
If you have a physical load that takes .6 amps to move, putting 2 motors in the same loco with the same load does NOT pull 1.2 amps total.
This is a common misconception, and I’ve been on forums for years, and it never ceases to amaze me that people will speculate about something when an actual measurement can be made easily.
When you have the actual current draw under load, everything will become clear.
Regards, Greg
p.s. I realize this might read “harsh”… just trying to save you time, and you were sounding a bit frustrated, I’m trying to minimize that frustration.
Thanks Greg the frustration might be a bit of my own making by being too cautious about LiPo batteries and trying a fix that did not work like I thought it would.