Large Scale Central

Battery won't fit.

Electronics Power and Sound
#21

Don Sweet said:

Steve, didn’t mean to confuse you. These at two examples of battery installs. I only use the rear battery installed. The forward packs are to show that you can fit them in.

FYI , it is two parallel connected lithium battery packs being charged, we are not charging two battery packs in series. It is important that I explain this clearly.

Don

Don, I typed parallel, but for some reason, spell check changed it to series. That’s my story, and I’m sticking to it. (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-innocent.gif)

There are those that say I can’t be trusted with operating a light switch. (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-tongue-out.gif)

#22

OK, here’s my solution, at least temporarily.

I don’t know why I didn’t think of this last week… (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-undecided.gif)

I’m a cheap bast …thrifty. I have several 14.4 volt, 2200 mHa batteries laying around, not earning their keep. So I looked for a spot to stash them. Aha, says I, they will fit inside the fuel tank, with room for a single Aristo weight to hang from the keel.

Red to red, black to black, and they are wired in parallel, right? Two in parallel gives me 14.4 volts, at 4400 mHa.

Not a lot of Watts to start a heavy train, but it will work out for now. 18 v of speed is not a big deal, at least for the present.

I had to spring for a Veterinary bill, because one of our cats managed to injure herself, so cheap is the word of the day. I had to pay that highwayman over $1,000, for a procedure that I could bill a human patient perhaps $300. I’m in the wrong racket. (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-money-mouth.gif)(http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-surprised.gif)(http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-laughing.gif)

#23

Actually charging 2 packs in parallel is the danger, slight differences in internal resistance can direct all the charging current to the lower resistance pack (Ohms law) and overcharge that pack. (too much current)

Series is less of an issue, since all the cells get the same current.

Now this is a bit oversimplified, since some packs have an internal parallel/series configuration anyway.

Greg

#24

Greg Elmassian said:

Actually charging 2 packs in parallel is the danger, slight differences in internal resistance can direct all the charging current to the lower resistance pack (Ohms law) and overcharge that pack. (too much current)

Series is less of an issue, since all the cells get the same current.

Now this is a bit oversimplified, since some packs have an internal parallel/series configuration anyway.

Greg

Two well respected, experienced people disagree with each other. Great! (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-tongue-out.gif)

#25

Steve and Greg, I am only referring to the lithium packs I sell from MTO. These packs will charge properly due to the PCM board in each pack. As the packs charge and one finishes before the other, the charger will continue to charge as the first pack PCM board prevents overcharging. When the second pack is charged the charger will turn off. If MTO did not warranty the packs I would never suggest it.

Steve are you completely baffled?

Don

#26

Ahh, with packs with smarts, if they have the right smarts they can limit the charge current too.

Dunno if these packs have that protection. Just shutting off when full does not mean it is protected from over voltage or over current while charging.

Normally the PCM board just protects from overcharge and undercharge.

Not that what Don says is impossible, but I think it’s not the norm with those little charge boards.

Greg

#27

Two 14.4v 2200mAh batteries nets 4400mAh as Steve noted and can provide approximately 8.8A under load @ 14.4V (two times cell capacity is typical) for maybe twenty minutes or so in my experience before voltage degradation ensues. Yet, the discharge current is limited by the PCM in play, discharge current values run the gamut based on cell/battery voltage and chemistry.

I’m with Greg, the basic PCM’s typically incorporated in Lithium batteries simply disconnect the charge power source when the VOLTAGE reaches 16.8V (4.2V per cell). Similarly when voltage decays to 9.6V (2.4V per cell) or so the PCM opens the circuit to disconnect the load. And charging at elevated current levels is not monitored and or controlled either. No real SMARTS, just basic charge/discharge voltage and discharge current limits. There are truly SMART PCM’s out there, but they are uncommon in the battery assembler resale market IMO.

I don’t think its prudent to charge batteries in Parallel! You omit the individual batteries response to the charge algorithm in play. Averaging the voltage of said batteries in parallel and asking the PCM over voltage safety to unload the battery(ies) is undesirable IMO.

I use Li-Po batteries in parallel in several circumstances, I simply charge them individually allowing each battery to work in concert with the charger!

Just a reminder, charge your Lithium batteries as frequently as you like. Do not deep discharge the batteries and or allow the PCM to shut the battery/engine down, this is the worst case scenario for extended battery life.

Michael

#28

Don, would 2 of the TRAIN 15 packs, 1 X 5, fit in the fuel tank? Would there be enough room for the single weight?

#29

Steve, Yes and No. Both packs will fit if you remove all the weights and separate the tank to place them inside. The other option is the two packs that will fit mounted inside the shell behind the cab. You can easily Velcro two packs there.

FYI for the techies. RCS of NE sells lithium packs made by MTO Battery that meet exceptional performance and safety standards issued by the military. My battery packs used in our trains take advantage of using these military grade matched cells. Way overkill for running trains but they are more safer and reliable for the long term. These cells have less than .1% difference in internal resistance between cells. We use the more expensive next generation Protection Circuit Module which adds direct short protection and then will reset after the short is removed. No more returning ruined lithium battery packs.

MTO battery does some unique stuff. They have a patent protection circuit for the underwater car battery. They perform testing for companies to get their battery products certified. Segway rebuild battery maker. All cells are bought directly from the manufacturer no distributors. All packs are assembled and tested in York, PA. As of today the preferred cell is made by Panasonic.

Don

#30

Don not to belabor the point, but while matched cells help a lot, and quality cells even more (in my opinion), it still does not eliminate the issue.

The problem is as Michael and I stated.

Break it down to simplicity, a charger for 2 packs needs double the current as when charging one pack. With large packs and high charge rates, the chance for imbalance grows.

Since batteries are very low resistance, a very small difference between 2 packs can yield a pretty large imbalance between current flow.

So, if you are not charging at C, i.e. less than C, my opinion is you are probably ok with the quality you have, but users should check periodically. Higher than C, well I think all bets are off.

There is no mechanism in your packs to detect imbalance or protect from it.

So, after all that, do you charge at more than C or less than C or at C?

Greg

#31

Ummm, Greg, for those of us who are part of the great unwashed, what is "charging at C?"  

#32

Was waiting for the comeback from Don… pretty key point…

Not trying to give Don a hard time, but just using quality components does not allow you to violate ohms law ha ha!

And I really want to know what Don’s stance is, and how he sells his chargers matched to his battery packs.

Greg

#33

Greg Elmassian said:

Was waiting for the comeback from Don… pretty key point…

Not trying to give Don a hard time, but just using quality components does not allow you to violate ohms law ha ha!

And I really want to know what Don’s stance is, and how he sells his chargers matched to his battery packs.

Greg

And the answer is???

#34

will be calling you on the phone.

Greg

#35

You can wire two separate lithium battery-packs in parallel, but they will never perform as one complete battery-pack. They will always be two separate packs at there initial voltage and current rating. (IE) two packs rated at 14.8V @ 2200mah will be one pack at 29.6V @ 2200mah. If both packs are manufactured as two separate packs with two separate PCB’s (for protection from over-charging and over-discharging) they will only achieve their initial current rating. It would better to use each pack separately, then when the first pack dies you switch to the second pack and continue running. The only way to add more runtime to your lithium battery-pack, is to have another row of cells welded in parallel!

#36

Rick

Reading through your post confuses me… Your describing batteries used in parallel, yet your suggestion that the voltage/capacity will be 29.6v @ 2200mAh is incorrect for paralleled batteries, yet accurate for two 14.8V batteries wired in series. I believe you understand two batteries wired in parallel nets single battery voltage but multiplies the capacity by a factor of two (as you correctly suggest adding a second row of cells to a given battery pack will increase run time) . In Ricks circumstance; two 14.8V batteries wired in parallel would net 14.8V @ 4,400mAh.

Michael

#37

Rick, I am with Michael. You math is for series, not parallel.

Just for those following in the audience. Series is wired end to end. Parallel is wired side by side.

#38

I understand what you guys are saying (I have wired many lithium packs in series and in parallel) but there is no way to wire any PCB manufactured lithium battery-pack after the fact. So, your really not gaining any additional amp hours, what happens is you are basically doubling the voltage; whether you think your wiring two packs in parallel or not. Then after about the fifth cycle or so, one pack starts to charge the second pack and the cells become out of balance. So now you have a cow and a calf. The calf will never achieve peak voltage and the amp hours will slowly dissipate.

#39

Actually, if only one pack was contributing at a time even though in parallel (wrong) you still get the amp hours of two packs added.

No matter how you draw it, both at the same time, 50-50 or whatever combination, the sum total of 2 packs in parallel gives you double the amp hours of a single pack.

In reality you also get that in series, but double the voltage could give you some issues if you overvoltage the ESC.

Amp hours is capacity.

Just like if you have 2 one gallon containers of water, no matter how you drink it, you still get 2 gallons.

Greg

#40

Wiring two separate packs in parallel is not only do-able, it is easy peasy.

As I see it there are two reasons why you would want to wire two packs after the fact in parallel.

  1. To enable higher current consumption.
  2. To extend run times.
    Two separate packs (each with a suitable pcb) wired in parallel, should each be diode protected on the output. That prevents one pack backfeeding into the other.
    The packs need to be the same chemistry, same voltage and same capacity.

The diodes need to be able to handle the current. Like this;

Each pack is charged separately via the DC coax jacks on either side.

I use 3 amp Polyswitch fuses. If one Polyswitch trips, the other will follow suit as it cannot handle 6 amps on its own.