Large Scale Central

Making NiMH battery packs

Electronics Power and Sound
#21

Michael Glavin said:

Devon

You CAN use Li-Po batteries. PCB low voltage is simply a gadget used to help ruin your battery pack and or provide you with a false sense of security. I use Li-Po’s on trains, plains and copters.

And yes there are Li-Po batteries available with PCB’s (slim pickings though) or you can simply use a PCB as an ancillary device or maintain/utilize your batteries correctly and there is no need for a PCB. And there are gadgets available for a couple bucks that plug into the balance pigtail and make noise, flash lights or display voltage telling you when the battery has discharged to the appropriate voltage level, which is long before a battery with a PCB low voltage cut-out takes hold.

That said NiMH will work fine IME, yet you can run these batteries down below safe voltage numbers too, which like other technologies; will eventually contribute to short life cycles. So best case is to monitor your batteries voltage while your running your trains (I alluded to several options above).

Michael

I am not doubting you at all Michael. I just am no battery expert and don’t really want to become one so I rely on guys like you to tell me what I can and can’t do. I have no doubt you can run LiPO. The other R/C guys do it in planes,cars, and boats and we are not reinventing the wheel so I believe it can be done safely. With that said though I don’t want to buck the manufacturer when they say its not set up for Lithium batteries. Now I don’t know why they say that. I trust Tony’s answer. So, could a guy use a Li battery and make it work, probably, but I am not going to be the guy to try. If NiMH works and is recommended by the manufacturer and the retailer then I will go that route. Its just a comfort thing to me.

Now I do have a completely ignorant question for you though. You say to monitor the voltage of any of the batteries I use while running trains. Well how would one do this? I could see it if access were easy and one could stick a volt meter to it and one of my locos I could do this, its a matter of just lifting the coal load. But on my GP/9 there is no easy access to the battery. Hence on board charging jack so I don’t have to remove the battery. So how would/could a person check the batteries? On Li-Ion I just run it til it dies. I mean it goes from running to dead almost instantly (kinda why I like Li batteries). On NiMH I would assume the thing will just become sluggish when it is running out of juice. Is there a better way?

With that said I popped the bonnet on the tank loco and well to my surprise its like a giant cavern in there. I will have no trouble whatsoever fitting everything in there including probably an extra pound of weight. I will be able to make two banks of four cells each in tanks. I am thinking that the ESC and RX will easily fit between the motor and back head. I will put the switches on the underside of the tank. This leaves the entire area in front of the motor for weight right over the axles.

What is the best way to adhere the batteries to plastic, rubber cement/ hot glue? I want to be able to remove them if and when they die so nothing to permanent.

#22

Devon, they make displays that can plugged into the charging jack and will display the voltage. I believe it was Tony that has them.

I secured my batteries, and sound boards, with servo tape. 3M makes a foam tape that is almost the same stuff, but true servo tape is wider and stickier.

#23

I use NiMH batteries in all my engines, but so far I have only had to “split up” one of them into the two saddle tanks on a LGB 2073d 0-6-2 tank engine. I have found that the standard 7.2vt RC car battery to be perfect for my non sound, non RC locomotives. The speed is nice, duration is more than I normally run them 4-6+ hours depending on locomotive and load I am pulling. They are inexpensive and available localy. It helped I had several on hand from my RC cars that are now just shelf queens, along with the proper charger. Mike

#24

Devon,

Tony noted Li-Po’s are not recommended because his ESC does not offer a low voltage warning or cut-off. As you know most Li-Ion batteries are packaged with a PCB, which offers low voltage cut-off and a few other features while Li-Po batteries as a rule are not assembled with a PCB.

In short Li-Po batteries could be equipped with a PCB, yet they don’t find favor do to the inherent shortcomings of these devices. PCB’s are generally offered for low current draw applications say under 6 Amps nominal, said number is well suited for anemic Li-Ion batteries, while Li-Po can be VERY robust. PCB’s generally offer voltage cut-off at 2.5V and are nonadjustable. Herein lies the problem MANY modelers run their trains until the low voltage cut-off is activated. This feature is touted as a safety device and is not defined as an operational device. If the low voltage cut-off feature of the PCB was intended to be an operational device the voltage cut-out would be set at 3.0-3.3V and or be adjustable. Additionally routine and or even occasional running of the battery down to voltage cut-off may cause the PCB to shut down completely requiring a manual reset (you don’t want to go here). Lithium cells; be they Li-Ion, Li-Poly, LiFe or similar ilk do not weather bouts down to 2.5V per cell without severely affecting their life cycle. This is also true of Nickel batteries such Ni-Cad and NiMh, whereas the voltage discharge numbers are different (.9V per cell is the accepted number as I recall) same assertion and or theory has been proven again and again.

Look at the link below, there are many solutions therein to alert you when your batteries have been safely discharged. Some are fixed, some are adjustable, some make noises, some have LED lights, some have LCD displays and some have noise and flashing LED’s and so on. These are designed for Li-Po batteries as they have an additional balance charge pigtail, other batteries such as Li-Ion will require pigtail work or in the case of a custom Ni-Mh battery you’d wire in a balance pigtail at time of construction. In this circumstance with a SMART BALANCE charger you’d have the best battery maintenance system available today!

http://www.hobbyking.com/hobbyking/store/__1230__85__Batteries_Accessories-Battery_Voltage_Indicators.html

I like Velcro, battery retaining straps and or foam rubber cushioning and tie straps. Other than that there are many products which are essentially comprised of similar chemicals which are very much like silicone, BUT are electrically safe unlike silicones. This stuff bonds to almost anything very well. Names that come to mind are Shoe Goo and PFM, and this stuff is relatively fast setting, is durable and removable too! A small amount goes along way, I’d suggest you experiment with a dab of the stuff, secure something wait a day or too and abuse it and then remove the adhesive…

Michael

#25

That all makes sense to me. I will have to play around with and check out the website. This might be a great place for me to start implementing a low voltage detection. I mean I am starting from scratch. And if I can build it better then why not.

I do see what you and Tony are both talking about now when it comes to the Li batteries and the low voltage detection. I am pretty sure my tenergy pack has a pcb on it. If that’s the only issue then see what your saying. Either have a pcb or better have low voltage detection. I get it.

I already ordered the NiMH batteries for this loco but maybe nexttime.

Thanks for all your input.

#26

I bought some battery boosters for $1.00 each They put out 2 amps. I put one in an HO box car with the battery andanAirWire DCC receiver. My testing showed that with 7.4V in and 12V out, the circuit is about 98% efficient.

#27

OK so after looking at the LiPO low voltage alarms I see how they work. Baiscally you plug them into the balance pig tail and they monitor each cell individually and send a warning when any one of the cells reaches the low voltage limit of 3.2-3.3v. So I can see where this would enable one to use LiPO batteries safely.

Now Michael,

How would one run them on Li-Ion or NiMH packs? For example the 8 cell NiMH 9.6v pack I am going to build. How would you wire that up to a balance pig tail so it could monitor it? It can’t individually monitor 8 cells because there are not enough pins also they are preset to a voltage of 3.3 per cell.

Do you buy an adjustable one and have it monitor the entire pack and set it to??? Or do you buy multiple single cell monitors and wire in 8 of them, one to each cell and set it to .9v.

It is straight forward with the LiPO not so much with the others.

#28

On another note, are the balance chargers, when using the balance pig tail, charging each cell individually. I assume on my 4s Li-Ion pack with two wires I am charging the entire unit as if it were one cell.

Whats the deal here.

#29

All multiple cell Lithium rechargeable cells need balancing.

Soft pack Li-Poly packs are removed and plugged into a balancing charger.

The round cell Li-Ion packs we use do not have the demands of high current R/C planes. They generally have protection pcb’s built in (or should have) that do the job of a balancing charger as well as overall output voltage protection. They still need a smart charger to detect through two wires how many cells are actually in the pack.

#30

I can’t completely concur with Tony’s comment on our PCB’s featuring balance charge capabilities. While PCB’s with quasi balance features do exist, they are not common so to speak and I don’t know of any battery reseller/assemblers utilizing any degree of cell balancing (to be fair some may), the reason cost; cost is maybe ten times as much as basic PCB. That said, some PCB’s are offered with “Equilibrium” and others call out BMS, while the majority of what the hobby consumer realizes is a BASIC inexpensive PCB for Li-Ion battery packs.

PCB’s with “Equilibrium” or similar technologies equalize (discharges) the voltage level of each cell to common value after the charge has completed. Charge termination and or individual cell voltage is terminated as whole value (4.2V x cell count, same as basic PCB), the voltage of each cell @ charge termination can be significant (undesirable). There is NO substitute for a TRUE balance charge regimen far as I know. Okay, so the aforementioned “E” type PCB is decidedly better than a standard basic PCB.

Michael

#31

Devon,

PCB’s for NiMh of varying cell counts are available. If it were me a simple system would suffice; a fuse and onboard voltage display for a couple of bucks. Balance charging is atypical of Lithium technology. Your SMART charger will multiply cell count for known discharge voltage termination, good enough for this technology.

Michael

#32

Devon Sinsley said:

On another note, are the balance chargers, when using the balance pig tail, charging each cell individually. I assume on my 4s Li-Ion pack with two wires I am charging the entire unit as if it were one cell.

Whats the deal here.

Yeas, each cell is individually monitored/trimmed while under charge. You are correct, all PCB’s terminate charge upon reaching the cell count multiplier x 4.2v per cell.

Michael

#33

I stand corrected.

The 4s & 5s Li-Ion battery packs the Sanyo distributor in Australia makes up for me have regular pcb’s that monitor each cell, but they are not balancing the cells as they charge.

I am advised by them the more expensive, and considerably larger, balancing pcb’s are not required for our (relatively) low current demands.