Can you use RC-2400's for Servo/Rx power???

[buggieracer]

I have a MP and it has 2 Hitec 645Mg servos and even with 1100mah 6v packs the run time is too short.I have a spare Trinity RC-2400 racing pack which i've taken apart and have arranged 5 of the cells different ways and they will fit with my reciever in the radio box.I'm sure this pack will last all day,but are their any risks to the reciever or servos using these on them?Thanks

[Railman]

Absolutely not! The main consideration is the weight, which I couldn't make a recomendation on. As long as you have the right voltage, the extra amp capacity won't hurt a thing. Motors will only use what they can as far as amperage is concerned. Voltage is another story though. Voltage is the pressure that forces the current to travel through electric devices. Joe

[Grant Tokumi]

Railman,
On the topic of amps, you've mentioned in a previous post that a battery's amperage can affect a motor's performance. I remember you using words like "punch" when referring to this. I experienced this years ago when I went from 2 battery packs to a single battery pack for my clodbuster (2 motors). The clod lost some significant "punch" off the line when I did this. I had the understand that a battery will always put out what is required from the motor. And thats why it puzzled me when I lost performance. I thought I would only lose run time. If I understood your earlier post, the battery can be responsible for restricting current to the motor. Like if you hook up 4 motors in parallel to a single 6 cell battery pack. If each motor drawed 25 amps each, I thought the battery would always put out 25 amps to each motor or 100 amps in this case. But that doesn't seem to be the case unless I'm misunderstading something. Care to expand a little more detail about this? What is the term and range for this amperage draw limit? Does it somehow relate to the mah rating (1700 mah, 2400mah, etc) or is it a totally separate thing?

[Railman]

Grant, the simplest way I can think of right now is to compare an AA nicad to an AA alkaline. They are way different animals. An alkaline batt has a very high capacity,& voltage, but does not have the ability to put out a lot of amps. For their size nicads can put out incredible amps, at a lower voltage than alkalines. They still have their limits though. A motor can only draw what a batt will put out & no more...it can't force it out.
Lets look at two different water hoses. If you had a 1" water line at 40psi line supplying a 1/4" hose you would only be able to get x gallons per hour through the hose. The 1" supply line would relate to the batts, & the 1/4" would relate to a motor. The limiting factor is the 1/4" hose. But what would happen if you ran a 1 1/2" hose from that same 1" supply line. The limiting factor would then be the supply line, instead of the hose. In most applications there is not a shortage of current available. However in RC cars there is. It's the batts. The motors are designed to be on the edge of what the batts will supply.
The mah (mili amp hr) rating is a capacity number. It dosn't relate to the ability of the battery to give up amps though. You can have a comparable alkaline batt with the same mah, but it won't put out the amps of a nicad. If however you were powering a low current draw motor, like in a servo, the alkalines would work just as well, & actually better due to the higher voltage. The servo is the limiting factor in this case. A low resistance batt will compare to having a bigger water line supply line. The voltage relates to the PSI pressure that the supply line is. Does this make sense to you? If not ask away & I'll try something else. Joe
;)
edit: at a lower voltage than alkalines. was nicads. :o

[ 08-31-2001: Message edited by: Railman ]

[Grant Tokumi]

Railman, Thanks. I understood your water analogy. Thats what I figured based on my observation with my clod and your previous posts on the other threads. I didn't know batteries also could be the limiting factor for amp draw. So when you have a short, does this mean the battery will still only put out that maximum amperage? What IS this battery amp draw limit? I guess a good assumption is to say one 6 cell pack per motor? I wonder with all these super fast motors that are coming out today, if even the nicads are reaching this amp draw limit. If so, you might get more "punch" if you hook up two 6 cells in parallel huh? And you are saying that a battery's amp rating (1700, 2400, etc) is 100% independent of this amp draw limit right? With my clod, I was actually thinking a 2400 mah battery was exactly like two 1200 mah batteries, so I figured running a single 2400 mah would bring the punch back, but I guess that would be incorrect huh?

[Railman]

Grant, That's right. The mah rating is a capacity number which directly reflects run time. It doesn't reflect how much punch a batt will have. That's a combination of resistance & voltage. That's why racers pay the big buck's for batts that have high voltage ratings at the 30 amp discharge test. At a lower discharge rate, a 20 amp number batt may look just as good as a 30 amp batt, but may or may not act the same in use. That would depend on the use. Joe

[Serius Black]

You CAN run a 5 cell 2400 mAh receiver pack, though I'm not sure why you'd do it on an 1/8th scale buggy. Too bulky. Pick up one of the new NiMh receiver packs, they should last a while, plus they can be charged without discharging them.
Also, make sure you don't have any binding in your steering or throttle linkage. If you, this could drain the battery much faster.
I'm running a sub-c five cell pack on my 1/5th scale car, I've been seeing two to three straight hours of use on one charge. Similar voltage to the smaller cells, just higher capacity.

[Railman]

I just had to clarify my initial resopnse to the question "would it hurt anything to use 2400 batts". I answered "absolutely not" Meaning that it woulddn't hurt anything, & NOT that it wouldn't work. See what double negatives do?!! They should work well except for the weight factor. Joe