So as the topic says I think there are some issues here and I would like to get another opinion.
At what voltage does the BB2 start acting weird?
Would I greatly benefit from having a 9volt power the logic rather then the 6 volt battery 5x4700Mah cell’s NiMh
It seems like the run times lately have gotten shorter and so have the charge times.
I charge this pack I made at 5amps, the website I ordered the batteries from states that’s an acceptable charge rate although… would charging them at a lower amp rate be better for them?
I tried running a discharge cycle on them and charging it back up again but still seems to do the same thing “not run that long” Granted I don’t charge my battery and run the phoenix until it becomes wobbly and un responsive, but last time i did that i put a volt meter to the battery pack and it was still around 6 volts… so I’m not sure what the deal is.
My experience with NiMH is you should always store charged. But it will self discharge fairly rapidly. If the pack is stored for a long time cells can go dead and even reverse voltage! But it will survive if you do several charge/discharge cycles.
I would never charge a NiMH any faster than 1C unless you’re in a hurry like at a robot competition, or your final presentation at school is due and you forgot to charge the bats. lol
Don’t overlook the obvious. Is the charger working properly?
yeah I’m pretty sure the charger works fine as its charged the batteries before and its new…
I’m guessing that the botboard doesn’t like to operate with a shared power or the servo’s draw too much seems kinda weird… its like within 5 seconds it goes from walking fine to acting like it just got out of tub of 35 degree water all shakes’alot…
I guess my thinking here is I would assume that 4700mah cells would be able to power 18 servos relatively easily now my theory might be truly crushed based off the power requirements of those hitech servos too, which are pretty high…
Probably guessing here if they were 18 Futaba S3004’s that would be a different story, they would probably last 2 weeks.
Both facts have little importance if the charger is not working now
Jittery can also be a sign of operating the servo with too high a voltage. I guess I’d have to see it…
You should be able to power a phoenix for 20 to 30 minutes on a 5amp/hour battery. Hexs only draw around 8 to 10 amps.
Lets chat about the battery itself. You said you made it. Are you using a battery holder, or did you actually solder the batteries together? What sort of wire are you using?
The wire I used was off a power supply I mangled up and it wasn’t a budget power supply either, to be honest I have no idea what gauge the wire is although when I charge the battery and use it a while the wire isn’t warm to the touch so I know its thick enough, although I highly doubt this is an issue… I just think my expectations of how long this should last on the phoenix is slightly longer then I would have guessed.
One thing I do suspect though is the logic isn’t getting enough juice as it just seems like the phoenix just all of a sudden stops and there is still voltage in the batteries … I think I’ll have to measure the batteries with a load on them IE still connected to the phoenix while its on and wobbly and all.
Probably the first thing to test. A poor solder joint or connection in your battery pack could be causing the problem. Trouble shooting with a multimeter while the bot is operating should find a high resistance or if the batterys are not holding a full charge. Binding servos could also cause excessive load on the batterys.
Yeah zoomcat, there is one thing I back about the project’s I do, there is never anything wrong with anything to do with wiring, its always been the thing that I’m most careful with and have never had an issue with anything
I think my expectations on how long this battery pack should last is shorter then I would have liked.
Although I think I should wire up a 9volt for logic and see if that makes it last longer without going all spastic on me when the batteries get low. I’m guessing when the battery pack I made gets low the current draw of the servos causes the voltage to dip below or around 5 volts which causes the BB2 to reset
Yes after seeing your battery I don’t suspect the wires! It looks like you did a good job. I’ve read through these messages and you never really say how long the battery lasts, just that the run times are shorter. What sort of run times were you seeing? How much did it reduce? BTW the 9vdc battery on VL will increase run time.
Probably also should realize that as you cycle the batteries their capacity is going to go down over time. This is caused by several factors but two of the largest contributors will be how well the cells were matched to begin with and whether or not the charger is properly terminating the charge cycle. If any cell in the pack is much above 45C when the charger finishes then it tends to age the cell quicker. Charging is an exothermic process and you can help reduce thermal wear by making sure the cells are not having the airflow around them restricted while being charged.
Robotdude what did you mean by charge at 1C ?? was that 1 amp?
I think I’ll try and charge them slower the cells were getting a bit warm at the end of the cycle charge time at 5amps was around 45 minutes…
Run time actually I couldn’t tell you I haven’t actually been playing with the robot for an hour or 2 its been on 5-10 minutes then off for a day exct so it sits a while in between usage id have to guess probably 45 60 mins ish?
I’ll experiment with trying to charge the pack at a lower amp rate
These are the cells I bought batteryjunction.com/tenergy-sub-c-4700.html they match them before they send them to you, honestly a pretty good deal, the ones I picked up had tabs, I have never really made a battery pack before as I didn’t have a way of charging them or really understand how charging a battery works, but it seems like the max charge rate for those cells is 5 amps… scratch that I just looked at the site again and Apparently I was incorrect in saying 5 amps, it looks like 4.5 amps is the max charge rate… I think I’ll try charging it at 4.5 amps next time and see what happens with the length of the run time and use a 9volt for the logic voltage although where to mount the battery…
Anyway I think the problem I had wasn’t a problem to begin with per say??
In reference to charging rates, ‘C’ is the capacity of the pack / 1H so you get amperes. Thus a 4.5AH pack is said to have a 1C rate of 4.5A.
You will also see charge rates expressed as multiples or fractions of ‘C’ such as a 10C discharge rating or a C/5 conditioning charge rate. Using the previous example capacity a 10C rate would be 45A and C/5 = 0.9A.
When you read 1C pertaining to batteries it means the capacity of the battery. Charging a 1600mAh pack at 1C means you charge it at 1.6amps. I said I never charge NiMH at more than 1C, so for you it’s 4.7amps. However there is no reason to charge the battery that fast if you don’t need to. Remember the comments about at a robot comp, or school project? In other words your batteries will accept more charge, last longer, and deliver more current to your robot if you charge them at a lower rate. Charge them at 2 amps instead of 4.5 amps.
