Battery types for model subs

[corsaire]

Hi Jeff

I have the Graupner SPEED 500 7.2V which I think is too powerful for my Akula, but anyway, I don't run my boats to speed, I only use 1/3 to 1/2 of the power. What gives?

[JWLaRue]

There are several different versions of the 7.2-volt Speed 500 (if you have the model number, we can pin it down exactly)....but if you are using the one that is not the "BB" variant, then what I see from the Graupner specs say that the motor has a no-load current draw of 2 amps and a stall current of 96 amps.

All that said, as I suggested in my previous post you are going to have to do some investigation to identify where the problem lies. Without more information it's going to be hard to help you.

Here's something additional to try: disconnect the prop shaft from the motor and do a workbench run at whatever throttle speed you were using in the water. How long does the battery last?

Also, since you have a basically drained battery now....how long does it take to charge the battery back to full?

-Jeff

[greg w]

Does your charger tellyou how many miliamps it took to recharge the batter? That would give you an indication as to how "much" battery was actually used. You could have a bad battery. a 5500 mah battery draining in 15 minutes indicates a 20+ amp draw

[corsaire]

Interesting enough, it only took less than 20 min to recharge, hmmmm, but now that I think about it while on the pond (a dirty pond at that and full of mud and weed) I had to force the motor a few times at full
speed to get it unstuck, and when I got it out there was some fine weed wrapped around the prop, in between the prop and the stern that I had to unroll. Perhaps that did it. But this is a LIPO I thought, it should last longer regardless. I'll test again and see what gives. It could also be that the battery is not holding full charge, as I learn more about these LIPOs I understand you have to "storage" them through the computer charge or they won't hold charge next time. I'll test it like you said and see what gives, thanks

[JWLaRue]

It's not the battery chemistry....it's the number of mAH. I use a 2200mAH (2.2 AH) battery in my OTW Type XXIII and it runs for several hours!

If it only took 20 minutes to recharge after you used the battery at the pond, then it *might* be the battery.

.....still need more data...

-Jeff

[southern or]

Hi Jeff

I have the Graupner SPEED 500 7.2V which I think is too powerful for my Akula, but anyway, I don't run my boats to speed, I only use 1/3 to 1/2 of the power. What gives?

There are several different versions of the 7.2-volt Speed 500 (if you have the model number, we can pin it down exactly)....but if you are using the one that is not the "BB" variant, then what I see from the Graupner specs say that the motor has a no-load current draw of 2 amps and a stall current of 96 amps.

All that said, as I suggested in my previous post you are going to have to do some investigation to identify where the problem lies. Without more information it's going to be hard to help you.

Here's something additional to try: disconnect the prop shaft from the motor and do a workbench run at whatever throttle speed you were using in the water. How long does the battery last?

Also, since you have a basically drained battery now....how long does it take to charge the battery back to full?

-Jeff

I have a Graupner 500 at 7.2v. I have to ask, are you running direct drive, or a reduction gear? The one I have is a brushed high speed motor and it runs better at higher RPMs so it has a 3:1 reduction gear and on a nicad 7200mah battery it's good for about a half hour to 45 minutes.

It's not the battery chemistry....it's the number of mAH. I use a 2200mAH (2.2 AH) battery in my OTW Type XXIII and it runs for several hours!

If it only took 20 minutes to recharge after you used the battery at the pond, then it *might* be the battery.

.....still need more data...

-Jeff

That's not right. My 6v 7200mah batteries take around 4-5 hours to charge from empty. I have to ask though, you're using a 11.1v battery on a 7.2v motor? That'll burn the motor out causing it draw a bunch of amps at once.

[JWLaRue]

I have to ask though, you're using a 11.1v battery on a 7.2v motor? That'll burn the motor out causing it draw a bunch of amps at once.

It's been my experience that Graupner motors are pretty forgiving in terms of running them at somewhat higher voltages. Perhaps I've just been lucky....

-Heff

[corsaire]

I have a Graupner 500 at 7.2v. I have to ask, are you running direct drive, or a reduction gear? The one I have is a brushed high speed motor and it runs better at higher RPMs so it has a 3:1 reduction gear and on a nicad 7200mah battery it's good for about a half hour to 45 minutes.




That's not right. My 6v 7200mah batteries take around 4-5 hours to charge from empty. I have to ask though, you're using a 11.1v battery on a 7.2v motor? That'll burn the motor out causing it draw a bunch of amps at once.

My Graupner SPEED 500 7.2V (not the fancy ones) came with the D&E Miniatures' WTC (aka subdriver these days), it's attached to the bulkhead to a 3:1 reduction gear.
My power source is a TENERGY LiPo 11.1V 5500 mAh battery pack with PCB. My understanding is that the higher the mAh the longer the running time. Is this correct?
If 11.1V battery is too high for a 7.2V motor, then would you recommend a 7.2V battery or lower?

[JWLaRue]

Have you tried any of the various suggestions already offered to help troubleshoot the problem?

-Jeff

p.s. a 2S LiPo would be a better match, voltage-wise, for a 7.2-volt motor.

[drschmidt]

The voltage does not kill a Motor, it's the current. And wehn your prop is small enough, higher voltages won't result in deadly currents.

[corsaire]

Have you tried any of the various suggestions already offered to help troubleshoot the problem?

-Jeff

p.s. a 2S LiPo would be a better match, voltage-wise, for a 7.2-volt motor.

No, not yet, I ran out of time yesterday, next weekend most likely will put it through the tests. One more thing on LiPos, since these are rather particular type
of batteries, special care required and all that. I've read that for better usage, longer life battery and above all safety is good practice to properly discharge as well
as "store" the LiPo battery, in other words bringing its charge to a safe minimum by mean of the computerized charger, LiPos can't just be put away fully charged or depleted.
Also, "balancing" the battery, the cells rather in an evenly charge. Do any of you "balance" their LiPos or "store" them after every run?

http://www.rogershobbycenter.com/lipoguide/

"I recommend to our customers that they put their LiPo batteries in storage mode after every run. This isn't necessary per se, but it does build up good habits. If you do it every time, you don't have to worry about whether or not you remembered to put it in storage. I have had many customers come to me with batteries that died because they charged it up, intending to use it, but life got in the way and they never remembered to put it back to storage voltage. Lithium-Polymer batteries can be damaged by sitting fully charged for as little as a week. This doesn't mean they will get damaged every time you leave them for over a week. It just means they can, and I've seen it happen. So don't forget to put your LiPos at storage voltage when you're done using them.

They should also be stored in a fireproof container of some sort. As I mentioned above, most people tend toward leaving their LiPos in a LiPo bag, as they are portable and protect your workshop from catching fire should the LiPo combust. I have also seen people use empty ammo boxes, fireproof safes, and ceramic flower pots. Whatever you have (or can buy) that will prevent any fire from spreading will be worth it in the unlikely event that anything untoward should happen.

I feel the need to reiterate: the most common problem people have with LiPo batteries is a direct result of improper storage. When a LiPo battery sits for a long period of time (and not at proper storage voltage), it tends to discharge itself. If it drops below 3.0V per cell, the vast majority of LiPo chargers will not charge it. Sometimes, batteries with this problem can be rehabilitated, but just as often, they are a lost cause. So again: if you take a 'laissez-faire' approach to the storage of your LiPo batteries, it's entirely likely that you will be purchasing new batteries sooner than you think."

[JWLaRue]

I always balance the batteries after a charge. My charger is a balance charger but I find that even after charging the battery still needs to be balanced. I use one of the Astro Flight Blinky LiPo battery balancers. I got mine from Tower Hobbies here:

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXMRZ9

I too have read a lot about storing LiPos in a less than fully charged, but not (fully) discharged state. I've not done much about that to date. It seems I rarely discharged one of these enough to get close to the 3.0-volt near-death state. I have stored fully charged (and balanced) batteries just fine for several months with no apparent issues.

-Jeff

[salmon]

I can argue with Roger's Hobby Center, not from expertise, but from experience. The number one way I have destroyed LiPo batteries is charging improperly. I have and still do charge up my LiPo's and put them away if I do not make it to the pond. I know, gasp. Draining them to I think 1/3 is the storage level, but not all the way down. Since I have learned to charge my batteries properly and not run them too low (which would be my number two reason for destroying my LiPo batteries), I have had no issues with my batteries. I do not want to run down a rabbit hole and take this away from the main issue, which is run time, but what are you charging your batteries on?
Sub-Driver sells a simple charger with no balancing. Is that what you are using?
Another tool I like to use is a battery display that shows each cell's charge http://www.hobbyking.com/hobbyking/s...er_2S_6S_.html
Anyway, going back to topic, if your battery is charging completely, then it is a issue of amps being used and the suggestions Jeff has made are great steps to hunt down your issue. Let us know how it goes.
Peace,
Tom

[southern or]

I charge all my batteries regularly and use a balance charger as well. As for the battery voltage to motor, full throttle sends the most current to a motor unless you have a programmable ESC and put a limit on what is "full power." I've used a 7.2v battery on my 7.2 motor, but I've been using Viper ESCs forever and told the ESC to stop well before full power. Most of the motors I use for my surface fleet are rated with a range and tend to have a cut off of 15v. All those motors are operated on 9.6v supply and do just fine. My Oscar project is designed for a 6v supply, but the motors are rated higher, I just forgot what the cap is for Engel's motors. My Flight II Arleigh Burke has correct to scale props (which are huge) and as a result the motors draw more-but that is a twin ESC boat with 2 5amp batteries. How big is your prop? As drschmidt alluded to, the bigger the prop, the more current is needed to spin it.

[corsaire]

I have a Tenergy computer charger that does all of that: charge, discharge, storage, balance, etc, etc. But my LiPo battery came w/o the extra wires to do a "balance".
For those who their LiPo batteries have those extra wires - how do you waterproof them?