Operator's Interface: USB Chicklet + Battery

[morpheous115]

Operator's Interface: USB Chicklet + Battery

On the operator's interface for my team's robot we are going to end up using two joysticks which connect through the USB Chicklet.

I have looked through the rules and am not completely certain about if I am allowed to have two extra batteries to power these devices since I have two. Can I use two batteries total? Do I have to connect each battery to each USB Chicklet or can I wire the batteries in parallel?


-morpheous




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[whytheheckme]

You can just use a backup battery, or some other 7.2-12v battery, and most certainly can use it in parallel. The load on it is not big at all. Just remember to charge the battery when your OI is in the pit!

Jacob

[Pavan Dave]

Yeah, you're just fine from what I understand in the rules.

Originally Posted by whytheheckme

You can just use a backup battery, or some other 7.2-12v battery...

12V? Is that what functionally identical is supposed to mean? I had a disagreement with someone about this issue just last week and claimed that ONLY 7.2V batteries could be used.

Originally Posted by GDC - The Robot

<R106> Devices connected to the joystick ports of the Operator Interface via a FIRST-approved
USB adapter (the only approved USB adapter is IFI Part Number USB-CHICKLET) are
excluded from Rule <R105>. If used, this USB adapter must be powered with a 7.2V battery
functionally identical to the back-up battery. Power from the competition port or any other
source shall not be used to power the USB adapter. The USB adapter must be positioned
within the OPERATOR CONSOLE so that the indicator lights may be seen during inspection
and operation in a MATCH.

[RyanN]

Without the rules, yes, it is okay to run it from a 7.2V battery up to a 12V battery:

Power Requirements 7.2 - 12 Volts DC
Maximum Current 500 mA maximum

Those ratings are from ifirobotics.com (http://www.ifirobotics.com/usb-chicklet.shtml)

But apparently from the rules aspect, this is prohibited, so I would stick with a 7.2V battery like the GDC says.

The question remains... What is functionally identical??? Does that mean, identical to the one included in the KOP, or just another 7.2V battery that you can buy from a store, since that can be used on the robot instead.

[whytheheckme]

Originally Posted by RyanN

Without the rules, yes, it is okay to run it from a 7.2V battery up to a 12V battery:


But apparently from the rules aspect, this is prohibited, so I would stick with a 7.2V battery like the GDC says.

The question remains... What is functionally identical??? Does that mean, identical to the one included in the KOP, or just another 7.2V battery that you can buy from a store, since that can be used on the robot instead.

Ah yes Pavan, I didn't check the rules. I was just reading the manual for the chicklet earlier today, and noticed the spec. Thanks for pointing this out.

As for "functionally identical", they mean a set of NiCd(yes?) batteries that provide 7.2V output. The ones we ordered off of Digikey are in a different configuration (a long skinny tube of 3x (two across)), and they never gave us a problem about it.

Again, sorry for the misinformation. It will work, however, with up to 12V. Just maybe not legally.

Jacob

[Al Skierkiewicz]

Originally Posted by whytheheckme

You can just use a backup battery, or some other 7.2-12v battery, and most certainly can use it in parallel. The load on it is not big at all. Just remember to charge the battery when your OI is in the pit!

Jacob

Jacob, the answer to this would certainly be a big No! Batteries in parallel need special handling in order to work properly. There is no substitute for a fully charged battery, charged by a commercial charger in the pit.

As to the original question, the Backup battery capacity is 700 maHr according to the IFI Parts list. You can purchase other 7.2 volt batteries that have higher capacity.

[WaterFreak]

ONE CAUTION............

If the voltage on your battery gets LOW, you will start to get strange and whacky values from whatever input device you are using.

[whytheheckme]

Originally Posted by Al Skierkiewicz

Jacob, the answer to this would certainly be a big No! Batteries in parallel need special handling in order to work properly. There is no substitute for a fully charged battery, charged by a commercial charger in the pit.

Al, I'm not sure that its a problem to put rechargeable batteries in parallel. Remember doing that electricity demonstration in 2nd grade, where putting 9volt batteries in parallel makes the flashlight last longer?

The only reason you may not want to do this is because if the batteries are at different voltages, they may try to charge each other, which with conventional batteries could be a problem, but with rechargeable batteries should be no issue.

Jacob

[Al Skierkiewicz]

Jacob,
When you put two batteries in parallel, the higher voltage battery will pass current to lower voltage battery. A 9.001 volt battery will attempt to push current to a 9.0001 volt battery. As the higher passes current to the lower, it's terminal voltage falls and the process reverses. As this occurs the batteries end up draining each other until there is no more current to be had (domino effect). The only way to prevent this is to use diodes in series with one of the leads (usually the positive). The diodes prevent current from entering the battery but will allow both to supply current to the load. As batteries increase their current density this becomes an additional problem. Our robot main battery for instance could self destruct if placed in parallel with another battery. NiCad and NiMh batteries suffer this as well. Batteries are OK to wire in series but not in parallel.

[Mike Copioli]

Hi Al, I'm gonna have to disagree with you on that one. I assemble 20 amphour NIMH packs for our DPV (dive propulsion vehicles) I have not had one issue with placing cells in parallel. The packs often sit unused for months, still no issue with self discharge other than the standard self discharge rate on NIMH. I perform minimal cell matching proir to assembly and still have had great results. I do the same with our Lion packs. We have had no instances of self discharge. In fact one technique used in cell matching is to place all of the cells in parallel and let them "Equalize". I have used this approach many times and have not had one single issue. Just my thoughts

See you at great lakes.

[Al Skierkiewicz]

Mike,
What voltage are the cells you are using? Everything I have read says this is bad practice and our engineering discussion at lunch this afternoon centered around this as well. Everyone agreed the batteries will self discharge
We are not attending Great Lakes. We will be at Chicago and Boilermaker while I will Lead Inspect at Minnesota as well. Then on to Atlanta.

[Mike Copioli]

The packs are 24 volt 20 amp hour. The cells are 1.2V 10 amp hour cells. there are 40 cells total in series parallel. The Lion packs are 3x 3.6volt 2600mAh cells in parallel placed in series with three alike banks to equal 11.4v at 7.8 Ahr. We have been doing this for years without any issues. I know paralleling cells is an accepted practice. My truck has two lead acid batteries in parallel without any diode protection. Electric vehicles have several batteries in parallel and series. Our defibrilator packs are series parallel even my Lion laptop pack is series parallel. As long as the cells are of equal amphour rating there is no issue with placing them in parallel. They should be matched prior to assembling them but this is not required so long as the weaker cell is not overdischarged. We use a low voltage cutoff switch to ensure that the NIMH cells do not become over discharged and possibly cause cell reversal. Al Check out this link http://www.batteryuniversity.com/partone-24.htm

[seg9585]

I'm not an electrical engineer, but I would imagine that the higher-voltage battery would supply back-current to the lower-voltage battery, thus charging the lower voltage battery until both are at equilibrium. During this process a bit of charge would be lost due to the battery's internal resistance, but this would be a converging process, not a "domino effect".

Batteries are setup in parallel all the time. I am an RC plane hobbyist and it's done to increase the charge capacity to get a longer flight time.

[Mike Copioli]

Originally Posted by seg9585

I'm not an electrical engineer, but I would imagine that the higher-voltage battery would supply back-current to the lower-voltage battery, thus charging the lower voltage battery until both are at equilibrium. During this process a bit of charge would be lost due to the battery's internal resistance, but this would be a converging process, not a "domino effect".

You are correct, that is what happens. Think of it as two pressure vessels placed in parallel. One that contains 2000# of pressure and one that is empty. If both cylinder have the same liquid volume they will "equalize" thier pressure until each cylinder has the exact same volume. In this case the end pressure would be 1000# You will get some unequality at first due to a temp drop in the supply cylinder and a temp increase in the cylinder being filled but in the end the temps will stabilize and every thing will be in equalibrium. This is an analog to voltage and amp hours. Where the difference in voltage would be the pressure difference and Amp hours would be the volume of the cylinders.

[IndySam]

Originally Posted by Mike Copioli

You are correct, that is what happens. Think of it as two pressure vessels placed in parallel. One that contains 2000# of pressure and one that is empty. If both cylinder have the same liquid volume they will "equalize" thier pressure until each cylinder has the exact same volume. In this case the end pressure would be 1000# You will get some unequality at first due to a temp drop in the supply cylinder and a temp increase in the cylinder being filled but in the end the temps will stabilize and every thing will be in equalibrium. This is an analog to voltage and amp hours. Where the difference in voltage would be the pressure difference and Amp hours would be the volume of the cylinders.

Great explanation, thanks Mike.