Connecting battery & charger to PD board

[Mr Roboto]

My question relates to connecting a "Y" cable to our robot so we can have a battery and charger connected at the same time. we checked the voltage with the charger and battery connected together and just before the charger turned off the voltage went as high as 16.1V. The data for the PD board states "15V max." would the 16.1V damage any components on our robot?

Reference: we are going to have the robot in the hall at school running basic movements throughout the day and want to keep the charger connected for obvious reasons.

[EricH]

How many batteries do you have, and how long does it take to change them?

If your answer to the second question is "less than a minute", you may want to consider just changing the battery. Especially if your answer to the first question is "more than 3".

[jbsmithtx]

Why don't you just switch out batteries periodically? Seems a little dangerous to do if you ask me.....

After all, I don't think the current of the charger can keep up with the current you draw just driving the robot around...

[fb39ca4]

EDIT: Depending on what you are doing, the charger most likely cannot charge the battery faster than the robot drains it, so once the battery is dead, the robot will draw all current from the charger, and overload it.

[Mr Roboto]

were not driving the bot. it is basically a static display. it is going to be roped off at the school running a loop that simply tilts the climbing arms (pneumatically) dwells, extends arms (CIM not under load) dwells, extends and dumps our disc bucket (pneumatically), etc. then dwells for about 5 minutes before it repeats again.

we may program a sensor to activate the loop when someone walks by. so there should be plenty of time to keep the battery charged all day. then fully charged when we turn it off after school.

we just didn't know about the 16.1 volts possibly being an issue when the spec's for the Power distribution Board indicates 15V max.

[cgmv123]

If you want to run your robot off a wall outlet, do it properly and get a 12V 100A* power supply.

*You may need less, but motors suck a lot of power.

[Mr Roboto]

Thanks! I'll check into that.

[EricH]

I think, if that's all you're doing, then you may need to do some further consideration.

1) Will this display be attended? I know you said it will be roped off. However, for safety, I would never, ever leave a live robot unattended, no matter how up on blocks/behind ropes it was. Also, for outreach purposes, maybe having someone there to say when and where meetings are would be a good idea. (If this is at a school, though, that person might have to be a teacher or administrator.)

2) If you're just doing that much with the robot, I think having someone walk by during a passing period to check on the battery voltage should be quite sufficient. The main thing I'd be worried about is compressor draw when it's charging the system; check for leaks before the event or hook some extra tanks into the system so it doesn't have to work as hard and you shouldn't need to be worried about that either.

To be honest, for one motor and the compressor, running every 5 minutes, you do not need a charger connected to the robot. You can have someone who goes by the robot do a quick battery change, and put the old battery on a charger. That should keep you running all day without being concerned about whether or not the voltage from a battery/charger system will fry the PD board.

[fb39ca4]

Originally Posted by Mr Roboto

were not driving the bot. it is basically a static display. it is going to be roped off at the school running a loop that simply tilts the climbing arms (pneumatically) dwells, extends arms (CIM not under load) dwells, extends and dumps our disc bucket (pneumatically), etc. then dwells for about 5 minutes before it repeats again.

In that case, you should be fine changing the batteries every now and then. We get around 20 minutes of straight driving using a single battery on a 4 CIM drivetrain, and what you are doing draws much less current.

[CalTran]

What about investing in a deep cycle battery? We bought two four our demos (during competition these are used for our scouting laptops in stands charging) and we can get a solid 15-20 minutes heavy driving/shooting (rebound rumble style)

[RyanCahoon]

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[Al Skierkiewicz]

Originally Posted by Mr Roboto

My question relates to connecting a "Y" cable to our robot so we can have a battery and charger connected at the same time. we checked the voltage with the charger and battery connected together and just before the charger turned off the voltage went as high as 16.1V. The data for the PD board states "15V max." would the 16.1V damage any components on our robot?

Reference: we are going to have the robot in the hall at school running basic movements throughout the day and want to keep the charger connected for obvious reasons.

Never connect a battery charger and active electronics together. While you measured only 16.1 volts with a meter, a scope might show considerable peaks above that depending on the charger. That is why the robot rules do not allow for this type of wiring.
4.1.8.5 R38
The ROBOT battery, the main 120-amp (120A) circuit breaker (Cooper Bussman P/N: CB185-120), and the Power
Distribution (PD) Board shall be connected as shown in Figure 4-7.

[DonRotolo]

I would shy away from connecting a battery charger to live electronics. A battery can handle momentary spikes, electronics not so much.

A 100A power supply is huge overkill, and brutally expensive.
A 20A power supply would be more than sufficient to maintain the battery and offer some oomph for the robot at times. Just adjust it so the output voltage (unloaded) is not more than 13.7 volts and you'll be fine.

Alternative is a larger marine (deep-cycle) battery, about the same cost as a power supply, might last all day like that.

[EricVanWyk]

I spoke with a friend of mine that used to design battery chargers about this. We looked at three lead acid charger types:

1) Giant Transformer and a Rectifier
Exactly what it sounds like. The voltage is set by the turns ratio of the transformer. The current limit is set by the magnetic paths in the transformer. Good enough for charging a battery, but I wouldn't want to rely on the precision of any specs.

2) Buck Regulator, CC-CV
This looks really similar to the power supplies on the PD, but they accept a much higher input voltage (rectified wall power). It is the gross topology of the 5V regulator, and the over-current strategy of the 24V regulator.

CC -> Constant Current. If the voltage difference between the battery's current state and its desired state is high enough, the buck regulator reduces its output voltage until a given current is produced.
CV -> Constant Voltage. Once the battery is high enough, the current is reduced until a given voltage is produced.

This type is fine to use with a PD as long as a battery is also attached.

3) Buck Regulator, High Frequency Injection
Just like #2, but with additional circuitry that attempts to rejuvenate the battery by hitting it with a high frequency component. This is great for batteries, not so great for the power supplies on the PD.

Do not use this type while attached to the PD.