Dev,
Your last post is kind of confusing. Can you describe exactly what your plan is? Your link above doesn’t work for me so I was not able to review your design.
Lenovo G and Z series (maybe more) have the same power adapter as the classmate so we just always plug into the field with the provided power.
Why all the fuzz about spending lots of money buying batteries and inverters? Why not just buy a spare battery for the laptop? So you always have one charging in the pit. Better yet, in addition to a team laptop, one of our students has his private laptop installed with everything including Wind River, driver station, dashboard, and all updates. We have peer-to-peer source control. Whenever we make changes, we push the code to a USB flash drive, so it can be pulled by the other laptop. It actually saved us one time when the team laptop’s network was malfunctioning. We just transferred the code to the other laptop and ran with it for the rest of the competition.
Yes. Great idea. Why did I not think of that? A solid state relay could support a higher current throughput, getting less toastier. Also, I have already figured out the voltage level conversion for the chips. A backwards zener diode, rated at 3.3 volts will regulate the voltage, bringing it down to roughly 3.3 volts.
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After making the changes that I am working on, It seems that it won’t be way too heavy. Maybe 100 pounds max without the batteries. There will also be castors for it to move on. During transportation, the driver station and the car battery will be removed. Also, no battery will be present at that time. The carry weight should then be pretty low.
We used a deep cycle boat battery attached to an inverter last year. We also used it to charge frc batteries while moving. A deep cycle will last much longer than a car battery as they are built to be discharge fully and recharged unlike a car battery which is being topped up by an alternator.
It was approved but we were told that we had to make an enclosure for the battery to help prevent shorts and spills. We encased it in a vented MDF enclosure (not the safest thing but it did the job). We lugged it around in on our cart during queue and then it was carried by our driver to the station. It was super heavy but we only charged it once or twice a season.
This year we’re using a 11.1v 60AH lithium battery I made myself from recycled makita packs which is muuuch lighter and 1/2 the size but about 1/2 the capacity and a bit more expensive. It can be brought on a plane if you tape the contacts and you seal it in a bag.
Marcus et al,
I have to say that I am concerned about having inverters on carts where no safety ground exists. A simple inverter for a laptop power supply on the surface should not be a problem if all devices are functioning normally and are fully insulated. However, with the lack of safety ground, the potential for contact with exposed metal parts on the robot cart does exist. I must warn everyone that 110 volt wiring can be lethal and should only be considered when under certified electrical supervision.
While it is a risk we have some precautions in place in case of that. Are entire cart a driver station board is wood and the inverter is fused in case of a short. One of our mentors is also EE and a certified electrician.
Wood can make a suitable conductor. Even paint can contain additives that conduct. Fusing only protects the wiring.
Do you have the same concerns about automotive voltage laptop chargers and a battery charger based on a DC/DC converter topology? In that setup there is no 110VAC.
I am not making light of this concern. Even a car battery can give you a nasty burn. In fact in my experience -48VDC DC power sources tend to make some of the worst burns if they can find a path of conduction.
If we use a car battery or a deep cycle battery, we will enclose it with a thin layer of ABS. I believe it is quite acid resistant and we should smell the sulphur before anything bad happens. Also, I am trying to eliminate most of the wiring by placing it on PCB.
Dev,
Acid spills are almost the least of your worries. Hydrogen gas buildup, is a big issue in addition to a litany of other things.
I agree with that. Do you by chance know how to get rid of this H?
By the way, why use a deep cycle battery? Typical inverters cut off at 9.6 volts and my electronics will probably cut off at something like 5.5 volts. By that time, the control panel would have warned us to plug in the battery charger. Also, what if the cart will be plugged in while we are at our pit and run off battery otherwise?
Car batteries are designed to quickly discharge at over 200 amps to start the car and then be recharged by the alternator. They are typically only designed to be discharged at most 10% of there total capacity. Discharging the battery fully will shorten a car batteries life exponentially.
A deep cycle is designed to be discharged fully and recharged over and over but cannot supply as much amps as a car battery. Deep cycles are fully discharged when they reach around 11 volts (not 0v).
So how do you get rid of the H buildup? Can I just place vents. Also, I was going to monitor the battery thermally to make sure it doesn’t get too hot. Could that be good enough for preventing too much H buildup?
Thanks. That gets rid of some of my confusions. So what should I have the low voltage cutoff voltage to be?
Isn’t that dangerous? Could I mix it with oxygen and make water instead?
It’s not dangerous, since the quantities of hydrogen involved are very small.
That’s what you’re doing with a candle, using the oxygen in the air.