Re: Driver station power
 

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.

Re: Driver station power
 

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.

Re: Driver station power
 

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.

Re: Driver station power
 

I agree with that. Do you by chance know how to get rid of this H?

Re: Driver station power
 

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?

Re: Driver station power
 

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).

Re: Driver station power
 

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?

Re: Driver station power
 

Thanks. That gets rid of some of my confusions. So what should I have the low voltage cutoff voltage to be?

Re: Driver station power
 

Isn't that dangerous? Could I mix it with oxygen and make water instead?

Re: Driver station power
 

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.

Re: Driver station power
 

Unless your enclosure is hermetically sealed you should be fine.

Re: Driver station power
 

Time to end the speculation. Part of the battery chemistry is sulpheric acid which is a combination of sulpher and water (H2O). When current is passed through water the eletrical bond between H and O become overcome and the molecule breaks into H2 and O. In normal cases, what molecule break naturally occurs during charge and discharge recombines as water without ever leaving the battery. However, there is always the possibility that hydrogen is vented to the atmosphere in and around the battery along with oxygen. That combination is explosive if left to buildup and is exposed to any ignition source like a spark or hot soldering iron. Remember the Hindenburg?
Deep cycle batteries are nearly identical in design to normal batteries except for a few design differences. The deep cycle has different plate design to withstand high current demands for longer periods of time and there is a deeper reservoir beneath the plates. During normal charge and discharge cycles in lead/acid batteries, some particulate forms in the solution and much of it drops to the bottom of the battery. Over the life of the battery, this particulate builds up and eventually shorts out the bottom of the plate area. This not only shorts the charge stored in the cell it also shunts charge current preventing the chemical reaction to be reversed.
As to capacity, there is no blanket statement to be made here. The amp hour specification of our robot batteries are specified to about 1.7 volts/cell or about 10 volts, depending on discharge current. However, during normal use, the voltage drop across the internal resistance of the battery can actually appear to be much lower on a fully charged battery.
We have all become complacent in handling robot batteries since they can be used and charged in any orientation. (I still do not recommend charging upside down.) Car batteries and deep cycle batteries, in general, should only be used in one orientation and never allowed to tip or turn over to prevent spills.
Now to the other dangers. Robot batteries are capable of 600 amps when fully charged. That is capable of welding metals when used improperly or not fully insulated. Car batteries are capable of at least three times that current and deep cycle batteries even beyond that. The batteries you are talking about are also much heavier than robot batteries. One of my coworkers dropped a small car battery on his foot and broke his toe.
So as you can see there are a number of issues that need to be addressed before your ideas and design is safe for all participants.

Re: Driver station power
 

Thanks, Al. That reduces quite a bit of confusion. However, when looking at car batteries, the maximum discharge I could find was 700
Amps. Also, I thought robot batteries support a maximum of 250 Amps.

Re: Driver station power
 

You have to read the spec sheet. A typical replacement battery for my car is capable of over 900 cranking amps and is rated for 44 Amp/Hr. with a reserve capacity of 100 minutes at 25 amps. Pulse currents of 50% higher is not uncommon with short circuit currents nearly triple the cranking current. So max current is nearly 3000 amps compared with our 600 amps max draw. For both batteries, this current will produce a voltage drop across the internal resistance which prevents the battery from supplying 12 volts at that load. Delivering short circuit current to four feet of #10 wire should a fault occur, will produce nearly 36000 watts. The result is burning wire, and very hot, dripping, melted insulation. To use a battery of this type requires some good circuit protection in the form of fuses and high current switching. I have seen high currents fuse the contacts of a switch preventing it from opening the current flow.

Re: Driver station power
 

Cool. I didn't know that 3000 amps could be drawn from a typical battery. I would think that the battery would melt, the terminals might evaporate and there would be a big explosion because of all the hydrogen gas buildup. I also think that the insulation must have evaporated by then