Running sbRIO off standard batteries

[falkpl]

I am looking at sbRIO fo a possible portable device, requested that the device takes standard batteries (AA, C or D cell).  Is this possible, how long would the system run for (assuming some small set of external devices)?

[Ben]

aside from the rio spec I believe that depends on the battery spec and quality of charge. batteries generally are rated in Amp-Hours.

I think you can figure the rest out.

Ben

[Spex]

Hi Paul,

Depending on the Single-Board RIO, you will need to stack cells to acheive the required input voltage range (9-30V or 19-30V).  Keep in mind the power ratings in the user manual are theoretical maximum (worst case) calculations and your power consumption will be lower than the values published, as demonstrated in this knowledge base.  Ideally you would benchmark your own application to determine the max and stead-state power draw, but I understand you are in feasibility study mode now, so theoretical is the best start.

I'll throw down some chicken scratch math...  

Assuming sbRIO-9605 with 9-30V input voltage range has actual "measured" power consumption similar to cRIO-9075 documented on link above (sbRIO-9605 and cRIO-9075 share the same internal architecture).

cRIO-9075 documented at 3.5W measured, add ~30% for good measure => 4.5W @ 24V

Assuming D batteries - rated from 2 Amp-Hours to 18 Amp-Hours depending on composition (thanks wikipedia)

Current draw to sbRIO would be ~.375 Amps at 12V (8-10 Cells depending on cell chemistry) - 5 to 48 hour battery life expected

Current draw by sbRIO would be ~.5 Amps at 9V (6-7 Cells depending on cell chemistry) - 4 to 36 hour battery life expected

Operating time could be increased by added more batteries in parallel, but that is already a lot of proposed batteries just to get to the operating input voltage... so what about 9V batteries?

Internal to a 9V battery is essentially 6 AAAA cells at 1.5V wired in series to get to 9V.  Therefore you would expect an Amp Hour rating simiar to a AAAA battery.  At .12 to 1.2 Amp Hours, a 9 Volt battery may power the sbRIO-9605 for 15 minutes to 2.4 hours.  Again, 9V batteries could be placed in parallel to boost operating time.

Another caveat to consider is the voltage sag that occurs with a battery as it discharges.  You would need to ensure that your battery stack doesn't sag below the 9V input operating range through out any transient power surges in your system or risk a brown out condition.  The change in output voltage from each battery will vary according to the battery chemistry as well.  

I honestly haven't tried to power a Single-Board RIO or CompactRIO from standard batteries.  The products certainly were not designed for the level of power consumption and power management that would typically be involved in a hand-held battery powered application.

If you give this a shot (or don't), I'd like to know more about your application and what run times you would like to see from NI embedded products in portable applications.

Cheers,

[johnsold]

Paul,

Based on the data Spex provided, I would suggest that a better alternative might be sealed lead-acid batteries. Two twelve volt batteries and a small charger should keep things running for days.  Use of two batteries would allow one to be charging while the other is running the system.  Add a couple of diodes and you could have a hot-swap system, allowing exchange of batteries without shutting down.

The batteries are rectangular with quick connect or screw terminals. They would not cost much more than a batch of small battereis and you do not need to wire up the battery holders.

Lynn

[falkpl]

Thanks for all the information.  I will see if the client is open to less standard batteries and explore the choices.

[falkpl]

One other option is to possibly use fewer batteries (say 4-6 D Cells) and use a DC-DC Bost to regulate at 12V.  I am looking at all options but am supprised this has not been done before. 

[johnsold]

Paul,

Since the sbRIO seems to have a fairly wide input voltage range, it probably has a DC-DC converter internally and a regulated input is overkill.  Plus you get the inefficiency of another conversion, making the required battery capacity higher.

Lynn

[falkpl]

Does this leave me at 12V worth of D-cells to make sure I have enough voltage 12V and drains down to 9V I was hoping to use less batteries since they make the device bigger.  The 12000mAH is plenty but the voltage is a problem, I was hoping to beable to use 6 batteries and boost the voltage up as needed.

[johnsold]

Paul,

That might be a reasonable tradeoff.  I looked up a DC-DC converter, nominal 5 V input and 12 V output at 6 W. (TDK-Lambda CC6-0512SF-E, $17.52 from Digi-Key). Actual input range is 4.5 to 9.0 V. You could use 4 or 5 cells with this device.  At the current estimated by Spex and the minimum efficiency specified for the converter, you would get about 12+ hours out of 18 A-hr D-cells.

Digi-Key has 19 A-hr primary D-cells for ~$17 each, not in stock, minimum order = 100. The largest rechargeable D-cell they list has about half the capacity and is priced at > $33 each.

A 12 V, 12 A-hr sealed lead-acid battery would last > 20 hours, is 6"x2.6"x4.6" and costs ~$40.

Unless your customer has access to cheap D-cells, I think I would try to convince them that the economics favor the 12 battery.

Lynn

[SnowMule]

Design requirements should outline the runtime of the system on a battery with a full charge.  From that, spec the batteries.... comes down to energy density.  Batteries with higher ED = higher cost, smaller size.  Cheaper SLA/AGM batteries will give you the performance and price point at the expense of physical size and weight.  They're also easier to charge than LiIon/LiPo cells, further reducing manufacturing costs. 

Why the choice of "standard" cells, vs. something with higher ED that can be swapped out (think laptop or two-way radio batteries)?

If you need a lot of power for a long period of time, there's no getting around having a big battery.