I’m working on a battery powered cellular mobility box for a client. They’ve asked if it was possible to incorporate a small battery UPS into the box to prevent a cellular disconnect when the battery runs out. It doesn’t need too much power, 12v at roughly 50 watts. There are a few UPS pcb’s on Amazon but I’m not sure I have too much faith in those.

Any recommendations?

 

First off, what is a "cellular mobility box" ?

Battery-Powered-Cell-Phone-"Chargers" are as common as weeds,
what problem are You trying to solve that is not addressed by these very common devices ?
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It’s a Pelican case with a Peplink cellular router with four bonded cellular radios for film production. The box will run on AC, and cinema gold mount batteries. When the battery gets low and need to be changed, assuming no AC power avail, having a small short term UPS will prevent the unit from going offline. The Peplink devices can take 10-15mins to power up, get connected and establish the bonded connection.

so I’m looking for a PCB or small unit that will provide 5-10mins of stable power while batteries are being switched out.

 

I suggest a separate battery pack that can deliver the required power for 30 minutes, although the present request seems to be 15 minutes. That provides a bit of safety margin. And just an "OR" type of change over because it is more reliable.

 

I suggest a separate battery pack that can deliver the required power for 30 minutes, although the present request seems to be 15 minutes. That provides a bit of safety margin. And just an "OR" type of change over because it is more reliable.

I don’t disagree, the issue is, I can’t find a PCB anywhere that will work for my needs. Seems all the systems are designed for rPi’s or modems which do not draw too much current.

 

A PCB is not the priority here, and may not be necessary at all.
The degree of portability, and location circumstances will dictate many decisions regarding this problem,
as well as the actual running Current requirements.

Do You carry a huge pile of equipment into an indoor location for Video-Recording ?
If this is the Case, I would suggest one more piece of equipment strapped to a small Hand-Truck.

Go to a NAPA-Auto-Parts-Store,
Purchase an Optima "Blue-Top" Deep-Discharge AGM Battery, ( the required size is yet to be determined ),
Also purchase an "Automatic-Battery-Maintainer",
( the personnel in a NAPA-Store are generally well qualified to help with your selection ),
Also purchase a 120-Volt Power-Converter, ( the power-capacity is yet to be determined ),

Strap all this stuff to a "light-duty" Hand-Truck with nylon-straps or other creative mounting methods.
The Optima-Battery is completely sealed and can not leak,
it can even be mounted up-side-down.
The Terminals on top of the Battery must be protected against
accidental contact with any other Metal parts which may fall against them and cause a Short-Circuit.

Now You have AC-Power wherever You can wheel your Hand-Truck.
It can be used for Charging Batteries, and also, running equipment while Batteries are being swapped.

The Hand-Truck may also serve other uses at the same time.
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I own and use two of the smaller inverters that run on 12 volts. I can't vouch for the purity of their power, but they do work for power tools within their ratings.
Each one draws about ten amps when powering a single 100 watt incandescent lamp, when the supply voltage is 12.0 volts. So the battery drain versus time needs to be considered. As the voltage drops the current draw increases because they do seem to be regulated to supply a constant voltage.

My impression was that the TS equipment described could operate from twelve volt batteries directly. THAT would be a much better situation and vastly more efficient, if all of the equipment could operate directly from the battery. Operating from 120 volts AC means first converting battery power to AC and then powering five separate power supplies to provide low voltage DC for the individual components. So the efficiency would be possibly as good as 90% of 90%, if all of the conversions were 90% efficient.

 

Hello, how did your last project go? Did they actually put the repeater on the air? Was if confirmed as compliant with FCC regulations?

About this, two things.

1. I am assuming that you are using 14.8V batteries. How many? How are you getting the voltages you need to run the router, etc.? Would it be possible to have the grip use a procedure that involved plugging the box into an inverter before swapping batteries?

The logic of the last is that there is no functional difference between a 30 minutes remaining alarm on the main battery and letting the main batteries run out and getting a 30 minute backup alarm. So, as long as you know that batteries must be changed, a small, external deep cycle marine battery and inverter in a box would cover the time for the change. It’s just a checklist item to be sure you’ve attached the inverter before swapping.

Alternatively, since the current requirements aren’t likely to be very high, an inverter built in to the box with a 12V input for an external source would reduce the weight compared to including the battery as well. All of this is predicated on the idea that you can, already, in fact hot swap AC for battery power. If not, then it’s not relevant.

One thing to consider is that the cinema batteries’ 14.8V max voltage is higher than the 13.8V max of an SLA (Sealed Lead Acid) battery, so it may be possible to connect an SLA battery to the output of the regulator that is powering the router, etc., and let it float (I am assuming 12V out from the regulator). If the input voltage to the regulator dropped, the SLA would being to discharge naturally. This requires no special circuitry but might need a diode for steering so the battery can’t try to power the regulator.

2. Have you considered not tying up stupidly expensive cinema batteries and instead using, for example, Makita 18V tool batteries? This would seem to have a lot of advantages. While it does require a separate set of batteries for the mobility box, the cost savings are enormous and you won‘t have your Anton Bauers mounted to the box when your cameras or lighting are showing red for battery state.

A Makita 90wH battery, the real thing, will run you less than 50 bucks. This means for the you are paying about a $0.50/Wh where with cinema batteries you are paying something like $4.00/Wh without any real advantage in terms of powering the particular gear.

Perfectly good aftermarket battery options can bring the Makita cost down to as low as $0.30/Wh. You can also buy Makita batteries almost anywhere in a pinch. Also, chargers—well, you know what you would pay for an Anton Bauer charger, the Makita chargers are a quarter or less.

 

Hello, how did your last project go? Did they actually put the repeater on the air? Was if confirmed as compliant with FCC regulations?

About this, two things.

1. I am assuming that you are using 14.8V batteries. How many? How are you getting the voltages you need to run the router, etc.? Would it be possible to have the grip use a procedure that involved plugging the box into an inverter before swapping batteries?

The logic of the last is that there is no functional difference between a 30 minutes remaining alarm on the main battery and letting the main batteries run out and getting a 30 minute backup alarm. So, as long as you know that batteries must be changed, a small, external deep cycle marine battery and inverter in a box would cover the time for the change. It’s just a checklist item to be sure you’ve attached the inverter before swapping.

Alternatively, since the current requirements aren’t likely to be very high, an inverter built in to the box with a 12V input for an external source would reduce the weight compared to including the battery as well. All of this is predicated on the idea that you can, already, in fact hot swap AC for battery power. If not, then it’s not relevant.

One thing to consider is that the cinema batteries’ 14.8V max voltage is higher than the 13.8V max of an SLA (Sealed Lead Acid) battery, so it may be possible to connect an SLA battery to the output of the regulator that is powering the router, etc., and let it float (I am assuming 12V out from the regulator). If the input voltage to the regulator dropped, the SLA would being to discharge naturally. This requires no special circuitry but might need a diode for steering so the battery can’t try to power the regulator.

2. Have you considered not tying up stupidly expensive cinema batteries and instead using, for example, Makita 18V tool batteries? This would seem to have a lot of advantages. While it does require a separate set of batteries for the mobility box, the cost savings are enormous and you won‘t have your Anton Bauers mounted to the box when your cameras or lighting are showing red for battery state.

A Makita 90wH battery, the real thing, will run you less than 50 bucks. This means for the you are paying about a $0.50/Wh where with cinema batteries you are paying something like $4.00/Wh without any real advantage in terms of powering the particular gear.

Perfectly good aftermarket battery options can bring the Makita cost down to as low as $0.30/Wh. You can also buy Makita batteries almost anywhere in a pinch. Also, chargers—well, you know what you would pay for an Anton Bauer charger, the Makita chargers are a quarter or less.

the repeater became a fiasco, the owners of the flight company had a massive fight, no one would return any of my emails or calls. So in the end it never got built, and I still have the repeater sitting in my storage unit.

As for this box, I’ve built over a dozen of these and this is the first time anyone has requested a UPS style setup. I think I’m just going to convince them to add an additional battery mount instead, that would be the easiest solution.

As for some of the questions, the reason we use cinema batteries is two fold, one the client owns a bunch of them, and second those batteries are always available on motion sets. If I was building for someone in a different industry I would definitely recommend using power tool batteries.

These units will travel all over the place so portability is key. The G&E guys often don’t have power available immediately and often times they kill power when their lights are no longer needed.

 

the repeater became a fiasco, the owners of the flight company had a massive fight, no one would return any of my emails or calls. So in the end it never got built, and I still have the repeater sitting in my storage unit.

As for this box, I’ve built over a dozen of these and this is the first time anyone has requested a UPS style setup. I think I’m just going to convince them to add an additional battery mount instead, that would be the easiest solution.

As for some of the questions, the reason we use cinema batteries is two fold, one the client owns a bunch of them, and second those batteries are always available on motion sets. If I was building for someone in a different industry I would definitely recommend using power tool batteries.

These units will travel all over the place so portability is key. The G&E guys often don’t have power available immediately and often times they kill power when their lights are no longer needed.

Sorry to hear about your bad client. I can certainly sympathize.

I understand about the “we have these batteries” but, my goodness the premium you pay for them, it‘s absurd!

What is the run time of the mobility box? Is there more than one plate for batteries already? Are they paralleled?

 

With a 98wH battery the unit will get around 3hrs. The Peplink itself has a wide voltage range, 12-56v (48v+ will enable POE). If I do two battery mounts, I’d connect them in series to prevent any voltage spikes.

 

Maybe a pair of Schottky diodes would work as a battery isolator. Like this:
https://forum.contextualelectronics.com/t/what-does-the-schottky-diode-do-in-this-schematic/544/4