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MBITR Battery Box Conversion: Power The MBITR From An x90 Battery

NEW! There is now an NSN item that solves this problem! See in list below. NEW!

Special Forces almost universally use the MBITR (Multi Band Inter/Intra Team Radio) for team internal communications; conventional forces are also following their lead. Each MBITR comes with two rechargeable batteries that last ~12 hours, and one or two battery boxes that utilize twelve CR-123 batteries, providing power for ~9 hours. Teams almost never use the CR-123 boxes (many don't even bring them on deployment) because of the battery cost, battery load, and short runtimes.

Intensive interviews, discussions, and direct involvement on Special Operations missions has shown that even when in the mounted posture, commo losses due to battery issues are all too common. No general outcry has resulted from this as soldiers are generally unaware that there is another option. To address this issue, one can either purchase a full solution or fabricate a modification to the CR-123 battery box to connect the radio to an x90 battery (e.g. BA-5590). While larger than the standard battery, with even heavy usage a BA-5590 will run for at least for 96 continuous hours. Special Forces soldiers have reported doing an entire 10 day mission on one BA-5590 with energy to spare at the end. If they need to reduce load for a DA hit, they can easily switch to the smaller rechargeable battery.

The CR-123 battery box is a Class 9 item, making modification of it for other purposes a minor issue from an Army accountability standpoint. Detailed instructions on one method for modifying these boxes is provided below. An alternative is to purchase a completed solution as listed below, a few of which require providing your boxes to one of the following two vendors who will modify your boxes for you:

Commercial Purchase Options

Vendor	Part Number / NSN	Estimated Cost	Commentary
Preferably: use the supply system Alternate: www.electric-fuel.com	NSN: 5940-01-517-3990	~$270	This is your smart move if you can buy it. Not only is it an NSN item, but it allows you to connect to both x90 batteries (e.g. BA-5590) and the Zinc-Air batteries (e.g. BA-8180).
www.tacticaleng.com	SN-200	$150	These guys make nice stuff. Also a good source of pre-wired male and female x90 connectors.
www.mcdowellresearch.com	MRC-41	$???	This option has a more bulky waterproof box for the x90. Not the small/light option, but if you're going to go swimming, it's the solution to use.
www.amti.net	P-501	$???	This is a slightly different product: it allows input from 10-32VDC, thus you could hook it directly to a NATO Slave adapter or 24VDC source.
www.ABPCO.com	ABP-DCC-5590/ADPT-M	~$250	While I have not personally evaluated it, is probably the most technologically advanced of the "cut-down and convert" options. This conversion includes (allegedly) an accurate battery level transmitted to the radio and is short protected.
TSE Recon	N/A	~$160; you have to supply CR-123 box	TSE Recon is the original inventer of this solution and conversion. This is a conversion of a box that you supply. The only issue I have with TSE Recon's x90 based products is that they do not diode protect their x90 connectors. The chances for battery venting are admitted very very slim, but you have been duly warned.

Extra Note/Warning: Any modification or product that directly effects the operational capabilities of communications equipment must be taken very seriously. Poor wiring or manufacturing could result in communications loss: please consider this prior to undertaking this modification. If you do not feel capable of performing the steps adequately, you should not do so.

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Tools

Tool

Soldering Iron

Solder

Flux

Wire Stippers

X-Acto Knife

Voltmeter with Continuity (Bell) Function

Dremel tool with large cut-off disks, sanding drum, and knurled post attachements

Electric Drill with 15/64 and 5/64 Bits

Ruler

Straight Edge

Dental Tool (for fishing wires and scribing)

Pliers

Vice (Optional)

Clamps (Optional)

Canned or Pressurized Air (Optional)

Supplies

Part	Source	Part Number	Cost
5590 Connectors - Bare	www.baiaerosystems.com/connect.html	BAI-106G	$15/each; less in bulk
Diodes	www.digikey.com	sk32-7	$0.86/each; less in bulk
Wire	http://www.alphawire.com/pages/45.cfm	25062	?
Epoxy (gel is best)	Devcon	14240	?
CR-123 Battery Box	www2.thalescomminc.com	?	$185

Directions

For the purposes of these instructions, the "top" of the box is the part that connects to the radio.

1. Cut and Strip Power Cable

Cut a length of the 2 conductor power cable from three to four feet. Four feet will allow one to have the radio on the front of their body armor while locating the x90 battery in their backpack. From one end of the cable, strip off 2 inches of the cable jacket, then 1/2 inch of the positive lead wire and all two inches of the exposed ground wire. This is the end that will be inserted into the converted battery box.

2. - 4. Make/Wire the 5590 Connector To One Of The Cable Ends

Wire the 5590 connector only the non-battery box end of the 2 conductor cable. Follow steps 1-3 for wiring the 5590 connector here.

5. Remove Bottom and Plastic Insert

Unscrew the bottom cover and using pliers, pull out the translucent white central insert.

6. Measure, Scribe, and Cut Box Down

Scribe a line around the entire box at a height of ~1 inch from the top (the part that connects to the radio) of the box. Using the Dremel and large cut off disk, cut off the top of the box by cutting along the scribed line. After removing the top of the box, unscrew the two metal stand posts with pliers.

7. Cut And Prepare Bottom Cover

Using the cut-down box as a guide, scribe what will become the bottom cover on part of the remaining box material. Cut out this section using the Dremel and cut-off disk.

Using the drum sander on the Dremel, "clean up"/smooth around the edges of the underside of the new bottom cut out. This piece needs to lay flush with the bottom of the newly cut down battery box when glued with epoxy.

8. Drill and Prepare Positive Lead Connection

Use the electric drill and 5/64 bit to drill an angled hole through the center of the "third" positive battery contact grommet (see picture). It may help to completely read through Steps 8 and 10 prior to drilling this hole to understand why it's being drilled, so that you can adjust the drill angle and hole location accordingly. If you make a mistake, you can also use either of the other positive contacts, but this one works the best for a variety of reasons.

Dremel a small notch on the "outside" of the contact grommet with the gnurled dremel bit. This notch will aid in aligning the wire when wrapped around the grommet and increase the contact area.

Drill the hole through the center of the contact grommet at an angle; a wire will later be "fished" through this hole.	Dremel a small notch on the outside of the contact grommet to both increase electrical contact area and guide the fished wire.

9. Drill Cable Insertion Hole

Use the electric drill and 15/64 bit to drill and angled hole through the sidewall at the side opposite to the contact grommet hole drilled in Step 4.

10. Insert Cable And Wire Positive Lead Wire

Feed the stripped cable end through the angled cable insertion hole. Twist the end of the stripped positive lead wire (to help keep it together) and feed it down through the angled grommet hole.

Using the dental tool, fish the end back up, fold it over the grommet, and then using the dental tool push or "pack" the wire ends down into the grommet hole. Cut off any excess, stray ends that don't pack into the hole with wire cutters. The grommet itself is aluminum so you can't solder to it: the intent here is to tightly wrap the lead wire around this metal grommet and create tight contact. This tight contact will be reinforced with epoxy in a later step.

Dental tool used to fish out lead wire that is fed through the grommet hole	After wrapping the end of the lead wire back around, use the dental tool to pack the wire ends down into the drilled grommet hole. Cut off any excess ends with wire cutters.

11. Wrap Ground Wire And Confirm Wiring

Wrap the ground (negative) wire around several of the battery springs on the ground plate. Now is a good time to confirm your wiring: Connect the x90 connector to an x90 battery and using the voltmeter, test the voltage on the top of the battery box.

Close up of the wired box prior to soldering.	The two outer of the three "dots" or contacts are the positive contacts, while the center "dot" is the ground. The two metal side locks are also ground.

Note: the circuit board is responsible for some sort of voltage conditioning/regulation and thus the voltage using the center ground "dot" will be lower than when you test using the outer metal side locks. This also means you will not be able to "ring" the contact dots with the inside wiring for continuity checking; you can only check by applying a voltage from a battery and confirming voltage.

12. Solder Wires

Put some flux on both the ground wire connection points and the positive lead wire in the grommet and solder. While the solder won't stick to the aluminum positive grommet, it will reinforce the tightly packed lead wire prior to application of the epoxy.

13. Epoxy Contacts, Cable, and New Bottom

Using epoxy, put a generous 'gob' on top of the positive contact wire connection, the ground wire connections, and all around the cable at the intersection with the inside battery box wall (to ensure strain relief on the inside and water tight operation). Use epoxy around then entire bottom rim of the box, and then attach the new bottom cover and clamp until the epoxy cures.

14. Dremel-Finish Bottom

Using the Dremel with the sanding drum, remove excess epoxy around the glued seam and round the edges. Confirm wiring with the voltmeter again. Done.

Note: during operations one may want to tape the x90 connector on to the battery to prevent accidental disconnection. I have addressed that issue by inserting a velcro strap into the x90 connector prior to gluing: the strap wraps around the battery and keeps the connector securely attached, but many other methods are possible.