Camper Trailers Tech Tips

NASA BM1 Compact battery monitor install





nasa bm1 compact
battery monitor


NASA BM1 Compact battery monitor

I had been looking around for some time to install a suitable battery monitor to let me know the 'state of charge' of the deep cycle battery in our Cub Camper Trailer, more than the information a voltmeter gives. It was not an easy process as there were a few problems to work around.....

* Most battery monitors are not water proof or UV stable
* Something decent was always going to cost some dollars
* I needed a unit that wasn't bulky
* It had to be seen when the camper was packed & stored in the garage
* I didn't like the idea of cutting into the original panels
* How to fit cheaply & easy without major changes

I needed a quality monitor that would last the test of time. Some of the cheaper units had bad reviews or no information about them, like some that were advertised on Ebay. The NASA battery monitor range had a good name & was recommended to me by members of the CamperTrailers Group who use them. They are built for a marine environment so no doubt would perform well in the dusty & road vibration conditions subjected to the camper trailer. 

I ended up purchasing a NASA BM1 Compact battery monitor for $225 delivered with one year warranty & measures only 124mm x 62mm x 23mm with a screen size of 50mm x 60mm. Along with the monitor comes a five metre length of cable prefitted with terminals, a fuse & a 100amp shunt.

Now where to mount the monitor. After careful consideration I found the perfect location to be on the side of the pantry draw. Here I could slide the draw out whether camping or at home for a quick look as to the battery state of charge.

parts required

* two metres of 16mm steel core, PVC coated conduit & end fittings
* Aluminium angle for end fitting mounts
* Cable ties
* Cable tie mounts
* Heat shrink of different diameters
* Pop rivets
* Two screws for mounting bracket


* cordless drill, 4.8mm cobalt tipped drill bit & a phillips head driver bit
* Steel cutting compound - used when drilling stainless steel, stops the heat build up
* Pop riveter
* Shifter & 10mm spanner
* Small phillips head screw driver
* Crimping tool
* Heat gun
* Scissors

in position

This photo shows the pantry fully opened with the NASA BM1 Compact battery monitor mounted to the rear side giving it more protection.

In this position there is around three metres of cable length from the monitor to the battery.

I made up some end fitting brackets from aluminium angle & pop riveted into place using cable tie brackets to mount the conduit. 




This photo shows the pantry open at 300mm making the monitor easy to at any time especially when sitting down under the awning when camping.

Photo taken from inside the camper showing the pantry in its closed position & before I put the two cable ties in place where the cable goes right at the top of the conduit loop.
Showing the pantry open about ninety percent. The conduit just loops back & stores next to the pantry when packed away. Only need to keep about 100mm clear space next to the pantry.

how it works

The  NASA BM1 Compact battery monitor continuously monitors voltage, current (charge or discharge), number of amp/hours (charge or discharge), the batteries state of charge and the time to charge or discharge via the 100amp shunt on the negative side of the battery. If you do not want to read the figures, there is a battery indicator gauge on the right hand side of the screen. The information the monitor provides leads to more efficient use of the battery resulting in a longer battery life.

The BM1 uses 1.5 mA which is about 1 amp hour a month.

Showing the battery voltage, the discharge in amps & graph up the right hand side of the battery state of charge.
Showing the battery state of charge percentage & hours remaining.


For more information please check the NASA Marine website


thanks to Peter Higgs for this article



april 2014