Here's the article referred to.
IS IT CHARGING?
For many of us at the smaller end of the sailing scale, boat electrics can be a rather basic but are no less important for that. A single 1 2v battery re-charged by the outboard is a pretty common arrangement and those of you who have a similar set-up will know that outboards don’t give much charge and we’d all rather sail than motor anyway. It’s therefore reassuring to know that the engine is charging properly when you do have it running.
The demand-side of the battery seems to get ever more, well, demanding. On Gentoc (235/22) we run the usual lights, VHF and echo-sounder plus a Garmin 176 GPS plotter but have also added a small Waeco portable fridge beneath the companionway steps. This luxury—and it really does transform cruising to have a cold beer and safe food on a hot day, so it’s become a highly-valued item aboard—is a proper compressor fridge, so it uses much less power than cheaper thermoelectric coolboxes, but still takes over 3 Amps when it’s running (which it does for about 10 minutes in the hour).
Unfortunately, I’ve never been very confident that our outboard has been delivering charge and, whilst it does a great job of keeping the battery topped up whilst the boat is unattended, the small solar panel on the coachroof only adds about half an amp at most. So I’ve spent too much time prodding various terminals with a multi-meter, trying to work out if the battery is happy and if the engine is adding any amps at all. When cruising, we have come to rely on a battery charger plugged into pontoon power every couple of days, which rather limits our scope to find wild anchorages. I bought a Cetec digital charger, by the way, and it’s excellent—much better for the battery than a car charger.
Proper battery monitoring systems that really show what’s going on in the battery—voltage, current and capacity—all seem to be prohibitively expensive but when I saw adverts for a new NASA device, the BM- 1, at £99 I decided to fit one. The instructions were very clear so the installation wasn’t too stressful—the worst bit was deciding where to cut a hole in shiny GRP to fit the display. The wiring bit is easy; you remove the all wires from the negative terminal of the battery and replace them with a 20cm long thick wire connected to one side of a ‘shunt’. This shunt is an insulated block which you bolt onto a bulkhead near the battery and has two large brass terminals joined by a strip of metal. The wires that you removed from the negative battery terminal go onto the second terminal of the shunt and then small voltage and current measuring wires connect from the display unit to the positive battery terminal and the two shunt terminals. The kit comes with a 3m long cable allowing you to mount the display unit wherever suits you best (it is spray-proof so it can be in the cockpit) but I put it at the end of the starboard berth, close to the battery, to avoid a tricky wiring run.
Once connected, there are a few button-pushing combinations to go through to tell the system the size of the battery (or bank of batteries) and then it ‘learns’ the characteristics of the battery over the first half hour of running a load such as the cabin lights. There are three options for the display that you can select: the first shows volts and amps (either leaving the battery or charging it); the second shows percentage capacity charged together with an estimate of either the time the battery will last at the current load, or how long it’ll take to charge at the present charging current; the third calculates the net charge or discharge in Ampere-hours since you last pressed a reset button.
Having finished the installation with not too many swear words, I was delighted to see the solar panel contributing 0.SA on a sunny March day but was less delighted when I fired up the outboard to see no charge at all registering. This at least confirmed my suspicions and so I systematically went through all the connections and fuses between engine and battery to find that the chromed-brass, two-pin deckplug would only make connection if wiggled in a certain way (I’ve now replaced it with a much better unit) and the in-line ‘bullet’ 8A fuse was definitely only playing ball when it felt like it. These things sorted, the readout shows 2A charging at tickover and up to 4.5A at fast cruising speed —not a huge charge if you are used to a diesel engine delivering 40A, but at least I know it’s working!
So, so far, I’m pleased with the NASA battery monitor, the real test of its usefulness will be after our two-week cruise to Falmouth. I’ll report back....
Graham Keating, Gentoo, Parker 235/22
Regards
Don Harvey
Web Master
Parker 325 'Calypso'