Flat? battery

[mick]

The other day, while sailing, I had been running my new Garmin Gpsmap 555 chartplotter for about three hours or so when the low voltage alarm went off. As it's set at 11.2 volts and the battery was recently charged, I was a bit surprised. I used this battery shortly after this to start the engine, which fired instantly. Surely if the voltage was 11.2 the battery should have been flat. I contacted Garmin and the technical person I talked to was surprised to hear what had happened, insisting that the voltage measurement should be accurate. He said the maximum draw should effectively be in the region of 750 milliamps. Any suggestions about what might be happening here?

 

[smeaks]

is the power lead/connection giving a series voltage drop so the unit is seeing less than that of the battery cells?

 

[halcyon]

You need to start with your voltmeter.

Check the voltage at the battery, check the voltage at the chartplotter, you could just have a bad joint.

Brian

 

[savageseadog]

[ QUOTE ]
is the power lead/connection giving a series voltage drop so the unit is seeing less than that of the battery cells?

[/ QUOTE ] It's very common for wiring to be undersized and/or corroded. This will be especially apparent when there is a load like nav lights, instruments, bain lights etc.The way to check is put the negative of a digital meter directly to the battery negative terminal, using a length of extra wire as necessary. Connect to the positive battery terminal note the reading and and follow the wiring through to the Garmin. More than likely you will find the voltage at the switch panel to be a fair bit less than at the battery. Not forgetting the negative side of things. Measure the voltage on the negative side of your Garmin, you will find a small or very small voltage there. You will need to renew and/or size up the wiring terminals etc.

 

[davidej]

We had a similat sort of problem with a Garmin C3010 and fitted a digital voltmeter straight to the battery (about £12 on ebay - claimed 2% accuracy). This always registers 0.4-0.5V more than the chartplotter despite more than adequate cables mainly soldered.

We gave up worrying about the frequent alarms and rely on the voltmeter.

 

[mick]

Thanks, all.

 

[Refueler]

I convinced my reluctant wallet to open to the tune of 21 quid. I bought a battery meter that can give reading of 2 batterys ... with a 1 - off - 2 flick switch. It's analogue and sits there waiting for me to switch ...
It may not be a Battery monitor or fancy - but it's been a godsend. Couple of weeks ago - as usual when I go on-board - I flick the switch to check batterys .. batt 1 didn't show at all ... Oh Oh !! Batt 2 was over 12V and good.
Now without that meter I would never have known till needing Batt 1 .. turned out to be a dody connection ... 5 mins later Batt 1 shows 12V+

Can you imagine if I had started engine on Batt 2 as I do, then flipped to Batt 1 to charge ? BHAM - that's my alternator diodes shot !!

Yep - good bit of kit and simple.

For those who are scrooge as I - it can also be done with an old multi-meter ... just wire it up through a 1-off-2 switch and mount .. leaving meter on DC Volts .... I was going to uise an old small analogue meter I have laying around. Then I saw above ready made job.