Brett-
Traditionally, this has been done by monitoring the amp-hours removed from the battery pack after a full charge and subtracting that from the expected capacity of the batteries. The approach hasn’t really changed ---electric cars of a hundred years ago started using DC amp-hour meters made by Sangamo (I have one on my 1920 Milburn Electric car) to mechanically accumulate and display the equivalent amount of amp-hours removed from a pack. And those meters use the same technology that has been in use now 100 years later to monitor all of our home and business power usage. But while those devices are very accurate, they are bulky and heavy. So for today’s electric vehicles, modern electronics are used in conjunction with a current shunt in attempting to accurately accumulate the charge/discharge amp-hours. There are many manufacturers and options these days including:
· PakTraker: http://www.paktrakr.com/
· Emeter à Link10 à E-xpert pro: http://www.tbs-electronics.nl/products_expertpro_features.htm
· Evision by MetricMind: http://www.metricmind.com/evision.htm
· Others
A good number of folks on this list use the first 2 options above. In the EV car community, a growing number are using the 3rd option above, which should be considered a high-end, high performance option. Considerations: Cost (Paktrakr’s the cheapest), robustness (Emeter and its descendents at risk of blowing front end current monitoring electronics---need to be careful---I have used a Link10 for over 7yrs now), ability to see (Evision is tops), voltage range (Evision most flexible), ability to correct for Peukert and other effects, programmability, interface with computers/accessories, power consumption, size, etc.
If you want to be really cheap, you have options:
· Monitor voltage alone
· Monitor current and manually take readings over time to create your own mechanical amp-hour accumulation record.
You’ll likely quickly decide that the electronic devices are the way to go.
Best-
-MT
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of m8trixman
Sent: Wednesday, April 27, 2011 8:18 PM
To: electricboats@yahoogroups.com
Subject: [Electric Boats] How do you measure how much battery life is left whlile you are out sailing?
What is the best way to measure what percent of battery life is left while you are out motoring?
Thanks for taking the time to chime in on this question...
Brett
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