T-Pain Is On A Boat: [Electric Boats] Re: How do you measure how much battery life is left whlile you are out sailing?

Thursday, April 28, 2011

[Electric Boats] Re: How do you measure how much battery life is left whlile you are out sailing?

Interesting info Richard. As you pointed out there are many variables that may make such a chart inaccurate for a particular installation, but it got me to thinking...
It would be pretty simple to make your own chart for your own specific installation. It could be as simple as doing a timed run at a known amp draw and write down some voltage readings.
For instance, you could pre-calculate run times at some pre-selected normal cruise amperage to put you at 10, 20, 30, 40, 50, 60, 70, and 80% dod. Then go do the run and record the voltage at those dod points (times). The key is that it must be done at a known amperage to be repeatable.
Once you have your "cheat sheet", all you need to do is dial in your test amperage on the throttle and read the battery voltage. Refer to the chart to get approximate dod. By repeating the timed run occasionally and checking against your chart you would also get a good sense of the overall health of your system over time.
One possible issue I can see is that batteries will "recover" slightly after resting a while, which would render readings taken too quickly after throttle-up a bit optimistic. Might be best to run up to your "test amperage" and hold it while before taking the volt reading.
Does anyone see a problem with this technique or with my assumption that, for any given dod and amperage, there will be some repeatable voltage? I believe it to be fundamentally true but it seems almost too simple.
Jim

--- In electricboats@yahoogroups.com, Richard Mair <fullkeel2000@...> wrote:
>
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Battery Load Voltage vs. DOD
> Below are listed the 1 hour, 8 hour, 20 hour and 120 hour load voltages during the discharge
> cycle from full charge to 100% discharge to 1.75V/cell or 10.5V (6 cells) at 25Â°C (77Â°F).
> Â Â Â Â Â Â Â Â DOD (%)Â Â Â Â Â Â Â Â Â 1 hr. RateÂ Â Â Â Â Â 8 hr. RateÂ Â Â Â Â Â 20 hr. RateÂ Â Â Â Â 120 hr. Rate
> Â Â Â Â Â Â Â Â Â Â Â 10Â Â Â Â Â Â Â Â Â Â Â Â Â 12.23Â Â Â Â Â Â Â Â Â Â Â 12.60Â Â Â Â Â Â Â Â Â Â Â Â 12.65Â Â Â Â Â Â Â Â Â Â Â 12.69
> Â Â Â Â Â Â Â Â Â Â Â 20Â Â Â Â Â Â Â Â Â Â Â Â Â 12.16Â Â Â Â Â Â Â Â Â Â Â 12.51Â Â Â Â Â Â Â Â Â Â Â Â 12.55Â Â Â Â Â Â Â Â Â Â Â 12.58
> Â Â Â Â Â Â Â Â Â Â Â 30Â Â Â Â Â Â Â Â Â Â Â Â Â 12.07Â Â Â Â Â Â Â Â Â Â Â 12.39Â Â Â Â Â Â Â Â Â Â Â Â 12.42Â Â Â Â Â Â Â Â Â Â Â 12.45
> Â Â Â Â Â Â Â Â Â Â Â 40Â Â Â Â Â Â Â Â Â Â Â Â Â 11.96Â Â Â Â Â Â Â Â Â Â Â 12.25Â Â Â Â Â Â Â Â Â Â Â Â 12.28Â Â Â Â Â Â Â Â Â Â Â 12.32
> Â Â Â Â Â Â Â Â Â Â Â 50Â Â Â Â Â Â Â Â Â Â Â Â Â 11.83Â Â Â Â Â Â Â Â Â Â Â 12.11Â Â Â Â Â Â Â Â Â Â Â Â 12.15Â Â Â Â Â Â Â Â Â Â Â 12.18
> Â Â Â Â Â Â Â Â Â Â Â 60Â Â Â Â Â Â Â Â Â Â Â Â Â 11.70Â Â Â Â Â Â Â Â Â Â Â 11.98Â Â Â Â Â Â Â Â Â Â Â Â 12.02Â Â Â Â Â Â Â Â Â Â Â 12.05
> Â Â Â Â Â Â Â Â Â Â Â 70Â Â Â Â Â Â Â Â Â Â Â Â Â 11.55Â Â Â Â Â Â Â Â Â Â Â 11.79Â Â Â Â Â Â Â Â Â Â Â Â 11.83Â Â Â Â Â Â Â Â Â Â Â 11.88
> Â Â Â Â Â Â Â Â Â Â Â 80Â Â Â Â Â Â Â Â Â Â Â Â Â 11.38Â Â Â Â Â Â Â Â Â Â Â 11.59Â Â Â Â Â Â Â Â Â Â Â Â 11.61Â Â Â Â Â Â Â Â Â Â Â 11.65
> Â Â Â Â Â Â Â Â Â Â Â 90Â Â Â Â Â Â Â Â Â Â Â Â Â 11.15Â Â Â Â Â Â Â Â Â Â Â 11.32Â Â Â Â Â Â Â Â Â Â Â Â 11.34Â Â Â Â Â Â Â Â Â Â Â 11.40
> Â Â Â Â Â Â Â Â Â Â Â 100Â Â Â Â Â Â Â Â Â Â Â Â 10.50Â Â Â Â Â Â Â Â Â Â Â 10.50Â Â Â Â Â Â Â Â Â Â Â Â 10.50Â Â Â Â Â Â Â Â Â Â Â 10.50
> Please note that these voltages are averages and will vary slightly from battery to battery even
> of the same rating. They are, however, a good indicator of state of charge and can be used
> when setting low voltage alarms or disconnects for a Concorde AGM battery. Other battery
> types or manufacturers voltage vs. DOD may be substantially different. The data is for newer
> batteries with relatively few cycles. An older battery will measure a lower voltage for a given
> DOD.
>
>
> I got this from lifeline batteriesÂ website..Should be close for AGMs
> Richard
>
>
> ________________________________
> From: Arby bernt <arbybernt@...>
> To: electricboats@yahoogroups.com
> Sent: Thursday, April 28, 2011 5:31:15 PM
> Subject: Re: [Electric Boats] Re: How do you measure how much battery life is left whlile you are out sailing?
>
>
> Â
>
> Hi Brett,
> You can measure the realtime capacity of a wet battery by measuring the specific gravity of the electrolyte. Loaded or resting will not matter. AGM's are a bit tougher. Harbor Freight offers an electronic tester that uses high frequency loading to measure the battery response. I don't know if it will measure realtime capacity under load, but it will show the capacity at rest.
>
> Let the EB list know how it works out.
>
> Be Well,
> Arby
>
>
> --- In electricboats@yahoogroups.com, "m8trixman" <pb@> wrote:
> >>
> >> 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
> >>
> >
> >
>