good and cheap digital Votage display?

witzgall · 10-06-2008, 15:31

HI all;

We have idiot lights on our boat showing battery condition. I would like to install a simple digital voltmeter. I know I can buy a Blue Sea or another marine product, but has anyone used a inexpensive meter with good results? If so, what was it?

Chris

**GordMay** · 11-06-2008, 02:45

Voltmeters, especially cheap ones, really don’t tell you very much about battery condition.

Quoting Rick, who literally wrote the book*
on battery condition monitoring:

Quote:

Originally Posted by Rick

First, the state of charge of any lead-acid battery cannot accurately be determined by voltage. More importantly, the state of capacity can in no way be determined by voltage readings...

Rick won't blow his own horn, so here's a short biography:
Rick is of President ACUTRA, a team of net-worked engineers, designers, subcontractors, and supply sources, who manufacture and markets niche specific products (ie: LGC-LX automatic generator controller/remote).

Rick previously owned and operated Cruising Equipment Company in Seattle Wa. The company was founded in 1984 and was sold to Valley Forge Corp. in 1993. Rick continued to serve as president until 1999. Cruising was a market leader in battery state-of-charge instrumentation, charge regulation, inverter/charger remote controls, load management, and small power systems integration. He led the development of more than 20 product platforms. His team acquired six patents and many of their products continue to dominate their niche. Valley Forge was sold in 1999 and Rick left the company to pursue further education and consulting career. Cruising eventually was acquired by Xantrex of Burnaby BC.

His most recent project was the development of a line of eight digital meters for AC and DC parameters for Blue Sea Systems of Bellingham, Wa. These meters are very cost competitive, accurate, and easy to install. They are finding application in Marine and RV as well as industrial markets.

In June 2001 Rick added an MBA from the University of Washington to his Bachelors in Electrical Engineering from the University of Missouri.

Rick holds several important patents, for instrumentation & control products.

See also:
http://www.cruisersforum.com/forums/...atts-9165.html
And:
http://www.cruisersforum.com/forums/...stem-9147.html
And:
http://www.cruisersforum.com/forums/...ance-1442.html

witzgall · 11-06-2008, 06:37

Right, I understand that. But they would tell us more than three idiot lights, no?

Chris

**Pblais** · 11-06-2008, 06:38

Chris,

The links posted by Gord are some good ones on this subject. We have a large amount on this topic posted already. Battery monitoring is the key phrase above.

What you want is something like a fuel gage for your batteries and that is exactly what battery monitoring is. A volt meter measures only volts and a battery monitor measures power. Power is measured in Volts X Amps X hours. Just knowing the volts is not even close to the correct answer. While a voltage of 10 volts means the bank is toast you don't get clarity from just knowing the voltage. The idiot light can do that for you just as well.

Battery monitoing goes so far beyond that by showing exactly how much power is in use instantly and how much deficit from fully charge you have. By saying your bank has 400 amp hours of capcity and you have used 47 amp hours and are currently drawing 4.5 amps you now know exactly where you stand.

It also means you'll operate your batteries more efficiently because you will know what is really going on. There is money savings in all this. The price of batteries has doubled twice over the past 5 years. You need to make them last as long a possible.

ssullivan · 11-06-2008, 06:46

And....

Be sure your "idiot lights" aren't a sophisticated set of lights indicating state of charge.

I know the Link 10 battery monitor has a bar of "idiot lights" across the top to indicate your battery bank's state of charge quickly and intuitively. They couldn't be more accurate.

Many RVs also have "idiot lights" which are sold as such, but are in actuality, sophisticated battery monitors.

donradcliffe · 11-06-2008, 08:20

I use a radio shack minature digital multimeter, under $20, accurate to +/- 0.02 volts, but I think you are looking for a permanently mounted meter. Be aware that I found a new digital voltmeter installed on one boat which put out enough RF interference to completely wipe out their SSB reception.

After 15 years of watching my battery monitor, I can make a more accurate guess as to the state of the batteries from voltage alone than from their 'amp-hours remaining' display. After a couple of months of discharges and recharges, the amp-hour reading can be off by more than 10% of the battery capacity. Of course the voltage-based guess on the batteries also takes into account the ships load and charging currents from my solar and wind generator.

**GordMay** · 11-06-2008, 09:08

Quote:

Originally Posted by ssullivan

... I know the Link 10 battery monitor has a bar of "idiot lights" across the top to indicate your battery bank's state of charge quickly and intuitively. They couldn't be more accurate.

Actually, the Link 10 Light Bar isn’t very accurate, but the Amp-Hours function is.

The “Link” is a state-of-the-art battery bank monitor that uses sophisticated microprocessor technology to report all significant battery information.
The “Light Bar” is only a quick & rough (5 in 20% increments) indication of battery state of charge. It’s not very accurate. (Ie: the “Full” indication occurs at between 80 - 99% SOC, and the “Mid-Range” indicates between 40 to 59%)

http://www.xantrex.com/web/id/72/docserve.aspx

speedoo · 11-06-2008, 09:32

Tip of the iceberg thread. Especially for those of us who want to learn as much as possible about boat electrics. (my own way of bookmarking)

hellosailor · 11-06-2008, 10:26

Don, beware of the "accuracy" of instruments. While a 420 meter may have a PRECISION of 0.02 units, it will not have that accuracy unless it has been lab calibrated as well.

Most of the less-than-expensive meters are not calibrated vey closely (within 0.1 perhaps) and have additonal errors such as a "float" of 2-3 digits in the least significant digit (LSD, rightmost digit) on the display. Plus an additional error of sometimes 1/2% on any given scale.

So while your meter may show "12.44" for a battery, and show it repeatedly, the real voltage could easily be 12.1 or 12.6. Sometimes the accuracy is important. Sometimes, it isn't. Just knowing "this is a full battery" "this is the normal charge" is enough, and you can approximate down 1/10th of a volt per 10% charge from there--if you are looking at a rested battery, or one in typical light use, so there's no question of surface charge or heavy loads deceiving you.

Voltage? If you read it in context, I'd say it makes a reasonably good charge indicator for several hundred bucks less than one of the total watt/hour monitors. But for some odd reason, you can buy a complete decent multimeter for $20, and a digital display meant to be bulkhead mounted, is $100+.

10-06-2008, 15:31	#1
witzgall Registered User Join Date: Oct 2006 Location: Apex, NC Boat: Westerly Fulmar 32 - Jubilee Posts: 179	good and cheap digital Votage display? HI all; We have idiot lights on our boat showing battery condition. I would like to install a simple digital voltmeter. I know I can buy a Blue Sea or another marine product, but has anyone used a inexpensive meter with good results? If so, what was it? Chris

11-06-2008, 06:38	#4
Pblais Moderator Site Helper Join Date: Mar 2003 Location: Hayes, VA Boat: Gozzard 36 - Bright Eyes Posts: 4,514 Images: 7	Chris, The links posted by Gord are some good ones on this subject. We have a large amount on this topic posted already. Battery monitoring is the key phrase above. What you want is something like a fuel gage for your batteries and that is exactly what battery monitoring is. A volt meter measures only volts and a battery monitor measures power. Power is measured in Volts X Amps X hours. Just knowing the volts is not even close to the correct answer. While a voltage of 10 volts means the bank is toast you don't get clarity from just knowing the voltage. The idiot light can do that for you just as well. Battery monitoing goes so far beyond that by showing exactly how much power is in use instantly and how much deficit from fully charge you have. By saying your bank has 400 amp hours of capcity and you have used 47 amp hours and are currently drawing 4.5 amps you now know exactly where you stand. It also means you'll operate your batteries more efficiently because you will know what is really going on. There is money savings in all this. The price of batteries has doubled twice over the past 5 years. You need to make them last as long a possible. __________________ Paul Blais s/v Bright Eyes Gozzard 36 37 15.7 N 76 28.9 W

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11-06-2008, 06:37	#3
witzgall Registered User Join Date: Oct 2006 Location: Apex, NC Boat: Westerly Fulmar 32 - Jubilee Posts: 179	Right, I understand that. But they would tell us more than three idiot lights, no? Chris

11-06-2008, 06:46	#5
ssullivan Commercial Vendor Join Date: Nov 2004 Posts: 4,533 Images: 1	And.... Be sure your "idiot lights" aren't a sophisticated set of lights indicating state of charge. I know the Link 10 battery monitor has a bar of "idiot lights" across the top to indicate your battery bank's state of charge quickly and intuitively. They couldn't be more accurate. Many RVs also have "idiot lights" which are sold as such, but are in actuality, sophisticated battery monitors.

11-06-2008, 08:20	#6
donradcliffe Registered User Join Date: Mar 2007 Location: Heading south for the winter Boat: Beneteau First 456 Posts: 304	I use a radio shack minature digital multimeter, under $20, accurate to +/- 0.02 volts, but I think you are looking for a permanently mounted meter. Be aware that I found a new digital voltmeter installed on one boat which put out enough RF interference to completely wipe out their SSB reception. After 15 years of watching my battery monitor, I can make a more accurate guess as to the state of the batteries from voltage alone than from their 'amp-hours remaining' display. After a couple of months of discharges and recharges, the amp-hour reading can be off by more than 10% of the battery capacity. Of course the voltage-based guess on the batteries also takes into account the ships load and charging currents from my solar and wind generator.

11-06-2008, 09:32	#8
speedoo Registered User Join Date: Nov 2005 Posts: 226	Tip of the iceberg thread. Especially for those of us who want to learn as much as possible about boat electrics. (my own way of bookmarking)

11-06-2008, 10:26	#9
hellosailor Registered User Join Date: Apr 2006 Posts: 3,283	Don, beware of the "accuracy" of instruments. While a 420 meter may have a PRECISION of 0.02 units, it will not have that accuracy unless it has been lab calibrated as well. Most of the less-than-expensive meters are not calibrated vey closely (within 0.1 perhaps) and have additonal errors such as a "float" of 2-3 digits in the least significant digit (LSD, rightmost digit) on the display. Plus an additional error of sometimes 1/2% on any given scale. So while your meter may show "12.44" for a battery, and show it repeatedly, the real voltage could easily be 12.1 or 12.6. Sometimes the accuracy is important. Sometimes, it isn't. Just knowing "this is a full battery" "this is the normal charge" is enough, and you can approximate down 1/10th of a volt per 10% charge from there--if you are looking at a rested battery, or one in typical light use, so there's no question of surface charge or heavy loads deceiving you. Voltage? If you read it in context, I'd say it makes a reasonably good charge indicator for several hundred bucks less than one of the total watt/hour monitors. But for some odd reason, you can buy a complete decent multimeter for $20, and a digital display meant to be bulkhead mounted, is $100+.