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Catalina Direct Discussion Topics / Catalina 22 Discussion Area / Electrical / Voltmeter vs Ammeter
 
 
Author Voltmeter vs Ammeter
Sean Madian
Portland, OR

Boat Name: Time Out

Model/Year: 1973

Hull No. CL 3839 FX

Hailing Port: Portland
12/06/2005 5:20 PM Pacific Time

I've heard two different suggestions re. onboard power monitoring and management. Volts is good to monitor batt discharge but amps is really the measure of what you've got availble. What are people using and why? If you're using a built in meter have you gone w/digital or analog and where did you get it?
Colin Abbey
Penticton, British Columbia

Boat Name: Will o' The Wisp

Model/Year: 1978

Hull No. 8276

Hailing Port: Penticton
12/06/2005 10:36 PM Pacific Time

A multimeter (measures Volts, amps & watts) is the way to go. Digital is more precise than an analog one. Can be had for approx $25 from most hardwares or Walmart etc. A meter that can measure amps is a must as you should be able to list how many amps each of your loads draw. This will help you determine how much you will drawing from your battery (and consequently how long you can draw it for according to your batteries' amp-hour rating. Make sure that its a 'deep cycle' battery, the heavier the better. Boat use will murder an automobile battery. Hope this helps somewhat.
Karl Mielenhausen
New Bern, NC

Boat Name: Impromptu

Model/Year: C22 1985

Hull No. 13021

Hailing Port: Northwest Creek Marina
12/07/2005 5:08 AM Pacific Time

Keep in mind the difference between 100% charged wet cell battery and 50% charged is only 0.63V (12.63 vs 12.00). 100% discharged takes you down to 11.64.
Must be read with all loads OFF for at least 10 minutes. And no sooner than 24hrs since any charging, in order to avoid surface charge error.
Also, your $20 multimeter might not be accurate, so build yourself your specific correction table.
Al Gearing
Burleson, Texas

Boat Name: Torch of Freedom

Model/Year: C-22/'76

Hull No. 6448

Hailing Port: Arlington YC
12/07/2005 5:34 AM Pacific Time

Remember that to measure amps you have to put the meter in series with the load, which is hard to do except for one in series with your battery. Multimeters can measure volts or amps but most cannot do both at the same time to measure power, volts x amps. I think the advice to just conserve power is the best. Hand held drycell operared VHF and GPS should be enough for most trips, you don't have to have the GPS on continually, what would you do if you didn't have one? Use dead reckoning, compass heading and estimated speed, until you are in close, in the dark, you won't be looking at your GPS much anyway, turn it off. A deep cycle battery with over night re-charge, as reccommended above is really the simplest I think.
Al Ge
Sean Madian
Portland, OR

Boat Name: Time Out

Model/Year: 1973

Hull No. CL 3839 FX

Hailing Port: Portland
12/07/2005 7:27 AM Pacific Time

Thank you all. Colin, what is your thought around gel vs flooded? I like the idea of a multimeter but to Karl's point, should it always be digital given the small variations in voltage we're trying to capture? If the voltage swing is 12.63 to 11.64 volts then every tenth of a volt counts doesn't it? Al, I agree with you and assume there is some way to wire the multimeter through an appropriately sized DPDT (or similar) switch so that you can put the meter in-line for amperage and then across the terminals for voltage. Perhaps I'm going into overkill here but then again aren't we all just a bit geeky about our boats???
Al Gearing
Burleson, Texas

Boat Name: Torch of Freedom

Model/Year: C-22 '76

Hull No. 6448

Hailing Port: Arlington YC
12/08/2005 8:00 AM Pacific Time

If you try to use multimeter that way, w/DPDT, you wil find that the connection on the meter are different for a voltage reading and amp reading. Really, just look at the simple little ammeters use on cars since the Model T, and if you want, wire one in. In the 15 years I had the 35' with an inboard deisel and 55 amp alternater, I never needed an ammeter, even with two batteries, one for engine starting, the other for house/nav/radio use. A simple voltmeter with a limited range, as used on modern cars, mounted in a panel will tellyou when you need to think about getting your batteries charged. But regulators will stop, or just keep them fully charged, for you whether from motor driven or shore power. Remember KISS, and enjoy sailing.
Al Ge
Colin Abbey
Penticton, British Columbia

Boat Name: Will o' The Wisp

Model/Year: 1978

Hull No. 8276

Hailing Port: Penticton
12/21/2005 6:13 PM Pacific Time

Hello Shaun: Apologies for not replying to your post of the 7th. re what battery I use. Right now i'm trying to do due diligence before making my next battery purchase. I'm not an expert by any stretch of the imagination but I'm trying to clue myself in as best I can, and this format has been extremely helpful. I would like to relate what a well-known marine surveyor wrote about gel batteries.as I believe you were considering one. "Batteries develop heat when charging, as well as hydrogen gas. For this reason, the (battery) needs to be in a well ventilated area. Gel cells are particularly vulnerable to overheating damage. Putting gel cells in covered plastic boxes has proved to be a problem, and for this reason they are falling out of favor. Sometimes improved technologyisn't an improvement after all". -end-. I hope this helps.
Sean Madian
Portland, OR

Boat Name: Time Out

Model/Year: 1973

Hull No. CL 3839 FX

Hailing Port: Portland
12/22/2005 5:49 AM Pacific Time

Hello Colin -- Thank you for the post (BTW, great name for your 22). I'd read the same thing and I intend/hope to leave the battery aboard w/a semi-permanent charging system. Here's what I am leaning towards: installing an all weather reverse plug in the cockpit liner to plug in shore power; using a shore power plug w/built in 15 amp GFCI; adding a Quest or other 5-10 amp charger; installing one-or-two flooded but sealed batts.

The one-vs-two batts debate has two elements. First, amperage and second voltage. Assuming I want to get to around 150 amps total it has been suggested that two batts at 80-90 amp is better than one at 150. Why? Because if I drain out 75 amps from the 150 then I'm at the magical 50% mark whereas if I drain 75 from two 80s or 90s that I'm further away from having drained them to 50%. Of cousre, that means I have to purchase/install two batts, use a batt selector (possibly), double my wiring, etc.

The second debate touches on the first w/some suggesting that two 6v batts wired in series is superiod two on 12v.

I'm heavily leaning towards a single 150 amp batt. I was shown a flooded batt last weekend that had sealed caps. I've also been told that in some cases the flooded batts don't need to have their caps removed during charging but I don't think I believe that. Finally, I've been told that charging a flooded batt in a boat can create harmful and very corrosive vapor in the boat (not to mention the danger of acid spills in the case of a knockdown). Still more research to do.

I'd be curious to know what you decide in the end.
 
 
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Catalina Direct Discussion Topics / Catalina 22 Discussion Area / Electrical / Voltmeter vs Ammeter