Battery Draw

Discussions regarding electronics, gear and other equipment of maintenance issues that ARE NOT SPECIFIC to a certain PDQ model yacht
John&Ria
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Battery Draw

Postby John&Ria » Tue Aug 20, 2013 9:19 am

This spring we replaced His Idea's four house batteries (believed to be the originals, from 2007) with Trojan T-125's. Better performance was expected - and there has been some improvement - however I am disappointed with the results. The best we seem to get between recharges is about a day, i.e. starting at around 13 volts when fully charged, we get down to 12.0 to 12.2 within 24 hours or so. The primary draw through the day is the fridge (it appears to be drawing about 1.5 - 2 amps), plus occasional use of water pumps and then lights (primarily LED's) in the evening. The Admiral has the fridge set at 4, which may be more than we need, but even then I would not expect the kind of performance we're getting. I've checked the electrolyte levels regularly since we purchased the batteries and they are fine.

Are we expecting too much here, or is there something else going on that needs to be addressed?

Any thoughts/advice from other forum members would be greatly appreciated.

Thanks!

doubledutch
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Re: Battery Draw

Postby doubledutch » Tue Aug 20, 2013 11:14 am

Your numbers sound similar to mine although I don't have the 125s.

Have you checked the charge on the fridge? If it is low (or too high) it could be running for longer periods than necessary.

We have three 75 watt solar panels on the bimini and a 180 watt panel over the davits that keep the batteries topped up without the need for any extra input.

Henry

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eepstein
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Re: Battery Draw

Postby eepstein » Tue Aug 20, 2013 8:06 pm

Hi:

The voltage you are reading is probably the voltage under load, thus it doesn't really indicate the charge level. If you were running your windlass voltage could go down to 10.5 for a few seconds. There are 300 page books written on how to measure true charge with load so I will endeavor not to open a can of worms - as much as I miss some of the old forum debates. :-) If you you were to remove the load for some amount of time, the voltage would rise, but who does that? There are gauges you can buy as well. If you have solar or wind vane, then its even harder tell the actual voltage available.

So here is the no frills way I use: I note the load in amps and voltage periodically during the day. Then use a simple formula of total battery amps/2 gives you the total load you have until its time to recharge. So if you have four 240 AH 6v batteries, you have 240 working amps at 12 volts to get the batteries to half charge (480 total amps of 12 volt power). 8 amps per hour load * 24 hours is 192 amps Which would be about what you would expect on a thrifty power vessel like yours (actual logged amps every couple hours, then added up is more accurate). So your perception may of the batteries being low may only be off by a few hours to about half a day.

If the average during the day is 5 amps you may get two days, if its 10 amps, then 24 hours is all you'll get.

There are a few other older postings that give more detail. And there are lots of books and re-settable amp meters to better manage power. But once you get used to a routine, your routine will be your best gauge.

Last comment, don't underestimate laptop and other 'car' chargers for electronics. They use more than you think when they feed off 12 volts.

Hope I don't awaken the 'old masters' on the forum.

Best,
Eric
Eric & Bonnie Epstein
s/v Desert Star, PDQ36, Hull 49
Annapolis, MD

John&Ria
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Re: Battery Draw

Postby John&Ria » Tue Aug 20, 2013 9:42 pm

Thanks very much for the quick and thoughtful responses. Obviously there is more to this than meets the eye!

The comments about the use of electronics , which we do power through the use of the inverter quite frequently, are well taken. Perhaps our daily draw is larger than we realize.

Overall it would appear our experience is not that unusual, and does not indicate a system problem of some kind, which is good to know. That said, if there are other perspectives out there, they would be most welcome too.

John

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Re: Battery Draw

Postby Tanah-Keeta » Wed Aug 21, 2013 7:02 am

When I had my 36, it was normal to charge batteries about every day and a half.
Ron McDaniel
TK III 34108

duetto
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Re: Battery Draw

Postby duetto » Wed Aug 21, 2013 9:07 am

hi john,

we measure the battery draw with a meter. we know over the years that we consume about 120-150 ah a day. we have an additional engle cooler 1.5 ah draw. so you can see that you get to eric & ron's numbers pretty quickly.

also, most articles reco recharging to get to float phase about every 5 charge cycles.
john & diane cummings
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John&Ria
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Re: Battery Draw

Postby John&Ria » Sat Aug 24, 2013 7:06 pm

Thanks for your input everybody, it was quite helpful. Alas, battery systems will continue to remain something of a mystery, but now I know a lot more than I did before.....John

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Re: Battery Draw

Postby duetto » Sun Aug 25, 2013 6:29 am

hi jon,

if you really want to understand how charge/discharge works, i would recommend a book "living on 12v". don't remember the author but it's the guy who started ample power. they invented echo charger, freedom chargers, etc. it explains charging and usage in great detail but it's readable.

Moderator edit: http://www.rvtechstop.com/articles/lvgrev.pdf
john & diane cummings

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John&Ria
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Re: Battery Draw

Postby John&Ria » Tue Aug 27, 2013 11:11 pm

Hi John,

Thanks for the additonal tip. I'll definitely look into it - sounds like useful bedside reading.

Cheers,

John

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Page 83
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Re: Battery Draw

Postby Page 83 » Sat Sep 07, 2013 9:56 pm

Just for grins, check the seal around the refrigerator door. it doesn't take much of a leak to make it work harder. One way of testing is to scan the seal with a remote temperature gage, $30 on Ebay. Develop a reefer plan to minimize the number of times you open it during the day. We kept a separate cooler to hold things that get used during the day.

I have managed to cruise with a couple chefs on board. [no, I will NOT tell you how I manage to do that! They are great sailors too!] They put the supper stuff on the bottom, lunch in the middle and stuff for grazing on top. There is a latch on the side of the reefer to remind people to keep the door closed. My 12 vdc Engle will freeze several baggies of water during the day when the solar panels are pumping out some watts, and those go into the day cooler. All this is necessitated by an idiot decision to install a side opening rather than top loading reefer.
Sandy Daugherty "Page 83" PDQ 36026

bg5w
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Re: Battery Draw

Postby bg5w » Tue Sep 10, 2013 8:37 am

Sandy,

When you say remote temperature gauge, do you mean the ones where you point at the object, and get a reading, or something that's attached with a wire?

Thanks,
Bob Gruber
Island Time 32

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Page 83
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Re: Battery Draw

Postby Page 83 » Tue Sep 10, 2013 10:46 am

Yuuup. There are several made, priced from $30 to more than $200. Go cheap, there will be more than a couple degrees difference around a leak. It handy to check the temp of the outboard engines' pee-stream, ice in the water tank, cheese on your pizza, asphalt in the tropics (so you don't step out of your flip-flops) and many other useful things.

unofficial old master
Sandy Daugherty "Page 83" PDQ 36026


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