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Old 01-05-2021, 19:16   #1
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Ammeter/ parasitic draw reading

My two 3 month old Trojan T-105's are having serious issues. I charged them fully last weekend. I have been to the boat twice since they were fully charged and have drawn an estimated MAX of maybe 25 Amp hours of power from them during the two days at the boat, almost 100% from LED lights. I'm getting my info from a brand new SG-200 meter. During those two days they have gone from 12.7 volts to 12.3 volts. Either i have one or two bad batteries or another issue.

Iv'e been researching how to test for a parasitic draw and I have a decent multi meter. I was planning on using it to test amp/milli amp draw (if there is any) using the multi meter. My question though is what sort of reading should i expect with everything turned off?

The only 'draw' i should see is a small amount from the LED display of the SG-200. I forget exactly what it is and will have to check, but i'm assuming my reading should match pretty closely with this number. Am i assuming correctly or would it naturally read some slight amperage? Iv'e also read that a reading of '0' is not good because it would indicate that maybe the fuse in the multi meter is blown.
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Old 01-05-2021, 19:41   #2
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Re: Ammeter/ parasitic draw reading

With everything turned OFF, you should have zero current draw however as you stated, you may have some current draw through loads that are always ON e.g. Battery monitor, solar charge controllers etc.

If you have a Charge Bus and/or an Always ON (or Hot) bus, you may find some current draw through the systems attached to such buses.

Happy hunting.
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Old 01-05-2021, 19:56   #3
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Re: Ammeter/ parasitic draw reading

Something is going on. Doubt it is the batteries, but a load that is drawing them down. Keep looking.
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Old 01-05-2021, 20:05   #4
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Re: Ammeter/ parasitic draw reading

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Originally Posted by Wotname View Post
With everything turned OFF, you should have zero current draw however as you stated, you may have some current draw through loads that are always ON e.g. Battery monitor, solar charge controllers etc.

If you have a Charge Bus and/or an Always ON (or Hot) bus, you may find some current draw through the systems attached to such buses.

Happy hunting.
Ok great thank you. I do actually but aside from a rats nest of old electrical its a pretty simple system.
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Old 01-05-2021, 20:47   #5
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Re: Ammeter/ parasitic draw reading

You can read the amps on the sg200 screen. No need for the 2nd amp meter. Assuming it’s installed correctly.

What did the Soc say when the voltage was 12.3?
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Old 01-05-2021, 21:12   #6
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Re: Ammeter/ parasitic draw reading

Thinking aloud, if you have a set (two) Trojans of 6 Volt, and the voltage is as you described, from full to a nearly flat battery, used ~50-60 Amp/hr over 48 hours. If it is an parasitic draw, than you are looking at least at a draw in the order of 1 to 2 amps.
As Smac said above, if the SG200 is connected correctly, that should show on its display. If not, the draw is between that and the batteries. So a multimeter is needed. If it is not a auto range meter, start with the range 10 Amp DC, and switching to a higher sensitivity. Do that at the various points, and see when/where the amp draw starts to occur.
Of course one starts with everything off, as you were toe leave the boat un-attended. As said before likely some circuits will still be on ie bilgepump, solar controller if fitted, radio memory, sometimes anchor light, and of course check how you wired the SG200 monitor itself.
Of course you can check the batteries themselves..... disconnect them for a few days, and if you have more then one set, disconnect each set, compare voltages.
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Old 01-05-2021, 21:25   #7
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Re: Ammeter/ parasitic draw reading

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You can read the amps on the sg200 screen. No need for the 2nd amp meter. Assuming it’s installed correctly.

What did the Soc say when the voltage was 12.3?
Im 100% sure its installed correctly. I figured maybe it was defective?

SOC read 53% at 12.3 volts when i looked at it last night but that was with a 2.5 amp draw. When everything is off it reads 0.00 amps. SOH reads 100% but SOC never seems to stay near 100% for very long, only briefly after charging then drops to 80%. I charge them at 30 Amps for several hours until Amps in drops to .6. I then let them sit a couple hours with charger off then charge them again until acceptance drops under 2%.
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Old 01-05-2021, 21:32   #8
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Re: Ammeter/ parasitic draw reading

The batteries seem to draw down quicly from use only. The voltage remains at what it was when i leave the boat and return even several days later. It just depletes rapidly when there is a draw, even a light one. Im going to pull the batteries tomorrow and do tests with hydrometer and a load test. I suspect a bad battery but dont want to exclude an electrical issue. The mylti meter test i could do quicly before i pull the batteries.

To add...the batteries have been showing diminishing capacity over the course of the three months since i installed them. Its been slow and progressive but noticable. Their usable capaciry has gone from around 100 Ah to maybe 25 at most.I have not been good to them but i dont think my poor charging habits would have ruined them in three months.
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Old 02-05-2021, 09:41   #9
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Re: Ammeter/ parasitic draw reading

The usual suspects for parasitic draw, are damaged chafed insulation on cables, that are causing leakages, current to ground, not enough

to blow a fuse but battery sapping 24/7.

Have you checked the wiring to your bilge pump switch, which may have a problem while sitting in a wet bilge,

Does your bilge pump cycle on/off while you are away from boat.

Do you have any systems on standby, or sleep mode,

Check YouTube for "parasitic draw on car battery"

where you can find out how to find and isolate parasitic draw.


https://www.youtube.com/results?sear...on+car+battery


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Old 02-05-2021, 09:44   #10
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Re: Ammeter/ parasitic draw reading

Does absolutely everything go through your monitor shunt? Engine? Feel your alternator after the engine has been off overnight, if it is warm it is being energized even though the keys witch is off. Another possibility is a bad diode in the alternator.

Your description, although cute, says nothing about your boat so we cannot even guess at what engine you have.
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Old 02-05-2021, 10:10   #11
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Re: Ammeter/ parasitic draw reading

so far, it seems as though the two t105 batts, connected in series, are being treated as one 12v batt. with a dvm, one can measure the terminal voltage of each batt while the two are installed in the usual way. the batts should have nearly identical terminal voltage, the sum of which should equal what is measured across the two in series. if the measured terminal voltage (taken with no significant load on the batts for at least 30 min. and measured on the batt terminal, not something connected) are not the same (within 0.05volts), then it is likely the batt with the lower terminal voltage reading has an issue. if the measured voltages are equal, then it is likely the problem is elsewhere in the form of a unknown current draw.
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Old 02-05-2021, 10:16   #12
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Re: Ammeter/ parasitic draw reading

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Originally Posted by BAD ORCA View Post
The batteries seem to draw down quicly from use only. The voltage remains at what it was when i leave the boat and return even several days later. It just depletes rapidly when there is a draw, even a light one. Im going to pull the batteries tomorrow and do tests with hydrometer and a load test. I suspect a bad battery but dont want to exclude an electrical issue. The mylti meter test i could do quicly before i pull the batteries.

To add...the batteries have been showing diminishing capacity over the course of the three months since i installed them. Its been slow and progressive but noticable. Their usable capaciry has gone from around 100 Ah to maybe 25 at most.I have not been good to them but i dont think my poor charging habits would have ruined them in three months.
Some draw is normal as said.
Sounds more like your losing capacity as you've mentioned.
I'm betting one or more of your T-105s are losing capacity.
I think your on the right path though.
Separate the units electrically, then test each cell with the hydrometer.
I think you'll find significant comparative differences.
Are your Batteries dated? Hopefully there all the same age.
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Old 02-05-2021, 11:18   #13
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Re: Ammeter/ parasitic draw reading

I ran a bunch of numbers, and my guess is it's a bad cell or 2 in the bank of Trojans, although it can still be a parasitic load some where.

Diminishing capacity over such a short time also indicates bad cells.

Hygrometer or volts by cell when at the 12.3V level should show any bad cells in the bank.

Happy hunting,

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Old 02-05-2021, 13:09   #14
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Re: Ammeter/ parasitic draw reading

The one thing you need to be absolutely sure of is that the shunt for your SG200 is absolutely the last part of the negative bus before return the the negative battery pole - and there are absolutely no other negative ground wires attached to the negative ground terminal itself.
If there is any circuit whatsover that bypasses the shunt, you are not measuring the entirety of your electrical system.
Then also be aware that the SG200 ammeter reading is also subject to possible zero error.
The app for my Victron BMV-712 allows me to fiddle with the zero offset error. Whether or not this actually improves accuracy can be debated, but I for one am not having battery problems - knock on wood:
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Old 02-05-2021, 17:37   #15
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Re: Ammeter/ parasitic draw reading

Thanks everyone for chiming in. Lots of good things to think about. I will try and answer as much as i can but today has been my only day off and its been a busy one.

I pulled the Trojans and threw in a little West Marine dual use battery i had lying around to get me through the week. I couldn't find a hydrometer so will have to order one off Amazon and test the Trojans later this week.

Before i pulled the Trojans i did a quick test for parasitic draw. With the battery selector switch set to 'off' i have a draw of .004 amps. When i turned the selector switch to 'on' the draw went up to .134 amps. Not a huge amount and one i can live with temporarily until i can rewire the distribution panel.

Andy the shunt is the last part of the negative bus, the only other wire connected to the negative terminal on the battery is the battery temp sensor for the charger. The neg battery cable goes directly to the shunt and from the shunt to the DC neg bus. I manually turn the charger on and off so the temp sensor shouldnt interfere. That being said, there are still a couple of old, yet undetermined ground wires connected to the engine. One of them im pretty sure is the AC earth ground. One other i believe might be the old courtesy lights which do work with everything switched off. I think there is one more. I will remove these soon and consolidate them on my DC- bus bar.

The distribution panel is a horrid mess with many wires untraceable. Multiple soldered wires stacked and soldered together, trailer connectors etc...
Considering how bad it all looks im surprised its not worse. This will all start to get sorted out soon. Im hauling the boat next month for some big projects. Once im back in the water the distribution panel is next. I'm going to rip everything out and start from scratch. If one of the Trojans turns out to be bad i may just leave well enough alone. If both T-105's are good i guess i'll try to dig a little deeper as time permits. I dont think my situation is dangerous...
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