Low voltage when running accessories

[BassMan11]

As I sit here in Ottawa dreaming about open water fishing I always like to think about things I can do to my boat. Last year I was running into some low voltage issues on my house battery when everything was running. Aerator, livewell pump, HDS 12 and 7, Lowrance sonic hub, NMEA 2K and lights would drop the voltage to around 11.5 and set of the Lowrance low voltage alarm. Obviously turning a few pumps off would bring the voltage back up to 12-12.3. I have a dedicated group 24 agm battery (largest I can fit) for a accessories only. This battery is brand new and runs to a rocker panel on my Lund. Is this just something that will happen when running that much load or could there be another issue such as wire gauge or something?

Reaching out out to the master minds on this site for sound advance as per usual. Thank in advance  

Don

[G.mech]

I'm sure you'll get lots of advice but I'd look at the wire size to your accessory panel for starters, you have quite a bit of stuff running and the HDS units do draw a fair bit of power themselves.  The first thing I would do though is adjust the alarm voltage setting in your 'Settings' - 'Alarm' menu to stop it from going off so much.  That would drive me nuts. 

[Garnet]

Brand new battery's are most likely to fail.

Everybody with a boat should have a load test $50 at CTC. 

[DanD]

If all our electronics are running normally, with them all on (Until voltage drops) the wire size to them are fine. I would put an ammeter between all out going current from the battery; turn all equipment on. Record that value and then connect the ammeter between in coming charge current from the engine's charging system. If the voltage used is above the charging systems capacity; you will slowly drain the battery, The charging system just cannot keep up to the demand. If I'm correct in this thinking; you have a couple of options. See if there are larger or more charge coils that could be added to the engine's charging system. Or add a second accessory battery, wired in parallel. Kind of like hooking booster cables between to cars. With the second battery, you will still eventually drain both batteries; but that'll give you twice the capacity and time to run all your electronics. There would be another test I would perform; move the ammeter from the battery's charge wire to the engine's output charge wire. If there is a 5 or 6 amp difference between the two; you could try a larger cabling between the charging output too the accessory battery. Without doing the tests; I believe you'r just using more voltage then the engine's system can replenish.   

Dan.

[G.mech]

Are you having trouble when the engine is running or shut off?  Two different scenarios as Dan suggests.  If the wire to your panel is sized properly you should have no more than 10% voltage drop (1.2V)  , between the battery and your panel and preferably 5% (o.6V) with everything running.   

Edited February 24, 2018 by G.mech

[BassMan11]

I have a load tester and the bettery is fine from that standpoint. The house battery is separate from the starting battery so it is not being charged at all out on the water. Also I am on the trolling motor most of the time anyway. But even after a fresh charge on the house battery if I flip everything on it drops the voltage. The alarm on the HDS doesn’t make a sound but just flashes on corner of the screen. Running them in parallel is tough since the batteries are not in the same hatch but I have thought of trying that. I have done some tests with with a multimeter and the voltage reading on the HDS screen runs true with that I am getting at the battery. Maybe it’s just battery size? Thanks for the replies so far. 

[DanD]

So with accessory battery not being charges buy the engine; you need to increase your power capacity.  A second battery, that can be located anywhere on the boat. A minimum of 12 gauge or larger cables between the two..

Dan

[BassMan11]

Ok Dan so if I am hearing you right if I have another battery wired in parallel to the house battery it will increase the capacity and therefore the voltage will not drop as much?

[aplumma]

As Dan D said if you measure all of the amps being drawn by putting the amp meter between the battery and the load as you turn on each item it will give you an amp draw for each accessory. After turning each on and off add up the numbers. now turn on all of the accessories at once and it should be the same number. This is know as the load on the battery. The load on a battery is the amps on how much reserve you have. So if yo u have a easy numbers 500 amp battery and a 10 amp load in theory you have 50 hours from 100 percent to 0.  If you have a second 500 amp battery it becomes 1000 amp hours drawing down at 10 amps or 100 hours. Kind of like feeding an outboard motor off 2 gas tanks it will take twice as long to reach 75% of the fuel on the gauge. This keeps you in the 12-12.6 range of the voltage twice as long. A battery just unplugged from a charger should read 13.2 13.4 after 1/2 hour it should read 12.6 as the final charge. Voltage testing is not as good a test as a battery hydrometer  

Art

 

[BassMan11]

Art that makes sense. So if I wire in another battery in parallel do I need a selector switch or can you just wire everything directly. I did a quick drawing of what I think it would like like without a selector ( I can’t draw)  Batteries are both 2017 CT AGM deep cycles with similar production dates  

 

Also I have a hydrometer but they are sealed AGM batteries. 

 

Edit. There is a fuse from the rocker panel as well. 

Edited February 24, 2018 by BassMan11

[G.mech]

   Here's the thing, you can hook as many batteries in parallel as you like you will still only have 12.6 volts to work with even though you have more power capacity to run the stuff for longer.  If you try and draw too much current through too small a conductor (the wire from AGM-1 to the switch panel and back), the resulting voltage drop will be too high for your electronics to operate properly.  If you're losing 1.6 Volts through the undersized conductor and you're starting with 12.6V, you will only have 11 volts left at your devices regardless of whether you have 1 battery or 10.  Until you turn off some of the devices to reduce the load (which I think is what your describing) you will have low voltage at your dash.  

     If your battery is simply running out of juice, that's another story and adding more batteries will keep them running at full voltage for a longer period of time as Dan and Art are suggesting.  

   Here is a wire size chart for 12V marine electronics, I'd check the wires to your dash panel and make sure they're big enough for the load before going to all the extra batteries.  Remember, the length shown is for the wire both to the panel and back to the battery so if it's 10 feet away, you use the 20 foot length at the left of the chart.  I usually run at least a #10 to the dash to run all the electronics, most boats from the factory have a much smaller conductor and lots of people have the same trouble:

Edited February 25, 2018 by G.mech

[chrisb]

You need to measure the voltage at the battery when this happens. If the battery voltage is low then the battery is not able to support the load. If the battery voltage is good then as already stated you need larger cables to the power distribution panels.

[BassMan11]

G,

Totally get what you are saying and that’s always what i thought was that the voltage doesn’t change so how do you stop the drop? I checked the boat and I have 10 gauge wire from the panel to the battery at about 6’ max. 

 

 

 

[G.mech]

5 minutes ago, BassMan11 said:

G,

Totally get what you are saying and that’s always what i thought was that the voltage doesn’t change so how do you stop the drop? I checked the boat and I have 10 gauge wire from the panel to the battery at about 6’ max. 

 

 

 

I'm not sure what all you have connected or the total amperage with everything running but I would think the #10 should do it especially being that short (it would give you about 25A capacity with a .4V drop).  Are the grounds all connected back to a ground bus with a #10 running back to the battery too?  The negative leg is just as important as the feed to switch panel and should be the same size.  If the battery voltage is up to snuff, I'm not sure what else to look for other than maybe a loose or dirty connection and confirming the actual loads with an ammeter as others have said just to be sure. 

    One thing you could try is running another parallel feed wire temporarily from the battery to the switch panel and see if the voltage drop goes away with both of them connected.  If that stops the drop it stands to reason that the feed may in fact be undersized but I really can't see it unless you have a very large load. 

[DanD]

Here's a way to test the cables without having to remove them. Connect a voltmeter between (like in the pic) the switch positive and the device positive. The reading on the meter should show 0 (zero). Now turn the device on and read the voltage on the meter. Whatever the reading is, is the voltage lost passing through the cable. Rule of thumb is .25 (1/4) volt maximum. This is called a voltage drop test; a resistance test on a live circuit.

In the picture I'm showing that the green wire is being tested. Anything near or above this 1/4 volt would be considered hight resistance. Which could be caused by a bad connection, bad or undersized wire. The voltmeter can be moved/connected anywhere in the circuit; including the ground side of; same rules apply.

Dan

[G.mech]

4 hours ago, DanD said:

Here's a way to test the cables without having to remove them. Connect a voltmeter between (like in the pic) the switch positive and the device positive. The reading on the meter should show 0 (zero). Now turn the device on and read the voltage on the meter. Whatever the reading is, is the voltage lost passing through the cable. Rule of thumb is .25 (1/4) volt maximum. This is called a voltage drop test; a resistance test on a live circuit.

In the picture I'm showing that the green wire is being tested. Anything near or above this 1/4 volt would be considered hight resistance. Which could be caused by a bad connection, bad or undersized wire. The voltmeter can be moved/connected anywhere in the circuit; including the ground side of; same rules apply.

Dan

 

That's too easy Dan.......good idea!

[aplumma]

15 hours ago, BassMan11 said:

Art that makes sense. So if I wire in another battery in parallel do I need a selector switch or can you just wire everything directly. I did a quick drawing of what I think it would like like without a selector ( I can’t draw)  Batteries are both 2017 CT AGM deep cycles with similar production dates  

 

Also I have a hydrometer but they are sealed AGM batteries. 

 

Edit. There is a fuse from the rocker panel as well. 

your drawing is correct they are both charging as well as feeding the panel.

 

Art

[Garnet]

This is mostly for other people reading I'm sure you know this.

It's critical that all your connections are shinny clean and covered it white grease.

 

[fisherman7]

I had the same problem when I was taking a 12v feed from my 24v trolling motor setup. After a few hours on the TM I'd lose my electronics. I switched the feed to the 12v starter battery and haven't had a problem since. 

[AKRISONER]

would installing a decent capacitor perhaps assist with smoothing out the load? Just speaking from my car audio days.

[BassMan11]

OK so an update. I got out into the garage and starting screwing around and testing a few things. It looks like I am sitting at 12.1 volts at the battery when I have every accessory on in the boat. At my fish finder (at 100% brightness) I am reading about 11.6 depending on volume of the Sonic hub. Once I turn everything off except for the fish finder and sonic hub the battery is sitting at 12.3 and the fish finder is reading at about 12 volts. All battery terminal connections were cleaned and re-seated. Is that acceptable drop through the fuse panel? If not I guess I know where the issue is... which is unfortunate because its a nightmare to work. 

[DanD]

If you could do an actual voltage drop test; that would tell us if it's the feed circuit (wiring, switch or splices) to the fish finder or whether that's what the finder is using. Connect the meter's positive lead to battery positive. Connect the meter's negative lead to the fish finder's power wire/connector at the finder. Turn the finder on and take a voltmeter reading. If you have more then the .25 volt reading (voltage drop) there, move the meter's negative lead back (towards battery) to the next connection and take another reading.  As you move back towards the battery and there's a drop in voltage, too lets say down to 1.7 volt. You know the issue is between this test spot and the last. Also test the ground side, in the same manner. A bad ground is just as bad as a power feed issue.

Dan.

[G.mech]

    That is quite a voltage drop, not ideal for your electronics.  You could turn down the voltage alarm setting on your HDS down to 10.5V and go fishing since your HDS units will keep working down to about 10 volts but as your battery runs down your voltage is going to continue to drop which may cause problems.  If you do the tests Dan describes and you find it is a feed wire size issue, you could just add a second parallel conductor (say a #12) to your exist #10 feed and ground and it would reduce the drop considerably rather than replacing the #10's altogether if that's easier. 

    On my last 2 boats, I put a separate fuse block in at my console for my dash electronics completely independent of the livewells, lights and stuff.  I fed it from the house battery with a #10 and haven't had any issues at all but it's surprising how all the loads add up on this stuff with it all combined.   May be something to consider since it sounds like you've got quite a bit of stuff connected. 

Edited February 26, 2018 by G.mech

[Garnet]

When you get this sorted out.

I use the sleep mode a lot.

Whitby Marine is where I buy really good stainless buse and 6 gauge  wire with soldered ends and run that to my dash. Spending 1000's on finders and doing a bad install is common.

[chrisb]

On 2/26/2018 at 9:21 AM, AKRISONER said:

would installing a decent capacitor perhaps assist with smoothing out the load? Just speaking from my car audio days.

Not when you are running off a battery. You can't get any smoother than pure battery power.