Low battery voltage ?? E7 problem??

[djneedham24]

My boat has 2 x200 Ah batteries as the house bank. These are apparently wired as 1x 400ah battery so I cannot use them as a 1 and 2 configuration.
On my return to the boat after 5 months away I noted

When using by bowthruster./winch etc , any large DC user the Raymarine E7 would drop out. I presume on low volts. A quick look at the link when using the Bowthruster showed a drop to +- 9.5 v.

I conducted a little test on the two batteries as one "all" ie 400 ah cap

time DC amps AmpHrs Volts
start 12.5
12.44 -38.2 -8.3 11.45
13.16 -37.3 - 28.1 10.90
13.26 -36.9 -34 10.75
13.38 -36.5 -41.5 10.5
13.48 -7.5 -42.5 11.9 reduced load
13.55 -1.7 -44.6 12.3
14.19 -1.3 -45.2 12.35.

So what does that tell me.
Should a DC load drop the battery voltage that much?
sufficient to trip the E7 on low voltage?
I am guessing this is why it trips, however I can make it trip just by pressing the bowthruster button !
Is it the batteries or is it the E7?

[djneedham24]

sorry guys despite editing it twice it still garbles my columns of figures
basically a load of 37 amps drops battery voltage to 10.5 volts over about 1 hour.Reducing load to 7.5 amps batt voltage goes up to 11.9. If I switch off virtually everything; batt voltage goes to 12.3 (Start 12.5)

so battery problem ? E7 problem ? or both !

[S/V_Surya]

I am guessing dirty connections somewhere. Start at battery. Not enough contact to pass the required current. How old are your batteries? Maybe they cannot hold the charge.

[sailorchic34]

Well if the batteries are in good condition and full changed then you should have 12.7-12.8 volts at full charge. If you only have 12.5V at full charge either your batteries are old/defective, the battery charger is defective or your volt meter is off. 12.5 volts is about 80% charged.

You will get a voltage slump on the batteries when using heavy loads and when used. You'll get more of a slump if the batteries are old or if the wire connections to the panel, load and battery are corroded.

Some recommend that bow thrusters and windlasses have their own battery so that the house bank is not overly depleted by high amp draws...

[djneedham24]

Batteries came with the boat and are dated sept 2007

[S/V_Surya]

Clean all your connections and test again. If it is still doing it, probably batteries need replacing.

[foggysail]

Have you measured the batteries' specific gravity? Without that information, you have no clue to the batteries' condition.

MainSail has somewhere time, voltage load current data he put great effort into compiling. Search his posts for this data.

Another comment-- if you are not using a good three stage charger, I doubt your batteries ever get to full charge.

[daddle]

The batteries are on the old side. But it sounds more like a bad connection.

The battery voltages listed by SailorChic above are for the chilly conditions of SF Bay Here in paradise the normal voltages are considerably lower.

I would like a separate battery for the electronics rather than a separate battery for the windlass and such. It is a drag when a stall in the windlass resets the instruments.

[marshmat]

Foggysail's right, you need to poke each cell in that bank with a hydrometer. It's hard to trust your monitoring instruments after a few main bus undervolt conditions.

Are you measuring voltage directly from the battery studs, using dedicated sensing wires?

It is quite possible (indeed, likely) for the situation you describe- dramatic voltage drops at high current- to be related to a corroded, loose or undersized connector.

It is normal and expected for computers, such as your E7, to shut down with this kind of voltage drop.

[Dsanduril]

Originally Posted by djneedham24

...On my return to the boat after 5 months away I noted...

What type of batteries and how were they maintained for the 5 months you were away? If they are Lead-Acid (LA) they are subject to significant self-discharge, and if left alone (uncharged) for 5 months this could lead to sulfation, which in turn could lead to the performance you are indicating.

I would recommend a full equalization charge (after checking/filling water levels if wet type batteries) to see if you can bring them back. 5-year-old batteries that have not been attended it's probably an even money bet. If they were on a maintenance charge of some kind I'd still do the equalization, that should get you a full charge and help somewhat. If it doesn't then time to replace.

[sailorchic34]

Originally Posted by daddle

The battery voltages listed by SailorChic above are for the chilly conditions of SF Bay Here in paradise the normal voltages are considerably lower.

Hum... Thats not quite how I understand it but then I do have blonde moments now and then. However attached is a temperature compensated battery measurement table....

Google Image Result for http://www.meeknet.co.uk/e38/E38_Battery_SOC_Table.jpg

[DeepFrz]

Guys, if measuring the voltage at the battery posts a bad connection in the load line will not affect voltage drop. You will only see excessive voltage drop on the load side of the bad connection.

However this is another "20 questions" post and without a lot more information can't be answered.

[sailorchic34]

Originally Posted by DeepFrz

Guys, if measuring the voltage at the battery posts a bad connection in the load line will not affect voltage drop. You will only see excessive voltage drop on the load side of the bad connection.

However this is another "20 questions" post and without a lot more information can't be answered.

+1.

Exactly. If the OP is measuring at the battery posts then the drop is due to poor cell capacity. With a 5 year old battery, Its very possible that the battery(s) are older and down on the capacity. Of course if the terminals / connects are corroded on the circuit path to the electronics giving the under volt alarm then it could be caused by both tired batteries and some corrosion on the electronic circuit side.

[daddle]

Interesting. And very much conflicts with my reference which says:

"All voltages are at 20 °C (68 °F), and must be adjusted −0.0235V/°C for temperature changes."

This will require some study.

[Dsanduril]

Originally Posted by daddle

Interesting. And very much conflicts with my reference which says:

"All voltages are at 20 °C (68 °F), and must be adjusted −0.0235V/°C for temperature changes."

This will require some study.

-0.02V/°C +/- is pretty typical for the change in charging voltage per °C. Considerably less than that for measuring state-of-charge by open circuit voltage (depends on the battery, but around an order-of-magnitude lower).

If measuring voltage drop at the battery posts with a bad connection downstream there will still be somewhat more loss of voltage than anticipated because the current will likely go up to compensate for the downstream voltage loss. Not the same as measuring at the load, but still something to note. Knowing what the current draw of the thruster/load was/is supposed to be would help.