Battery monitor showing different Volts than main panel + how to setup AmpHRs

[simonpickard]

Hello all,

I just done installing my fancy new Victron Energy 700 battery monitor. So far so good. Seems to be working well. One thing I've noticed is that the monitor always shows about .4volts less than the boats built in volt gauge on it's control panel.

Any ideas why they are showing different voltages? Shouldn't these be the same?

Also, the 700 asked for the capacity of the batteries. I have 2 x 165AmpHr Gel house batteries which look to be wired in series so I put that I had 330AmpHr's. Is that correct?

Regards,
Simon

[HappyMdRSailor]

Simon,

I can fix the display problem with one small piece of electrical tape...



Wired in series gives you AH1+AH2/2

You also need several reductions in your rated AH for a proper setting...

edit: many gurus here way more qualified than me...

[svinshallah]

When you series connect batteries, the voltage of the two is added, the AH rating is the same as one battery.

If the voltage measured AT the battery, where the Victron reads it, is more than the voltage shown at the circuit breaker panel, then either the panel voltmeter is reading incorrectly (very common when you have analog meters) or you have voltage drop in the wiring between the battery and the panel.

[colemj]

Your panel voltage meter may not be calibrated correctly. Also, many panel meters measure the voltage at the panel feed, while battery monitors measure the voltage at the batteries themselves. Perhaps you have a poor main connection to the panel?

Mark

[simonpickard]

I think they are series. I can see a metal bar between both red positives linking the two batteries.

So it should be set to 165amp hrs? Not 330?



Please visit my blog:
www.sailing-interlude.com

[Night_Sailor]

Originally Posted by simonpickard

Hello all,

I just done installing my fancy new Victron Energy 700 battery monitor. So far so good. Seems to be working well. One thing I've noticed is that the monitor always shows about .4volts less than the boats built in volt gauge on it's control panel.

Any ideas why they are showing different voltages? Shouldn't these be the same?

Also, the 700 asked for the capacity of the batteries. I have 2 x 165AmpHr Gel house batteries which look to be wired in series so I put that I had 330AmpHr's. Is that correct?

Regards,
Simon

I have two Victrons--I am about to pick up a second one and I'm glad I had left over wire from the last installation. They make these for Linksys, and I later discovered they are cheaper direct from Victon and bought another one.

Victron is the only way to go for these. I like them. But you should have a charging source for the batteries, like a solar panel and charge controller, as these devices will draw a battery down if left on for months with nothing to keep the batteries topped off. The Victon battery monitor will use some power, but it should be less than .1 A, yet it must be connected at all times, so the solution is to have a solar panel hooked up to your battery.

You should configure the Victron for 165 AH and I presume 24 Volts.

The boats built in volt-meter is more likely in need of adjustment. Test with a portable VOM and verify that. There is a screw on front you can use to fine tune it.

There could be an issue with the terminations at the batteries, the shunt, or one of the other connectors. Trace the wires from the built in Battery monitor also. Do they go directly to the battery? If so you might want to take the negative lead to the ground bus at the shunt instead of the battery ground. There is a difference between battery ground and vessel ground. I would use the shunt for vessel ground. On the shunt, use the side away from the battery for vessel ground and connect a grounding bus to that.

[Night_Sailor]

Originally Posted by simonpickard

I think they are series. I can see a metal bar between both red positives linking the two batteries.

So it should be set to 165amp hrs? Not 330?



Please visit my blog:
www.sailing-interlude.com

If the bar connects the two positive terminals then you are not in series but in parallel. There should also be a connection between the two negatives. It may be two heavy cables going to a common ground point like the shunt. The shunt looks like this:


In this case your AH setting should be 330 AM and the voltage set at 12 V.

Note the picture shows this boat was incorrectly wired. Both battery bank negative grounds must go to the same side of the shunt--battery ground (right side). The shunt is used to measure all the current flowing into and out of the batteries--that is why there is a battery side and a load side. All the loads go to the other side--that is vessel ground (left side of shunt).

Often batteries are sold with a single straight bar that connects the positive of one to the negative of the other. Is the bar straight? That would be a series connection. In this case the voltage would be 24 V and the AH setting would be 165.

You might want to post a few pictures or hire a competent marine electrician if you are unsure if this is wired for 12V or 24 Volts.

[Night_Sailor]

Originally Posted by HappyMdRSailor

Simon,



You also need several reductions in your rated AH for a proper setting...

edit: many gurus here way more qualified than me...

He makes a good point. If the batteries are old, they may not provide the full rated capacity. For example, I have an old 8D Gel Cell battery that is rated for 225 AH. It actually has a capacity of about 100 AH. If placed under heavy load that drops to about 75 AH. Ratings are typically for new batteries, and a 20 hour discharge rate.

If your batteries are old, you might have to guess at a lower rating or risk discharging them too deeply. You can estimate the capacity by studying the voltage and measuring using your Victron battery monitor how many Amp Hours are used under normal load before the Voltage drops under 12 Volts. I would avoid dropping the voltage below 12 Volts if you want long life out of your batteries.

I presume your batteries are new if you installed a battery monitor.

[Night_Sailor]

You need to ignore the color of the cables in the bank some times. People may use all red cables even though some of the cables might be more accurately defined with black for the negative sides.

In some cases sold metal bus bars are used to join batteries in series. I don't think I've seen that used in parallel but it might be appropriate in confined spaces as heavy cable is hard to bend and fit at times.

Below is an example of two pairs of 6 Volt batteries in parallel with a second bank of two. So the result is 12V at a higher AH capacity. This is common for people who use golf cart deep cycle flooded batteries. It is a cheaper way to gain capacity, but they require some maintenance topping up the cells with distilled water. In this case short red cables are used to jumper the negatives of one 6V battery to the positive side of the other.


An example showing series and parallel wiring. Both are 12V systems, one uses 6V in series, the other 12V in parallel.

[Maine Sail]

Originally Posted by Night_Sailor

In this case your AH setting should be 330 AM and the voltage set at 12 V.

Note the picture shows this boat was incorrectly wired. Both battery bank negative grounds must go to the same side of the shunt--battery ground (right side). The shunt is used to measure all the current flowing into and out of the batteries--that is why there is a battery side and a load side. All the loads go to the other side--that is vessel ground (left side of shunt).

Please don't poach my image then tell folks that the boat was "incorrectly wired". That vessel is 100% CORRECTLY WIRED!!!!

Bank #2 is the starting battery, bank #1 is the house bank which is the only bank the shunt is monitoring. Banks #2 MUST be on the load side of the shunt for the house bank to be accurately monitored.

If you don't understand the wiring, in the image you poached to make your point, then please don't poach others photos and tell folks it is "incorrectly wired" when it is 100% correctly wired... Sheesh.....

Originally Posted by simonpickard

Hello all,

I just done installing my fancy new Victron Energy 700 battery monitor. So far so good. Seems to be working well. One thing I've noticed is that the monitor always shows about .4volts less than the boats built in volt gauge on it's control panel.

Not uncommon at all:

#1 Where are both volt meters sensing B+?

#2 Where are both volt meters sensing B-?

#3 Volt meter #1 could be out of calibration

#4 The Victron may not be 100% accurate either but it is usually a lot closer than the volt meter the builder threw in....

[Night_Sailor]

Originally Posted by Maine Sail

Please don't poach my image then tell folks that the boat was "incorrectly wired". That vessel is 100% CORRECTLY WIRED!!!!

Bank #2 is the starting battery, bank #1 is the house bank which is the only bank the shunt is monitoring. Banks #2 MUST be on the load side of the shunt for the house bank to be accurately monitored.
If you don't understand the wiring, in the image you poached to make your point, then please don't poach others photos and tell folks it is "incorrectly wired" when it is 100% correctly wired... Sheesh.....


Not uncommon at all:

#1 Where are both volt meters sensing B+?

#2 Where are both volt meters sensing B-?

#3 Volt meter #1 could be out of calibration

#4 The Victron may not be 100% accurate either but it is usually a lot closer than the volt meter the builder threw in....

Chill out. My mistake, there is indeed nothing wrong with your wiring configuration.

I assumed it was a typical two bank house system. It is the logical assumption as 80% of all boats are wired that way. In this case, he is talking about connecting a multi-battery house bank with multiple batteries, all of these need to go to the battery side of the shunt if they are not bonded together at the batteries. He discussed a bus bar connecting the positives but said nothing about the negative side.

I wanted to stress to him that he should also see the negative sides bonded together somewhere, if not at the batteries themselves, then at the shunt.

I'd be happy to delete the image if you like. I was trying to help this guy understand how shunts work. You might want to re-label your image for clarity (Engine Start) rather than the more ambiguous (Bank 2).

It brings up a good point though. I personally don't favor two bank house systems with A-B switches. What makes the most sense to me is a single large house bank, separate batteries for engine and if fitted, generator start, and a high amp cross connect for emergency use from the house bank to help start a flat starter battery. It would be helpful, if we saw a photo of his set up instead of trying to guess, given that he is unsure if he has a parallel or series connection. It is also unclear what type of batteries he is using.

[Maine Sail]

Originally Posted by Night_Sailor

Chill out. My mistake, there is indeed nothing wrong with your wiring configuration.

I assumed it was a typical two bank house system. It is the logical assumption as 80% of all boats are wired that way. In this case, he is talking about connecting a multi-battery house bank with multiple batteries, all of these need to go to the battery side of the shunt if they are not bonded together at the batteries. He discussed a bus bar connecting the positives but said nothing about the negative side.

I wanted to stress to him that he should also see the negative sides bonded together somewhere, if not at the batteries themselves, then at the shunt.

I'd be happy to delete the image if you like. I was trying to help this guy understand how shunts work. You might want to re-label your image for clarity (Engine Start) rather than the more ambiguous (Bank 2).

It brings up a good point though. I personally don't favor two bank house systems with A-B switches. What makes the most sense to me is a single large house bank, separate batteries for engine and if fitted, generator start, and a high amp cross connect for emergency use from the house bank to help start a flat starter battery. It would be helpful, if we saw a photo of his set up instead of trying to guess, given that he is unsure if he has a parallel or series connection. It is also unclear what type of batteries he is using.

I don't mind if one of my images is used, but I don't appreciate it when it is incorrectly iterpreted to make a point..

The term BANK designates separate battery BANKS, not individual batteries, though a single battery can also be considered a BANK.. As in BANK #1 and BANK #2. With only one shunt and two BANKS, the second bank goes on the loads side of the single house bank shunt. This is basic battery monitor wiring.

This is not a "two bank house systems" it is two individual banks one for reserve or emergency starting purposes and one for house/everything. The house bank is a larger single bank.

In this particular system the owner chooses to use the house bank for everything and the owner keeps bank #2 charged via an Echo Charger for reserve purposes. It could also be combined via a parallel switch as well..

If the negative of bank #2 is on the battery side of the house bank shunt counting errors will occur when the Echo is taking power from the house bank and not getting counted or when the switch is paralleled and current flows from one bank to the other... The type of battery in this system does not matter to the question GEL, AGM or FLA would all work identically.

In any two BANK configuration the second bank that is not being monitored by the house BANK shunt goes on the load side of the house bank shunt.

Parallel BANK



Series BANK

[simonpickard]

Hi,

I just checked again and they are in parallel. My boat was bought new in March but we've been onboard full time since then so I've dropped the amps from 330 down to 310. Does that sound about right?

Lastly, the 700 has a % option showing how full the battery is. Say it at 100% (fully charged) should I aim to recharge when this drops to 50% (which is what most people tell me is good for batteries)? Or does this display take that into account and it's a 100% to 0% when you need to charge?

Regards,
Simon

[UNCIVILIZED]

Simon,
Might some of the wiring in one, or several, of the systems be a bit old, & thus have a bit of corrosion. Enough to cause one or more of your meters to read lower than the actual voltage of the batteries? Or it could just be a case of some corrosion at the terminal(s) connections.
It never hurts to clean these... just break out the Dremel with the wire brush attachment :-) And also inspect any wire strands which you can see near the connector end fittings. Assuming you can see any that is.

Your best bet as to check your actual battery voltage is just to take a multimeter to the batteries, directly. Then you can see which of your hi-tech gauges is reading close to correctly, and decide on a plan of action from there.

Also, to get an idea of the true capacity of your batteries, charge them up fully. Then disconnect them from EVERYTHING, and let them cool off for a few hours in a no load state.
Once you do that, take a trusted multimeter & check their voltage, preferably a digital one. And compare your readings to a battery chart. That'll tell you what the true state of your batteries is, in terms of holding capacity, as it were. So that you can make a better guesstimate to use to enter into the system which is requesting how much capacity you have.

PS: Just in case, as an FYI info wise. I'm not sure what the ambient temperature is like where you are, but that also plays a good sized factor in what kind of readings you're getting from your batteries. And how much energy they'll hold.
Some of the more complex battery charts, as well as systems & meters will account for this, & others wont.
Also, how much energy any type of battery will hold varies from make to make, even within the same type(s) of batteries. So such plays a factor as well.
- And my apologies if this is old news to you, but I'm sure it's new info to many of the "younger" forumites.

[monte]

No Simon, set the Ah rating for the full rating of the batteries. The state of charge indicator is total charge so I never let mine below 60%. Note that this gets out of phase over time so don't rely on it for an accurate SOC. best to read the voltage for a more accurate indication.

http://modernsurvivalblog.com/wp-con...-of-charge.jpg

The state of charge is a calculation performed by the BM using amps out, amps in and peukerts law which allows for a loss coefficient. This coefficient is adjustable in the battery monitor settings but should be close enough for now. When you plug in at a marina, the batteries should fully charge and the BM should reset to 100%, but often if it's weeks between plugging in the monitor might calculate 100% when they are actually 80%.

The best time to check the voltage is after the batteries have been at rest with no charge in or out, so probably first thing in the morning.