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Battery Monitor with shutdown relay.


Chris Hobson
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I spent last night checking on the net and I see Victron have a battery monitor with relay which you can invert (60V 1A). Now the quest is to find a a contactor that will work @ 60V 1A. My plan is to have a contactor on the AC load that will cut out if the DOD exceeds 30%. I am a farmer and employees are not going to worry about the nuances of a solar system and I want to prevent disaster in my absence. Rather switch off than have my investment ruined.

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Hi Chris,

 

No need for a 60V contactor.

Use a normal 220V contactor that is correctly sized for your load.

Use an extra circuit from your invertor output and wire it through the Victron battery monitor to power the contactor.

This way you can drop certain loads when the battries is running low.

Other loads like lights can stull run untill the invertor shuts down by itself due to the "low DC cutoff" setting.

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The correct way to "calculate" DOD will be with something like the Victron battery monitor.

It is programmed with your battery parameters and measures the amps flowing in and out of the battery bank to detirmine DOD.

 

By using just the voltage to calculate the DOD is a very rough estimation, but generally 11.75V is seen as 30% DOD.

Thing is, current drawn from the battery also affects the volts, so the same battery at 2 diffrent currents, will give you diffrent voltages. Now which voltage gives you the correct DOD???

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Hi Superdiy

 

I may have missed something. The Axpert maximum cut-off is 48V which is roughly between 50% and 40% DOD according to what I have found on the net so the inverter is unable to hit the sweet spot in terms of shutdown so that your batteries last. You can switch to grid and start charging at DOD of about 30% but in my instance since I do not want the generator on auto start and I am off-grid this is not an option.

 

Wetkit thank-you I don't have the Victron battery monitor in front of me but it seems it only has relay output. My supplier says the contactor is no problem. I suspect 60V 1A is enough to pull in the contactor's coil and that they will supply me with a 240V SP contactor.

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Hi Superdiy

 

I may have missed something. The Axpert maximum cut-off is 48V which is roughly between 50% and 40% DOD according to what I have found on the net so the inverter is unable to hit the sweet spot in terms of shutdown so that your batteries last. You can switch to grid and start charging at DOD of about 30% but in my instance since I do not want the generator on auto start and I am off-grid this is not an option.

 

Wetkit thank-you I don't have the Victron battery monitor in front of me but it seems it only has relay output. My supplier says the contactor is no problem. I suspect 60V 1A is enough to pull in the contactor's coil and that they will supply me with a 240V SP contactor.

 

OK, seems that I misunderstood you.  I thought you want to shutdown the inverter (output) when you reach a certain preset level, but reading your initial post again it seems that you want to control a relay at a certain level and I think what you want to achieve by that is to disconnect certain circuits with the relay, am I understanding it correctly now? 

 

OK, so why don't you use the on-board relay (Dry Contact Signal, page 10 in the manual) for that purpose?  Since the relay can only handle 3A, you might want to use it to switch a standard contactor (or relay with 220V coil) which in turn can switch anything on or off (depending on the contact rating of the contactor).  Then you don't have to buy a separate battery monitor/cut-off device.

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This is what I love about this forum. You have others helping you get to your goals. I have re-read page 10 and yes I can get it to work (I think).

 

I plan to run the inverter in utility first mode (strange since I am off grid, but bare with me). During the day the generator will be off and we will use mostly solar and perhaps a bit of battery on cloudy days or high demand. In the evening the generator will go on and supply my employees with electricity. I might as well make use of this electricity to top up batteries and for the AC load of the farmhouse. I am hoping that by 9.00 pm when the generator goes off, my batteries are either fully charged or nearly so. I should have very little draw overnight  just a solar compatible fridge and deep freeze and maybe 1 or 2 LED beside lights for an hour or two. I  only have 48V 260Ah battery bank so need to be careful with what power I draw from it if I do not want it depleted halfway through the night.

 

The utility first mode does have a low DC warning but does not say at what voltage it is. May be the manual is badly worded and you can set it in Program 12 like SBU mode. I will have to experiment.

 

Thank-you for making me re-read the manual. From past experience reading manuals I know I am not always fluent in Chinese English.

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