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Old 09-08-2018, 11:28   #1
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MPPT controller that senses actual battery voltage (w/o separate sense lead)?

I'm shopping for an MPPT controller that I can install as a drop-in replacement for an ancient/dumb pulse-type controller. The catch is that the controller is located a fair distance from the house bank that it is charging, so voltage drop between controller and batteries is a concern. Of course I'd prefer not to run any new/additional wires. So...

Is there such a thing as an MPPT charge controller that senses and regulates actual battery voltage during charging via the battery +/- charge wires (that is, without requiring a separate "sense" lead)?

Seems like this could be easily done if the controller periodically switched off the charging current to measure actual battery voltage, and then resumed charging, but with the voltage at the MPPT terminals adjusted/raised enough to more precisely achieve the desired voltage at the batteries. Or better yet, use the delta between the "idle" and "charging" voltages to determine resistance in the charging circuit and then use that resistance to calculate the voltage required at the MPPT terminals to bring the batteries to the exact targeted charging voltage.

This sounds pretty simple and obvious, so maybe they all do this? I'm under the impression though that they generally are regulating only the voltage at the MPPT bat+/bat- terminals, and the batteries always see a lower voltage. Is that right?

Thanks in advance,
Jeff
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Old 09-08-2018, 11:52   #2
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Re: MPPT controller that senses actual battery voltage (w/o separate sense lead)?

Look at Victron's SmartSolar series. They connect via bluetooth to a Smart-Battery-Sense which sends Bat-V and Bat-T to the solar controllers.
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Old 09-08-2018, 12:27   #3
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Re: MPPT controller that senses actual battery voltage (w/o separate sense lead)?

Jeff, why not put a Victron controller near the batteries and use either the dongle or usb widget to see what is going on.

Once set up it doesn't need any intervention.

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Old 09-08-2018, 14:14   #4
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Re: MPPT controller that senses actual battery voltage (w/o separate sense lead)?

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Pete: Jeff, why not put a Victron controller near the batteries and use either the dongle or usb widget to see what is going on.
That would surely be a better configuration, but it would require lots of rewiring, and I fear I'd damage the panels in the process. That's why I was looking for a controller I can drop-in to the existing location, but that's smart enough to determine actual battery voltage and compensate for voltage drop between controller and batteries.

To explain.. this is a cat, with 8x100w semi-flexible panels mounted on the hardtop above the cockpit. Panels are wired in parallel, with 16mm (~#6 AWG) running aft from panels to the controller in the port engine compartment. From there, 50mm (~#1 AWG) pos and negative run about 50ft via a roundabout path to the house batteries under the salon seat. To relocate the controller close to the batteries, I'd have to run all new wires from the panels the the salon. I'm not sure if that's doable without damaging the panels (pulling them up and reattaching them). And even if it is doable... I'm lazy, so would rather not if I can avoid it!


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LeaseOnLife: Look at Victron's SmartSolar series. They connect via bluetooth to a Smart-Battery-Sense which sends Bat-V and Bat-T to the solar controllers.
I really like this idea, but if I keep the existing controller location, the Smart-Battery-Sense and the MPPT controller would be about 25ft apart, with 4 cored bulkheads between them. Would the bluetooth connection reach that far?


Thank you both for the suggestions. I freely admit I'm looking for an easy way out, trying to improve on a less-than-optimal setup (from the factory) with the least amount of effort
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Old 09-08-2018, 14:23   #5
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Re: MPPT controller that senses actual battery voltage (w/o separate sense lead)?

Why not put a junction block where the controller was? Tie the #6 wires to the #1. Near the battery install the controller with the #1 cables as input and hook up new output wires to the batteries, no new runs.
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Old 09-08-2018, 14:40   #6
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Re: MPPT controller that senses actual battery voltage (w/o separate sense lead)?

Quote:
Originally Posted by Jetx View Post
...

I really like this idea, but if I keep the existing controller location, the Smart-Battery-Sense and the MPPT controller would be about 25ft apart, with 4 cored bulkheads between them. Would the bluetooth connection reach that far?
...

If distance is too far, you can extend the two leads of the Smart-Battery-Sense, with a pair of rather thin wires and run it closer to the MPPT controllers. But then temperature feedback from the Smart-Battery-Sense will not reflect real battery temp.



I just got the Smart Battery Sense added to my Victron MPPT controllers a few weeks ago, my distance is only 6 feet, but through several wood bulkheads, tool storage, etc. If I 'hide' the Smart-Battery-Sense behind a LeadAcidBattery, some controllers don't see it. So yes, distance and shielding is an issue.


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Old 10-08-2018, 08:27   #7
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Re: MPPT controller that senses actual battery voltage (w/o separate sense lead)?

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Why not put a junction block where the controller was? Tie the #6 wires to the #1. Near the battery install the controller with the #1 cables as input and hook up new output wires to the batteries, no new runs.
Thanks Paul... and good idea. Sadly, there's another quirk in the factory wiring that I didn't mention before. The #1 cables are routed from port engine compartment (where the solar controller is also located) to stbd engine compartment and then to house batteries. In both engine compartments, there's a "coupler" switch, allowing the house batteries to be connected directly to either/both start batteries for emergency purposes. So if I put PV voltage (direct from the panels) onto the #1 cables, then the engine batteries would see full panel voltage if either coupler switch is closed.

On the original question, I get the feeling that none of the established MPPT vendors (Victron, Morningstar, Outback, Midnite, Blue Sky etc) sell a controller that can determine actual battery voltage using only the battery +/- charging leads... so without an external sense lead, they're ALL going to regulate based solely on the voltage seen at the controller terminals while charging.

Does that sound about right?

Thanks.
Jeff
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Old 10-08-2018, 09:38   #8
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Re: MPPT controller that senses actual battery voltage (w/o separate sense lead)?

Jetx
I guess you could add a breaker at the junction box. This would protect the #6 wires when powered by the engine switched batteries and could be used to disconnect the panels in the rare case that you are switching the house to the engine. You'd just have to remember to switch both the batt switch and breaker to off.
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Old 10-08-2018, 10:11   #9
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MPPT controller that senses actual battery voltage (w/o separate sense lead)?

The voltage drop is .2 volts. Does that matter? The Victron has an app allowing you to set the voltages. You need the Bluetooth dongle. You can compare the battery voltage with the Victron measured voltage. Then you would know the voltage drop over the wire. Then lower the voltages for each charging stage to compensate for the voltage drop.
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Old 10-08-2018, 14:51   #10
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Re: MPPT controller that senses actual battery voltage (w/o separate sense lead)?

Quote:
Originally Posted by Jetx View Post
I'm shopping for an MPPT controller that I can install as a drop-in replacement for an ancient/dumb pulse-type controller. The catch is that the controller is located a fair distance from the house bank that it is charging, so voltage drop between controller and batteries is a concern. Of course I'd prefer not to run any new/additional wires. So...

Is there such a thing as an MPPT charge controller that senses and regulates actual battery voltage during charging via the battery +/- charge wires (that is, without requiring a separate "sense" lead)?

Seems like this could be easily done if the controller periodically switched off the charging current to measure actual battery voltage, and then resumed charging, but with the voltage at the MPPT terminals adjusted/raised enough to more precisely achieve the desired voltage at the batteries. Or better yet, use the delta between the "idle" and "charging" voltages to determine resistance in the charging circuit and then use that resistance to calculate the voltage required at the MPPT terminals to bring the batteries to the exact targeted charging voltage.

This sounds pretty simple and obvious, so maybe they all do this? I'm under the impression though that they generally are regulating only the voltage at the MPPT bat+/bat- terminals, and the batteries always see a lower voltage. Is that right?

Thanks in advance,
Jeff
Just about every solar charge controller on the planet has easily adjustable charge voltage setttings. Measure the voltage drop in the battery connection cable, add it to the battery manufacturer charge voltage values and set the controller values so that the controller can do exactly as it is designed to do.
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Old 10-08-2018, 15:03   #11
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Re: MPPT controller that senses actual battery voltage (w/o separate sense lead)?

According to ohms law the voltage change will be dependent on the current. So just putting in a fixed delta to compensate for a measured .2v drop isn't going to be that accurate over a range of charging currents.
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Old 10-08-2018, 15:26   #12
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Re: MPPT controller that senses actual battery voltage (w/o separate sense lead)?

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Originally Posted by macman4190 View Post
The voltage drop is .2 volts. Does that matter? The Victron has an app allowing you to set the voltages. You need the Bluetooth dongle. You can compare the battery voltage with the Victron measured voltage. Then you would know the voltage drop over the wire. Then lower the voltages for each charging stage to compensate for the voltage drop.
This is exactly what we do. The difference between what the Victron's on our boat measure and what the voltage is at the terminals is about .03-0.4V lower at the Victron. We adjusted the voltage using the Bluetooth dongle. Its not a big deal.
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Old 10-08-2018, 16:33   #13
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Re: MPPT controller that senses actual battery voltage (w/o separate sense lead)?

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Originally Posted by Jetx View Post
Thanks Paul... and good idea. Sadly, there's another quirk in the factory wiring that I didn't mention before. The #1 cables are routed from port engine compartment (where the solar controller is also located) to stbd engine compartment and then to house batteries. In both engine compartments, there's a "coupler" switch, allowing the house batteries to be connected directly to either/both start batteries for emergency purposes. So if I put PV voltage (direct from the panels) onto the #1 cables, then the engine batteries would see full panel voltage if either coupler switch is closed.

On the original question, I get the feeling that none of the established MPPT vendors (Victron, Morningstar, Outback, Midnite, Blue Sky etc) sell a controller that can determine actual battery voltage using only the battery +/- charging leads... so without an external sense lead, they're ALL going to regulate based solely on the voltage seen at the controller terminals while charging.

Does that sound about right?

Thanks.
Jeff
Suggestion.

1. Install Victron SmartSolar MPPT Controller in current location.
2. Install Victron 712 Battery Monitor Shunt at the Battery. With Monitor itself wherever you like nearby.

Configure both on wireless (bluetooth) VE.NET , the Battery monitor shares accurate voltage and temp with the Solar controller so don't need to use its own sense wires. (Can also be done on wired VE.Net).

Both devices have Bluetooth for control from your Phone.

Regards

Mark.
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Old 10-08-2018, 16:50   #14
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Re: MPPT controller that senses actual battery voltage (w/o separate sense lead)?

I think all or most of the current generation MPPT controllers have sense terminals. I have Morningstar 45 MPPT on the solar farm with battery sense and battery temperature probe.
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Old 10-08-2018, 16:59   #15
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Re: MPPT controller that senses actual battery voltage (w/o separate sense lead)?

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Originally Posted by travellerw View Post
This is exactly what we do. The difference between what the Victron's on our boat measure and what the voltage is at the terminals is about .03-0.4V lower at the Victron. We adjusted the voltage using the Bluetooth dongle. Its not a big deal.
It depends on the cause of the error. If it is a calibration error then the offset should work. If it is caused by wire and connection resistance then I don't see it working. If you have a .2v drop at 10amps then you'd have a .02v at 1amp.
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