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stonysolar avatar image
stonysolar asked

Mismatched Battery Voltages; MPPT 75/15 vs Storage

BattVoltage_AtBatts.jpgBattVoltage_ExCtrller.PNGPhantomLoadOutput_ExCtrller.PNGMPPT 75/15, VE.Direct Smart, 1 x 250W 24v Panel, 3 x 12v Gel Batteries

Although I've been running this set up for many years, I've only recently reverted to cross-checking outputs with a volt meter, as I've trusted the VE output figures. I have two questions for anyone interested in humouring me:

1. Why don't the voltages at VE Batt and Battery terminals match? Surely they're the same thing. Lately (possibly always!) I see a ~2.0v difference, with the VE 'output', and Bluetooth readout, being higher than the 'battery' voltage. Is this due to drop-off created by the attached inverter? I ask because I seem to be reaching 'Float' level rather quickly, and when the system goes nigh-nighs my VE voltage readout is dropping to sub-12v. Is this due to a 'tired' battery (sorry, a third question)?

2. Like many others, I have never attached a 'Load' to my system. Nevertheless, the VE readout often shows a 'phantom load'. Why is this? I haven't been able to find out why in any of the Victron literature.

Thanking You in Advance, SS


MPPT Controllersbattery charging
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2 Answers
klim8skeptic avatar image
klim8skeptic answered ·

Holy antiques Batman, an LD-200 :).

It would seem that you have some voltage drop between your mppt and batteries. Probably a bad connection, or a bad crimp.

While charging at a decent rate, use your multimeter and measure the voltage between the mppt + and bus +, then between the bus + and the battery +.

Do the same for the - side as above.

Take note of the voltage measurements (drop). Voltage drop is proportional to current. Small current / small voltage drop, large current / large voltage drop.




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stonysolar avatar image
stonysolar answered ·

Hi K8S, Thank you your suggestion. It was, in fact a slightly cruddy connection on the +ve side of the MPPT. I’ve rectified the problem and now await a couple of cycles to confirm success. MPPT and Battery voltages are now a close match. Cheers SS


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