Smart MPPT 75/15 showing very low battery voltage and disconnects load

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apeter asked Dec 27, '19

Smart MPPT 75/15 showing very low battery voltage and disconnects load

I have connected a 150w panel, SmartSolar MPPT 75/15 and a 120AH battery-feeding DC loads totalling to about 720WH. However, as of 3-4 days the load started to be disconnected. After viewing the trend on VictronConnect it shows 0w,21v and 0Amps for Solar, 13v and 0Amps for battery but it also shows my battery has been as low as 0.01v and high of 14.6v.

We have had cloudy weather with about 4 hours of clear skies/day. I am in East Africa so normally we have ups to 8 hours of sun on non-cloudy/rainy days. I have 2 different installations all acting up the same. Any ideas?

Thank you.

Alina

MPPT Controllers low battery warning

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Answer 1 · 2019-12-27T17:22:51Z

Matthias Lange - DE answered · Dec 27, 2019 at 05:22 PM

I guess the fuse is blown.

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Answer 2 · 2019-12-29T07:55:39Z

apeter answered · Dec 29, 2019 at 07:55 AM

Thank you. The fuse is blown. But what would cause both fuses on separate installations to blow almost simultaneously? Both installations have a 5w rechargeable battery and a 30w Motorola radio connected on the load port of the MPPT 75/15. Could it be overloaded? I am planning to replace the fuse but I would like to know so that I can prevent it from happening again?

Thank you again for your reply.

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Warwick Bruce Chapman commented · Jan 01, 2020 at 05:39 AM

I suspect peak power requirements of the radio during transmission is higher than 15A.

What are the specs?

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ttbb Warwick Bruce Chapman commented · Jan 01, 2020 at 07:30 AM

@apeter explain more about the loads

Does the radio have its own battery?

When you have a batteries / devices with batteries on the load output you have to consider if and when the main battery load output is cut due to low voltage then if there is still a drain on those batteries then there is going to be an additional load when the load output comes back on.

So, if the Motorola radio has its own battery and it could run with the main load output off for some time then when the load output comes back it is radio load + charing load.

Even with relatively small lithium batteries they can have a significant current draw when charging if nothing is limiting it.

If all else was good before and the loads were not overloading the load output then that would be my initial thinking.

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Answer 3 · 2020-01-01T11:36:36Z

apeter answered · Jan 01, 2020 at 11:36 AM

@warwick It's a DM3401-30W radio, so the max is 14.5A during transmission and 0.81A on standby. However, the radio is used only so often in a day.

@TTbb No, the radio doesn't have its own battery.

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