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ezerini avatar image
ezerini asked

MPPT SmartSolar is charging from Load Output when alternator comes on

Hello!

I have a MPPT SmartSolar 100/20 charging a 24v LifePo4 battery. Connected to the Load is a DCDC Lead Acid charger for my vehicle battery. I made my first journey in the vehicle and found that the LifePo4 battery was being charged beyond the maximum i had set in the SmartSolar and apparently was being charged from current from the Load terminals. I switched off the DCDC Lead Acid Charger and it stopped charging the LifePo4.

I established that the alternator operated at 14v and the DCDC Lead Acid Charger was operating at 13.6v. Could it be that the DCDC was working in reverse when connected to a a higher voltage?

How can the SmartSolar use current from the Load Output to then charge the LifePo4 battery?

It was clear from my BMV that there was more current charging the LifePo4 battery than was being supplied by the solar panels and the only source generating power in the vehicle is the alternator. I confirmed this as the source by disconnecting the Lead Acid battery from the DCDC Charger and it stopped.

I was thinking of adding a Diode to the DCDC to prevent this, but I'm really confused that the SmartSolar and the DCDC were both working in reverse!

Any clues as to why this is happening and how to prevent it?

Thanks for any potential insights!


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3 Answers
wkirby avatar image
wkirby answered ·

It's difficult to comment on the DC-DC charger without knowingwhich one it is. It may be possible for a DC-DC charger to reverse feed depending on the topology and design of the circuit inside of it.

The Victron MPPT, yes, that can feed the battery from the Load Output terminals. This is because the Load Output is switched on to the battery bus inside. So anything connected to the Load Output it is effectively connected directly to the battery when the Load Output is activated.
Also, even if the Load Output of the MPPT is switched off, the battery can still be fed by a charging source on the Load Output because of the parasitic diode within the MOSFET switch.

If your DC-DC charger is of the type that can feed back, then a diode will be necessary between the MPPT Load Output and the DC-DC charger.

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ezerini avatar image
ezerini answered ·

Hi, thanks very much for the answer! Here's the Lead Acid Charger I am using:

https://www.aliexpress.com/snapshot/0.html?spm=a2g0s.9042647.6.2.7e144c4dctCnrl&orderId=8012758145438613&productId=4000156542513

I was actually thinking it could be quite useful for the DCDC to be reverse feeding since the alternator can be used to maintain the charge of my leisure battery, but I presume that the only way to control the max voltage in this scenario would be from DCDC, but this product has no settings. It's designed to work with input voltages from 8-36v, so perhaps if i'd left it connected, it may have charged to 36v or beyond.

If there is a more suited Victron lead acid charging product and also a recommended setup for my application, that would be great to hear about. I'm basically trying to ensure that the vehicle battery is always topped up.


Thanks again,

David.


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dejan avatar image
dejan answered ·

Hi David,

hope you don´t mind if i jump on the train. I am planing an identical setup:

- 100w solar panel on the roof fixed installation, an additional 120w foldable panel to be used in the future

- 100/20 Victron smart solar MPPT currently charging my 115Ah AGM traction leisure battery (location under the bonnet)

- 95Ah lead acid starter battery charged by the alternator

The plan is to help charge the leisure battery via Orion-Tr Smart 12/12 30A isolated DC/DC charger whilst the car is running, and on the other hand use the load output of the 100/20 mppt to charge the starter battery while the car is not running. The tricky part is, it should not drain the leisure battery whilst charging the starter battery and I´m not sure if there is a way to control the load output to allow only charging once a specified input from the solar panel has been reached.

I was thinking about 2 options on how to connect the starter battery to the MPPT and control or limit the voltage and current.

- use an Orion 12/12 9A - This would be the SMART solution, allowing the configuration/custumization (bluetooth dongle necessary) but I´m not sure if it can be configured to use it as I am planning to

- use a Batterie to Batterie Standby-Charger 12/12V, max. 3A from VOTRONIC - this would be the STANDARD solution allowing no configuration

The alternative would be a second Victron MPPT 75/15 for the 120W foldable panel to charger the starter battery with a manual switch to connect the solar panel in parallel with the 100W fixed panel to the Victron MPPT 100/20.

Comments and feedback would be appreciated

Dejan

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seedybne avatar image seedybne commented ·
Hi Dejan,


Did you solve this? I am aiming to set my vehicle up in a similar way.


I want to charge the deep cycle battery with solar during the day and allow it to top up the start battery when there is more solar energy available than the deep cycle needs.

At night, when driving, I want the start and deep cycle to link to keep the deep cycle topped up.

My set-up includes

SmartSolar (100/30) connected to the deep cycle.

BMV 712 connected to the deep cycle as the Main and monitoring start battery voltage as Aux.

A Cyrix combiner between the batteries.

Resettable breakers at each end - so I can achieve my objective by manually closing both breakers at night (when going camping and drawing from the deep cycle). During the day I can open a breaker if still driving or leave them closed when stopped and charging from solar.


Manually changing the breakers will achieve my desired outcome but I'd like the switching between solar and alternator to happen automagically to remove the possibility of forgetting to change them and either overcharging or flattening a battery.

I have have been thinking along the lines of using the SmartSolar Tx port and VE.Direct TX digital output cable to control a relay but haven't quite landed on a final configuration that I am confident will achieve my objective.


I am keen to hear how you set yours up in the end.


Thanks,

Chris


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kevgermany avatar image kevgermany ♦♦ seedybne commented ·

If you make the assumption that the starter battery does not need more than trickle charging from solar, the votronic unit is a good cheap automatic solution to keep the starter battery topped up. I've got one in my van. It's simply resistors/diodes, so charge current is very low and dependant on relative battery voltages.

If you combine it with the cyrix, you have an automatic system. When the engine is running, cyrix will connect the batteries, engine charges both. Close to 0 volts across the votronic, so no current through it. Engine not running, solar charging, starter will get a trickle charge. If house bank low, the starter gets close to nothing until the house bank voltage rises.

However if you have a smart alternator, don't use the battery combiner. Alternator can put out a high voltage which may damage your DC consumers. Rather use an Orion DC:DC charger.




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