question

t1-terry avatar image
t1-terry asked

Can a battery be interfaced between the solar and MPPT controller?

Can a smart 250/100 mppt controller be used between an open circuit 250vdc solar array and a lithium battery with a max voltage less than 250vdc, to charge a 48v lithium battery?

The reason I need such a set up is to utilise my DIY built EV for solar energy storage as well as back up storage when the sun doesn't shine .....

Our house is off grid but our workshop is still on the grid and we use the EV to drive the 5km from the house to the workshop and back home again. We plan to add solar to the workshop roof as well as the house so the EV battery can be charging while we are at work

Thank you in advance for any relies or advice that would guide me in a better direction if this idea wouldn't work ......


Terry

MPPT SmartSolar
1 comment
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Rob Duthie avatar image Rob Duthie commented ·

Hi

Not realy needs to be much lower of use the RS450 MPPT unit

as it is much higher input voltage of 450vDC

Now if you use the Victron solar configurator it will advise you want the configuation is for diffrent PV arrays are and the charge controller required limits etc. link below very usefull tool.

https://www.victronenergy.com/mppt-calculator

Regards

Rob D

NZ

1 Like 1 ·
4 Answers
johanndo avatar image
johanndo answered ·

You shouldn't use the EV / any battery as input into the MPPT controller. They are not made for this. Use a DC-DC charger or buck converter.

2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Mike Dorsett avatar image
Mike Dorsett answered ·

you would need to protect the input of the MPPT from over-current - both in scan mode, and in input protect mode. Also watch out for the MPPT overheating - as it will always go to max current. If possible externally control the MPPT in CC mode.

2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

t1-terry avatar image
t1-terry answered ·

DC to DC chargers for such work have a very short life it seems when you consider a DIY EV only gets driven for manybe an hr at a time, yet the DC to DC units are lucky to last 3 yrs.


The Smart MPPT soolar controllers are designed to handle more current than their max limit to cover that period of the day where the solar array produces more than the maximum controller output, so it just limits the input .....

I can understand the need for added fan cooling and I could add a thermostat and fans to force air across the back of of the controller, we have to do that now in some RV installations where the ambient temp goes over 40*C so the controller inside an enclosure in a closed up RV can get very warm ....

Terry

2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

t1-terry avatar image
t1-terry answered ·

OK, found this in the Victron 250/100 tech specs, PV short circuit current is 70 amps max, so I'd need some way of limiting the current draw from the 200v nom. battery to below 70 amps ..... a big choke maybe?

T1 Terry

2 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

johnny-brusevold avatar image johnny-brusevold commented ·

An interesting problem I tested some ideas about a couple of years ago.

A big choke I think will be far too unstable, and you have to burn a lot of energy.


I used a welding inverter of 300A with 180-240v ac input, but it worked just as well with 240V DC from 10x 24v tesla modules in series.

The idea was to make an off grid welder, which worked very well.


Also tested charging 24V lifepo4 with this at 150A continuously, then had to make some safety functions with gas-filled relays to avoid arcing, since OCV was about 90Volt. It was no more than a test, but it was "dangerous fun" but it worked.


I would go for one like this, possibly several in parallel, but you have to get control over the max amps drawn, since it is not designed for charging.

https://www.dwe-oss.eu/product/dc-dc-converter-250v-to-48v-1008w/

0 Likes 0 ·
johanndo avatar image johanndo commented ·
You know, it is 100A max on the output, so 5200W for a 52V or 2600W on a 24V system what means for 200V input 13A maximum current input for the 24V / 26A for the 52V.
0 Likes 0 ·

Related Resources

Additional resources still need to be added for this topic