Charging a Power station with an Existing Battery Bank via DC?

CompMan2020

Solar Enthusiast
Trying to figure out how to use my solar system to charge my current AGM battery bank and a Bluetti EB240 at the same time. I don’t want to use the inverter either, I’m sure that’s the easiest way but I rather use DC for efficiency. I tried doing a search here first but came up with nada. Any Thoughts?
 

snoobler

Solar Honey Badger
Moderator
Depending on the efficiency of your inverter, you may only be losing 6-10%. Is that something you can't tolerate, i.e., your current system can't afford the loss?
 

CompMan2020

Solar Enthusiast
Depending on the efficiency of your inverter, you may only be losing 6-10%. Is that something you can't tolerate, i.e., your current system can't afford the loss?

Just thinking DC is better all around. Less stress on the inverter, a bit more life on the battery bank, Less heat generated by not having the Inverter running all day long in a hot van parked in FL and I'm sure there are other advantages that doesn't come to mind right now.
 

snoobler

Solar Honey Badger
Moderator
Context is everything. That makes a lot more sense.

from:


Is there only one port for both solar panel charging and AC charging?

It looks like the AC adapter outputs 42VDC/200W (4.8A) - verify this on the AC adapter output if you can.
The PV can accept a 16-60VDC/500W source up to 10A

Sounds like all you need to do is to get a DC-DC converter to up the voltage and plug it in the hole.

Assuming your battery is 12V, you would get a 12-48VDC converter that puts out up to 10A:

This would work:


This would give you almost the same amount of charging as the AC adapter.

The panels would charge your battery and your battery would feed your Bluetti. If the batteries in float, the panel keeps pushing power to the bluetti, so as long as you have more than 192W coming in from the panels, you're not using the battery.

another lower power option would be a 12-24/5A (120W):

 

CompMan2020

Solar Enthusiast
Context is everything. That makes a lot more sense.

from:


Is there only one port for both solar panel charging and AC charging?

It looks like the AC adapter outputs 42VDC/200W (4.8A) - verify this on the AC adapter output if you can.
The PV can accept a 16-60VDC/500W source up to 10A

Sounds like all you need to do is to get a DC-DC converter to up the voltage and plug it in the hole.

Assuming your battery is 12V, you would get a 12-48VDC converter that puts out up to 10A:

This would work:


This would give you almost the same amount of charging as the AC adapter.

The panels would charge your battery and your battery would feed your Bluetti. If the batteries in float, the panel keeps pushing power to the bluetti, so as long as you have more than 192W coming in from the panels, you're not using the battery.

another lower power option would be a 12-24/5A (120W):


Yes this! You Rock! Exactly what I was looking for. Thanks!
 

snoobler

Solar Honey Badger
Moderator
You're welcome. Just triple and quadruple check your polarity on the plug you fashion... :)
 
Last edited:

CompMan2020

Solar Enthusiast
Context is everything. That makes a lot more sense.

from:


Is there only one port for both solar panel charging and AC charging?

It looks like the AC adapter outputs 42VDC/200W (4.8A) - verify this on the AC adapter output if you can.
The PV can accept a 16-60VDC/500W source up to 10A

Sounds like all you need to do is to get a DC-DC converter to up the voltage and plug it in the hole.

Assuming your battery is 12V, you would get a 12-48VDC converter that puts out up to 10A:

This would work:


This would give you almost the same amount of charging as the AC adapter.

The panels would charge your battery and your battery would feed your Bluetti. If the batteries in float, the panel keeps pushing power to the bluetti, so as long as you have more than 192W coming in from the panels, you're not using the battery.

another lower power option would be a 12-24/5A (120W):



Just an update -

I got the EB240 in today and immediately started testing...

Using the 48V/4A DC to DC Converter I was getting over 300 watts charging on the EB240 which is great, but it was getting super hot. I immediately halted all testing and ran out to Home Depot to get a Infrared Thermometer and a Clamp on Amperage Meter.

When I got back I ran the same test and saw that the converter was putting out 48V at 8A and the temperature on the enclosure reached 200 Fahrenheit rather quickly. It didn't shut itself down so its safe to say I got a defective unit which will be sent back tomorrow.

Luckily for kicks and giggles I ordered a second unit with a higher wattage output since the EB240 can accept up to 500 watts for charging.
I was looking for a 48V/10A unit, but settled on a 24V/10A which is working just fine. I'm getting 220 watts charging on the EB240 which is the same output I get with the AC Charger and temps didn't get any higher than 150 degrees with my limited testing. Happy Camper so far. Need to see how it performs long term.

Thanks again for steering me in the right direction!

On another note.... I need to see why I'm only getting around 0.250KW of power a day from my 200W solar panels. Luckily I have 200 more coming tomorrow, but it seems a bit low to me. Hopefully I can figure out how to get more power from my panels.
 

snoobler

Solar Honey Badger
Moderator
I linked ones with lower wattage in order to keep it under the 200W limit. Heat is always a factor with those little buggers, and that heat is lost efficiency.

Shading and heat are your two likely candidates. Shading part of a panel can dramatically impact its output. If the back of the panel is getting radiant heat from the roof and raising its temperature significantly, that could be a problem.

Check the charge controller settings.

Check for loose connections through the entire system.

Could you be very miserly and only need .25kWh/day?
 

CompMan2020

Solar Enthusiast
I linked ones with lower wattage in order to keep it under the 200W limit. Heat is always a factor with those little buggers, and that heat is lost efficiency.

Shading and heat are your two likely candidates. Shading part of a panel can dramatically impact its output. If the back of the panel is getting radiant heat from the roof and raising its temperature significantly, that could be a problem.

Check the charge controller settings.

Check for loose connections through the entire system.

Could you be very miserly and only need .25kWh/day?

Maybe, I haven’t been using the van lately since I took it apart to add some stuff. Now that I have the Bluetti I can bypass the battery bank and connect straight to the solar panels to see if there’s a major difference.

I’ll post some pics so that you guys can see what I’m working with.
 

snoobler

Solar Honey Badger
Moderator
If you can check your charge controller and see that it's hitting bulk/absorption voltages, .25kWh is all you need.
 

CompMan2020

Solar Enthusiast
If you can check your charge controller and see that it's hitting bulk/absorption voltages, .25kWh is all you need.

You were right!

Since my batteries were topped off the mppt scaled back the charging. Yesterday I drained them down a bit messing with the Solar gen and today at around 11:30am I was at .55kwh for the day and the batteries were topped off.

I Just hooked up the EB240 to the system and left it to charge. It was at around 60%, so it would need about 1000wh to top off. The Van is in my driveway and its sloped downward a bit facing west. I get the best sun in the afternoon so It should get close to a full charge by the end of the day. At least I'm hoping it would.

Here are some pics of my setup. Its a bit messy since I'm still working on the add-ons.
 

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snoobler

Solar Honey Badger
Moderator
Good confirmation.

Those racks may have a substantial impact on panel output.



Based on the PV readout, I would guess you have them in parallel, which would ensure at least one panel is unaffected by the shading of the other.

Glad you were able to get where you wanted with the converter.
 

CompMan2020

Solar Enthusiast
Good confirmation.

Those racks may have a substantial impact on panel output.



Based on the PV readout, I would guess you have them in parallel, which would ensure at least one panel is unaffected by the shading of the other.

Glad you were able to get where you wanted with the converter.

Yes agreed!

I first intended to mount them on top of the racks but they were too small. I wouldn't have liked it on top anyway since the racks sit high. I did not enjoy drilling more holes on the roof to bolt them on either. I'll have to live with the shading for now since the racks are holding up my awning.

I'm looking into the flush mount brackets for the Awning so that I can maybe sell or repurpose the racks.

All a result from doing my homework after the fact! :p

Thanks Again!
 

snoobler

Solar Honey Badger
Moderator
Story of my life. I'm buying a $900 SCC to replace my $700 SCC because I did homework after... :(
 

zilch0md

New Member
Just an update -

I got the EB240 in today and immediately started testing...
[snip]
... but settled on a 24V/10A which is working just fine. I'm getting 220 watts charging on the EB240 which is the same output I get with the AC Charger and temps didn't get any higher than 150 degrees with my limited testing. Happy Camper so far. Need to see how it performs long term.
[snip]

Hi CompMan2020,

I was about to post a new thread, when the server listed this thread as being related to the title I had in mind...

Unaware of your experiments, I've recently started using what I suspect is the same DC-to-DC convertor you are using, rated for 12V input and 24V output at 10A (240W), the equivalent of pulling 20A at 12V:


You've made no mention of any difficulties getting the 24V output of the convertor connected to your Bluetti EB240, but I had to jump through a lot of hoops to get around the fact that the EB240 expects to see "+" polarity at both the inner sleeve of the 7.9mm power plug and at the center pin. Most cables that can be purchased with a 7.9mm plug already attached at one end have an unpowered center pin. That's the case with this iGreely cable, for example.

https://www.amazon.com/gp/product/B07WP4696G/

This can be confirmed by testing continuity between the inner sleeve of the unenergized 7.9mm plug of the Bluetti AC charger and the center pin. Those two poles of the three-pole plug are electrically connected within the cable. Try checking that continuity with your choice of several aftermarket cables that come with a 7.9mm plug and you'll find no continuity between the inner sleeve and the center pin. Indeed, there are several such cables at Amazon, made for various purposes other than use with the EB240, where reviewers are complaining that the center pin is not engergized.

This requirement that the centerpin and the inner sleeve both soldered for "+" prevents use of a Jackery cable with the Bluetti EB240, for example.

I could only find one one solderable 7.9mm plug online. Note within the data sheet PDF, that it has 3 poles (center pin, inner sleeve and outer sleeve):



Can you please tell me how you built the cable that goes from your DC-to-DC convertor to the Bluetti EB240's 7.9mm charging jack?

I probably overcame the problem the hard way, but I did get it working:

Zilch0md_EB240_Charging_from_12V_source_via_DC-to-DC_convertor.jpeg

With a 3-liter V6 at idle, it loses some RPM when the alternator kicks in under the 20-Amp load - which, by the way, is too great a load for the 15A fuses and, most likely, 14AWG wire that feeds the 12V accessory jacks inside my vehicle.

Input voltage to the 12V-to-24V 10A convertor drops from 14.1 to 11.0, when the 7.9mm plug is inserted into the EB240's charging jack. (Output voltage drops from 24.0 to 23.8.)

I'm using 12AWG cables for the entire circuit, with clamps on the battery posts and a 35A inline blade fuse, near the battery. In addition to the convertor itself and the two voltmeters, the project box contains a 40x40x20mm 0.03A 12V fan that pumps air into the box, across the heat sink fins and out through holes drilled in the opposite side. It never gets above ambient temperatures, that I can tell by handling the box.

https://www.amazon.com/gp/product/B07V4GGPW3/
 

CompMan2020

Solar Enthusiast
Hi CompMan2020,

I was about to post a new thread, when the server listed this thread as being related to the title I had in mind...

Unaware of your experiments, I've recently started using what I suspect is the same DC-to-DC convertor you are using, rated for 12V input and 24V output at 10A (240W), the equivalent of pulling 20A at 12V:


You've made no mention of any difficulties getting the 24V output of the convertor connected to your Bluetti EB240, but I had to jump through a lot of hoops to get around the fact that the EB240 expects to see "+" polarity at both the inner sleeve of the 7.9mm power plug and at the center pin. Most cables that can be purchased with a 7.9mm plug already attached at one end have an unpowered center pin. That's the case with this iGreely cable, for example.

https://www.amazon.com/gp/product/B07WP4696G/

This can be confirmed by testing continuity between the inner sleeve of the unenergized 7.9mm plug of the Bluetti AC charger and the center pin. Those two poles of the three-pole plug are electrically connected within the cable. Try checking that continuity with your choice of several aftermarket cables that come with a 7.9mm plug and you'll find no continuity between the inner sleeve and the center pin. Indeed, there are several such cables at Amazon, made for various purposes other than use with the EB240, where reviewers are complaining that the center pin is not engergized.

This requirement that the centerpin and the inner sleeve both soldered for "+" prevents use of a Jackery cable with the Bluetti EB240, for example.

I could only find one one solderable 7.9mm plug online. Note within the data sheet PDF, that it has 3 poles (center pin, inner sleeve and outer sleeve):



Can you please tell me how you built the cable that goes from your DC-to-DC convertor to the Bluetti EB240's 7.9mm charging jack?

I probably overcame the problem the hard way, but I did get it working:

View attachment 27625

With a 3-liter V6 at idle, it loses some RPM when the alternator kicks in under the 20-Amp load - which, by the way, is too great a load for the 15A fuses and, most likely, 14AWG wire that feeds the 12V accessory jacks inside my vehicle.

Input voltage to the 12V-to-24V 10A convertor drops from 14.1 to 11.0, when the 7.9mm plug is inserted into the EB240's charging jack. (Output voltage drops from 24.0 to 23.8.)

I'm using 12AWG cables for the entire circuit, with clamps on the battery posts and a 35A inline blade fuse, near the battery. In addition to the convertor itself and the two voltmeters, the project box contains a 40x40x20mm 0.03A 12V fan that pumps air into the box, across the heat sink fins and out through holes drilled in the opposite side. It never gets above ambient temperatures, that I can tell by handling the box.

https://www.amazon.com/gp/product/B07V4GGPW3/
I just cut off the MC4 connectors on the cable that came with the Bluetti. Then using a multimeter I confirmed the positive and negative of the cable then soldered on a XT60 plug on the wire and onto DC to DC converter. Was pretty easy.

tempImagetLD2zJ.png
 

zilch0md

New Member
Thanks! You took a very fortuitous shortcut (pun intended), having retained the proprietary soldering at the 7.9mm plug of that Blueitti cable. 😋 Nice going!
 
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