Bluetti - Solar + alternator input into one port?

[thegoogler]

I purchased a Bluetti EB70S. Not my ideal power station but I couldn't find anything LFP that had 8A+ DC output options without needing to use the stupid cigarette lighter plug. The EB70S can take 8A @ 12-28V input to recharge. I'm running a 12V fridge and would like to maximize charging.

I can easily tie into a fuse block I installed which only operates when the truck is running. That will give me 100W input @ ~13.5V. Or I can use a 12-24V converter off that fuse block to get 200W (8@ * 24V). Both of these only work when the truck is running though, which is fine when I'm overlanding or heading to camp, but if I'm at camp a few days I don't want to run the engine for 4+ hours per day to recharge the unit.

I have enough space on the roof rack to add a 100W solar panel. I could swap inputs every time I plan to park the truck or drive it, but that's a PITA. I'm debating my options... I think one would be to buy a cheap PWM/MPPT controller with 24V output and simply join the two with a Y cable since the Bluetti won't pull more than 200W and so this will give me 100W when parked or 200W when driving (either via the alternator or a combination of solar + alternator, I think). But, can I just Y cable the solar panel and 12V or converted 24V from the alternator right to the input of the Bluetti and let it sort out the voltage (which will be somewhere between 12V and 24V?)

Are there other sensible options? I don't need to charge the starter battery and in fact I'd prefer to keep it separate.

 

[Dave in AZ]

I purchased a Bluetti EB70S. Not my ideal power station but I couldn't find anything LFP that had 8A+ DC output options without needing to use the stupid cigarette lighter plug. The EB70S can take 8A @ 12-28V input to recharge. I'm running a 12V fridge and would like to maximize charging.

I can easily tie into a fuse block I installed which only operates when the truck is running. That will give me 100W input @ ~13.5V. Or I can use a 12-24V converter off that fuse block to get 200W (8@ * 24V). Both of these only work when the truck is running though, which is fine when I'm overlanding or heading to camp, but if I'm at camp a few days I don't want to run the engine for 4+ hours per day to recharge the unit.

I have enough space on the roof rack to add a 100W solar panel. I could swap inputs every time I plan to park the truck or drive it, but that's a PITA. I'm debating my options... I think one would be to buy a cheap PWM/MPPT controller with 24V output and simply join the two with a Y cable since the Bluetti won't pull more than 200W and so this will give me 100W when parked or 200W when driving (either via the alternator or a combination of solar + alternator, I think). But, can I just Y cable the solar panel and 12V or converted 24V from the alternator right to the input of the Bluetti and let it sort out the voltage (which will be somewhere between 12V and 24V?)

Are there other sensible options? I don't need to charge the starter battery and in fact I'd prefer to keep it separate.

I read your post twice. I still can't really tell what your issue is. Can you more concisely state the proplem? I think it is that your Bluetti only has one charging input and you're trying to use solar AND a feed from car alternator in one input. But I'm not gonna go look at the specs for your station to see, much better for you to be clear so folks trying to answer don't have to do a ton of lookup to help...

Meh, I downloaded your usermanual.
There us a single input. 12 to 28v, 200W max, 8A max.
Used for a charge brick, or a solar panel, or a car port, the input is a 7909 port or 8mm commonly called.

At 12v, 8A is the max input. That is 96W. If you were trying to combine anything, you won't get more than the car port delivers anyways! In fact, not even, because car ports can deliver 120W at 12v, but your unit has a 8A max input OR 200W, if your input was 24.2v or so.

Buy a new, better, power station.

 

[thegoogler]

I read your post twice. I still can't really tell what your issue is. Can you more concisely state the proplem? I think it is that your Bluetti only has one charging input and you're trying to use solar AND a feed from car alternator in one input. But I'm not gonna go look at the specs for your station to see, much better for you to be clear so folks trying to answer don't have to do a ton of lookup to help...

Yes the Bluetti only has one input port. That port can accept anywhere from 12-28V. It will limit charging draw to 8A or 200W, whatever is less.

I would like to charge from the alternator and from solar, depending on the situation. I don’t want to just attach a 20V solar panel to the vehicle wiring of course.

What options do I have? What should I absolutely not do?

Things I have at my disposal or could buy:
1. My hands (to just manually change inputs)
2. An inexpensive Amazon 12-24 DC-DC converter (to boost alternator input from 100W @ 12V to 200W @ 24V (I have this)
3. A PWM or MPPT solar controller to change the variable solar output to 24V nominal
4. Various cables and wire and Anderson power pole connectors I can add.

 

[thegoogler]

One open question for me is “can I combine different voltages in any of these scenarios, or do the voltages all have to be identical?”

Another question is “if I use the 12-to-24 converter to step up the alternator voltage and I also connect the solar panel on the 24V side (so that both are charging the Bluetti) is there ever a scenario where I’ll feed voltage back to the vehicle and cause a problem? (I.e. if the Bluetti battery is full and the vehicle is running and the panel is getting sun will that voltage feed back to the 12V system or will the converter block it or step it back down?”

 

[Dave in AZ]

One open question for me is “can I combine different voltages in any of these scenarios, or do the voltages all have to be identical?”

Another question is “if I use the 12-to-24 converter to step up the alternator voltage and I also connect the solar panel on the 24V side (so that both are charging the Bluetti) is there ever a scenario where I’ll feed voltage back to the vehicle and cause a problem? (I.e. if the Bluetti battery is full and the vehicle is running and the panel is getting sun will that voltage feed back to the 12V system or will the converter block it or step it back down?”

You need a dc to dc charger which isolates your start battery from this unit, if you are going to mess with 24v on it. A converter doesn't isolate. There is a reason why people who want to alternator charge, buy a Redarc bcdc25, or a victron 12 12 30 dc to dc charger INSTEAD of a dc converter-- separation/isolation of your start battery and alternator from house system.
Since this is actually a power station, not a battery, and the input port doesn't ever output power, you probably could get away with using a converter here though. So, convert it up to EXACTLY, what your panels give, most good converters you can vary output. Then you might have alternator and solar voltage close enough that it wouldn't mess up the mppt input. Parallel, not series voltage input, test it before plugging into bluetti and frying it!

Normally, you can't really input multiple voltages into one port, because it is actually a solar charge controller mppt port, that is just ALSO being used to accept 12v input from car or 120v ac to dc charge brick. But if voltage varies, like solar panels, it seeks up and down for max power point, and will jack around up and down.

But thats a lot of coin for a converter and panel, needs to be 24 voc panel or less too, just for 200W. Just buy a better power station with TWO INPUTS, or 3, like the Pecron. Pecron 600 on sale now for $300, then you could just plug them all in at once...

 

[thegoogler]

Yeah my assumption on the input was 24V is fine and won’t feed back but I get your point there.

Ok so Im thinking one feasible option might be to get a cheap PWM solar controller, run the panel into the controller, and put the controller on the 12V side of the converter into the fuse box. It doesn’t guarantee isolation while the truck is running, but it does ensure I’m sticking with 12V into the system. The 12-24 converter can step up the solar plus alternator into the Bluetti from there… when the truck is running I’ll get 200W and when it’s not on then I’ll only get 100W max as expected.

Hmmm. Even with the Pecron the second input is 35+V so I’d still have to step that up, but yes dual input would simplify things. To be fair I hadn’t seen that as an option until now. Sadly I have the Bluetti already, though I bought it refurbished so it was only $300.

 

[thegoogler]

Ok so I guess my current question is: Are there any concerns with running the solar panel through a $20 PWM 12V solar controller and connecting it into the 12V side of the 12-to-24V DC-DC converter, keeping in mind that:

1. 12V side is isolated from the primary battery when the vehicle is off and connected when running, and
2. once the Bluetti is fully charged it will shut off and the PWM controller has nothing to charge (and I would hope would drop into open circuit mode)?

 

[Vigo]

There's nothing wrong with paralleling the solar and 12v from the truck together as far as hurting anything.. the solar panel has diodes and will not act as a 'drain' on the truck just because they are hooked together. So it's perfectly SAFE.

The issue will be whether it's effective. If your solar panel is putting out something like 17v and your 12v system something like 13.X volts, the MPPT in the Bluetti MIGHT not find the 'true' max power point of the combined sources because it will have to pull the circuit down below 13v to find that true max. If the Vpmax (voltage at which max power is made) of the solar panel is something like 15v, the Bluetti might pull the circuit down to 14v, see the total power dropping, and go back up to 15v and settle there without ever knowing that there was actually another 100w available if it pulled it down below 13. So if that scenario came true your 100w from the 12v system would not be utilized. So it basically depends on how the MPPT tracking works in the bluetti, whether combining those sources will truly give you 200w or not.

I can see a way to use a PWM controller here but unless you boost the voltage up into the 20s you will never get more than ~100w of charging so it doesnt inherently address that issue. But if you powered the Bluetti input from the load ports of a PWM controller you would gain item #1 from your list above just by setting the load ports not to activate until say 12.8v or so, that way the Bluetti cannot drain your starter battery when the truck isn't running.

 

[thegoogler]

I can see a way to use a PWM controller here but unless you boost the voltage up into the 20s you will never get more than ~100w of charging so it doesnt inherently address that issue. But if you powered the Bluetti input from the load ports of a PWM controller you would gain item #1 from your list above just by setting the load ports not to activate until say 12.8v or so, that way the Bluetti cannot drain your starter battery when the truck isn't running.

At the moment I’m thinking about the PWM controller sitting behind the 12-24 converter. So from the Bluetti perspective it’s all 24V power. If all I have is solar then it’s 100W max regardless. If I’m driving in a tunnel then I only have 200W of alternator.

If the engine is running then it’s some combination of the two… but the alternator will put out 13.5-14V, so the PWM controller may or may not activate if it thinks the battery is charged. If the PWM controller lets me configure it to set that 13.2V is a full battery then it shouldn’t ever activate when the engine is on, so I should either get 100W or 200W depending on whether the truck is off or on. If the PWM controller can’t set the battery full level then voltage will fluctuate between 13.5V and 14.6V depending on whether solar is active or not but if the engine is running it should always be 200W.

Another option if the engine is running might be for me to use an NC relay and have it open (disconnect) when the engine starts. That’s slightly more complicated than I’d like though.

 

[Vigo]

Ok, sounds like your idea works. I had forgotten about the 8a limit as i typed most of my last post anyway, because even if the Bluetti knew to pull the circuit down to <13v, it would still only be 100w at that point, so a whole paragraph was sort of wasted there..

If you're talking about hooking the solar up through a 12-24v step up converter, make sure the converter can handle the VOC of the panel on its input.

If you want to spend ~$50 there are 'boost mppts' which would seek mppt of the panel AND boost output voltage up to ~20-something (settable on some models i looked at), but thats probably about twice the money you would spend just to get a basic 12-24v 200+w step up converter with no mppt shenanigans going on.

 

[justinm001]

I would run a 12-24v DC DC converter for alt and a mppt for the solar and program them both to output 24-27v.

Something like this for the alternator side.

Amazon.com

Wire them up using that same 8mm plug then get a Y combiner cable.

Amazon.com

This way either or both can plug in. Whichever has the higher voltage will be the primary. Add a couple inline to fuses before the 8mm

 

[thegoogler]

Ok, sounds like your idea works. I had forgotten about the 8a limit as i typed most of my last post anyway, because even if the Bluetti knew to pull the circuit down to <13v, it would still only be 100w at that point, so a whole paragraph was sort of wasted there..

If you're talking about hooking the solar up through a 12-24v step up converter, make sure the converter can handle the VOC of the panel on its input.

If you want to spend ~$50 there are 'boost mppts' which would seek mppt of the panel AND boost output voltage up to ~20-something (settable on some models i looked at), but thats probably about twice the money you would spend just to get a basic 12-24v 200+w step up converter with no mppt shenanigans going on.

I think it’ll work but confirmation (or calling me nuts) is why I’m here ;-)

If I put a PWM controller between the solar panel and the 12v side then the converter should be ok since it wouldn’t see anything higher than the 14.5V coming from the alternator anyway. But I’ll double check to make sure the extra voltage doesn’t fry it

 

[thegoogler]

I would run a 12-24v DC DC converter for alt and a mppt for the solar and program them both to output 24-27v.

Something like this for the alternator side.

Amazon.com

Wire them up using that same 8mm plug then get a Y combiner cable.

Amazon.com

This way either or both can plug in. Whichever has the higher voltage will be the primary. Add a couple inline to fuses before the 8mm

Yeah that converter is what I have just a 20A version. And the cable is what I was thinking about using (or Anderson PP wires). So really just confirming if I did that I wouldn’t F something up since the converter would output 24V while the panel was likely a bit higher… and also that the panel wouldn’t backfeed through the converter and send 24V into the truck. That is why I started thinking about using a PWM solar charge controller to produce 12V but trying that to the low side of the converter. That isn’t isolated when the truck is running but should otherwise work. I could go MPPT instead of PWM but the latter are cheap and the difference in efficiency isn’t meaningful for my use case… the only necessary function I think is an adjustable battery voltage setting

 

[justinm001]

Yeah that converter is what I have just a 20A version. And the cable is what I was thinking about using (or Anderson PP wires). So really just confirming if I did that I wouldn’t F something up since the converter would output 24V while the panel was likely a bit higher… and also that the panel wouldn’t backfeed through the converter and send 24V into the truck. That is why I started thinking about using a PWM solar charge controller to produce 12V but trying that to the low side of the converter. That isn’t isolated when the truck is running but should otherwise work. I could go MPPT instead of PWM but the latter are cheap and the difference in efficiency isn’t meaningful for my use case… the only necessary function I think is an adjustable battery voltage setting

No the 12/24 DC converter will block power from back feeding into the 12v

 

[ejfluhr]

You could go simple-safe with a 1-2-Off switch. There are cheaper random-brand options if cost concern is higher versus:

Blue Sea Systems 6008200 m-Series Series Battery Switch 3 Position Selector, Black https://a.co/d/egzUYZK

Or you could go more automated with a DC 2-way relay controlled by your ignition switch. Default to solar panel when off, change to vehicle when ignition is on (presumably car is then running).

Since this approach decouples the inputs, you don't need a PWM and can leverage the MPPT in the Bluetti. Also you can run a 12v->24v converter (or not) on the vehicle side.