Hi there,
I hope this is not redundant. It is very similar to https://forum.allaboutcircuits.com/...ile-supplying-power-to-my-device.67530/page-2

I have a ecoflow battery with a max dc output of 8A. I would like to be able to draw 12A. I can’t modify the ecoflow battery (it’s a portable power supply that is user friendly, but not editable). If I get a 30Ah lithium battery and set it up so my device pulls its 12 amps (just for a few minutes, then it calms down to a few amps) can I make it such that my ecoflow charges the new 30Ah battery? If they are all connected and the 30Ah battery sees a 12amp draw, will this just be passed onto the ecoflow, demanding 12amps from it and blowing its 8amp fuse?

i hope this makes sense. It’s very similar to the figure drawn by @Tonyr1084 in post #14 of the thread I cited. It’s just that the power supply is a second battery only capable of supplying 8A

thanks in advance!

sam

 

It largely depends upon the relative voltage of the two batteries (what is their voltage?).
If they are basically the same, then the 8A battery will provide very little charge to the other battery.

How is the ecoflow battery charged?

It would likely be easier just to buy a charger for the Lithium battery and not use the ecoflow.

Otherwise, to avoid blowing the 8A fuse, you would likely need an 8A current limit circuit at the ecoflow battery output.
A simple version of that requires just a power MOSFET, a BJ transistor. and a couple resistors.

 

You didn't mention any Voltages, or how long You want to pull ~12-Amps.

Generally, charging a Battery with another Battery, is just a waste of Power.
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Thanks for the responses!

The 12amp pull is just for 3 minutes, then drops to about half an amp for as long as I want and then 12 amps again for 3 minutes. It’s for a glow plug in a heater.

Both batteries are “12 volts” but the output for the 8A plug is 13.6v. I would assume any lifepo4 battery I buy would be similar?

I guess why I wanted to use the ecoflow is because I can easily charge it from my car, solar or ac. It is ~100Ah and is paid for. I just need a way to get 12amps for a few minutes and thought a second battery that I wired myself could provide that brief burst in power, but that I could then depend on my larger battery for the perhaps 10 hours that I would draw .5amps (total 5Ah). At the end of that 10 hour period I need to pull 12 amps again though.

perhaps I should just use the 30Ah battery by itself and then when not in use charge it from the 100Ah one? I wanted to keep it simple and not try to set up a parallel way to charge the 30Ah battery from solar and my car.

 

How about disconnecting the two batteries when operating the glow-plug, then allow the EcoFlow to charge the other one the rest of the time?

 

Thanks for the responses. The 12amp pull is just for 3 minutes, then drops to about half an amp for as long as I want and then 12 amps again for 3 minutes. It’s for a glow plug in a heater.

Both batteries are “12 volts” but the output for the 8A plug is 13

How about disconnecting the two batteries when operating the glow-plug, then allow the EcoFlow to charge the other one the rest of the time?

Definitely crossed my mind. I was hoping for something more elegant, but perhaps I should just keep it simple…

 

Thanks for the responses. The 12amp pull is just for 3 minutes, then drops to about half an amp for as long as I want and then 12 amps again for 3 minutes. It’s for a glow plug in a heater.

Both batteries are “12 volts” but the output for the 8A plug is 13


Definitely crossed my mind. I was hoping for something more elegant, but perhaps I should just keep it simple…

On second thoughts - I wonder if connecting the second battery across the first after it has been partially discharged will also take enough current to blow the fuse.

 

I suspect trying to charge one battery from the other is problematic, and won't provide much charging.

What is the make and model of the ecoflow supply?

 

Maybe it's me but I'm not getting a clear picture. Joeyschmoey Do you know how batteries are rated? An 8Ah battery is rated to deliver 8 amps for one hour or 1 amp for 8 hours. Or any combination there in-between. Batteries are also rated for their max current capabilities, not often stated on small batteries. An automobile battery may be rated for (and I'm just throwing numbers out there) may be rated for 30Ah but be capable of 450 cold cranking amps. That means the battery can deliver 450 amps max at any given moment. It all depends on the load. Ohms law applies to how many amps a glow plug will draw. While I don't know much about glow plugs, I'm assuming they are similar to a light bulb. They heat up and glow. When they're cold they have very low resistance but when they get hot the resistance goes way up which is why it draws much less power once warmed up.

Are you working on a diesel engine? Are you using a glow plug from a diesel engine for some other project? Car batteries are nominally referred to as 12 volts. A fully charged and fresh 12 volt battery will have 12.6 resting volts. When the vehicle is started the charging system will restore the charge that was used for starting the vehicle. It's not uncommon to see voltages go up to 14.5 volts, but after the battery has taken a major portion of the power it needs for recharging then the auto electric system runs at 13.6 to 13.8 volts while the engine is running. That's also the float charge for a car battery.

If you can give us a schematic of what you're trying to do and give us some more detailed information about the battery(ies) then we can probably zero in on an answer that will better suit your project.

Also, could you link the original thread so I can look back at what I drew for someone else?

 

Hi all, Sorry for the late response.

The eco flow is a delta 1300 model. I would be using the cigarette lighter port on it, which provides the 13.6v, 8A.
https://us.ecoflow.com/products/delta-portable-power-station

I am trying to run a diesel heater, the glow plug is built into the heater. It only draws 12 amps for a few minutes, while heating the glow plug, then burns diesel for heat and only uses .5A for running a fan. When I shut it down the glow plug comes on for a few minutes again.

Here is the link to the other thread, just for the schematic: https://forum.allaboutcircuits.com/...ile-supplying-power-to-my-device.67530/page-2
but I also drew the schematic of what I want below.

Basically, I already own a big battery, but need to increase the amperage I can get out for a brief period. The "30Ah" battery is just a place holder. I don't know the specifics of it, I chose 30Ah, because that should handle one evening of using the diesel heater (12A for 5 min + 10hrs of .5A + 12A for 5min = 1Ah + 5Ah + 1Ah = 7Ah + a lot of wiggle room). I think the wiring in yellow/purple/green below would work and be independent. I just want to know if I can charge my new (30Ah) battery from my existing one. If I connect them so the 10hours of .5A is drawn from the ecoflow, when the heater demands 12A, will that be pulled equally from both batteries?

I have already setup a way to charge the ecoflow from solar and my alternator, so ideally, I could just have that make and store power, and then pass it off to the new battery that has the amperage to run the heater.

Hope the schematic clears things up.

Thanks for all the help!

Sam

 

Okay, after looking at the Ecoflow spec, here's a different (and likely better) approach:

Since the Ecoflow has an 1800W, 120Vac output (below) and you only need about 12V x 20A max = 240W (from your drawing), why not use a 120Vac to 12V power supply that can deliver more than 20A, such as this for example (it says to derate to no more than 80% of its rating).
With that you don't need to deal with an extra battery, concern about balancing the battery loads, or worry about whether you can charge it (which seems problematic).

What say?

 

Okay, after looking at the Ecoflow spec, here's a different (and likely better) approach:

Since the Ecoflow has an 1800W, 120Vac output (below) and you only need about 12V x 20A max = 240W (from your drawing), why not use a 120Vac to 12V power supply that can deliver more than 20A, such as this for example (it says to derate to no more than 80% of its rating).
With that you don't need to deal with an extra battery, concern about balancing the battery loads, or worry about whether you can charge it (which seems problematic).

What say?
View attachment 291900

I had thought about that. I just figured going dc to ac to dc would be inefficient. Am I wrong? Whenever I use the inverter on the ecoflow, fans start running too, which I presume only adds to the inefficiency. If you think it’s not actually that inefficient though, let me know!

Alternatively, I was thinking about trying to make a switch that uses the ac for the 12amps then seamlessly switches to the 8A dc port for the .5A draw for 10 hours. Do you think it’s possible to do this without interrupting the power supply to the heater? It’s ran by a computer it comes with, so I figure any interruption would just kill it.

 

Let's say that you didn't have your Ecoflow and you bought a rechargeable battery to run your heater for a couple of days before needing to be recharged. How would you recharge it? Most likely, you'd have a suitable charger for it that was powered from 120 VAC.

So how about getting a suitable charger for it and powering it from the 120 VAC from your Ecoflow?

Or get a suitable charger than can be powered from 12 VDC and power that from your Ecoflow?

As for your question about whether power will be drawn equally from the two if they are connected, the answer is almost certainly, No. Unless you use a circuit to actively manage things, you have virtually no idea how they are going to share the load. You might hope that 6 A from each goes to the load, but you could end up with 30 A coming from one with 12 A of it going to the load and the other 18 A going to the other battery.

It wouldn't take a lot to design a circuit that has two power inputs (one from the Ecoflow and the other from auxiliary battery) and one power output (to the heater) and it takes the first, say, 6 A from the Ecoflow and then limits at that current and takes anything above that from the auxiliary battery. That would double the amount of time between recharges on the auxiliary battery.

I would still recommend using an appropriate charger for that battery and not try to charge it directly from the Ecoflow's nominal 12 V output. Accept any inefficiencies involved. Depending on the battery chemistry you choose, you REALLY need to have an appropriate charge controller involved. It's not worth the risk to do it in some ad hoc way.

Now, if you were using something a lead-acid battery for your auxiliary (or some other pretty forgiving chemistry), building in a simple charge path from the Ecoflow to the auxiliary would be pretty simple.

 

Let's say that you didn't have your Ecoflow and you bought a rechargeable battery to run your heater for a couple of days before needing to be recharged. How would you recharge it? Most likely, you'd have a suitable charger for it that was powered from 120 VAC.

So how about getting a suitable charger for it and powering it from the 120 VAC from your Ecoflow?

Or get a suitable charger than can be powered from 12 VDC and power that from your Ecoflow?

As for your question about whether power will be drawn equally from the two if they are connected, the answer is almost certainly, No. Unless you use a circuit to actively manage things, you have virtually no idea how they are going to share the load. You might hope that 6 A from each goes to the load, but you could end up with 30 A coming from one with 12 A of it going to the load and the other 18 A going to the other battery.

It wouldn't take a lot to design a circuit that has two power inputs (one from the Ecoflow and the other from auxiliary battery) and one power output (to the heater) and it takes the first, say, 6 A from the Ecoflow and then limits at that current and takes anything above that from the auxiliary battery. That would double the amount of time between recharges on the auxiliary battery.

I would still recommend using an appropriate charger for that battery and not try to charge it directly from the Ecoflow's nominal 12 V output. Accept any inefficiencies involved. Depending on the battery chemistry you choose, you REALLY need to have an appropriate charge controller involved. It's not worth the risk to do it in some ad hoc way.

Now, if you were using something a lead-acid battery for your auxiliary (or some other pretty forgiving chemistry), building in a simple charge path from the Ecoflow to the auxiliary would be pretty simple.

Thank you for the great advice. It seems that a parallel system is the way to go. If I end up wanting to charge the new battery from the ecoflow, I’ll just do so with a charger from the ac ports.

You mentioned there might be chargers for the new battery that use 12vdc as input? That would most likely be more efficient, right?
Now for the question that I’ve seen answered elsewhere- can I be charging my battery from dc while using it to run the heater? This is essentially what I was trying to do all along.
Or would you just deplete the battery, charge it, then use it again?

 

Thank you for the great advice. It seems that a parallel system is the way to go. If I end up wanting to charge the new battery from the ecoflow, I’ll just do so with a charger from the ac ports.

You mentioned there might be chargers for the new battery that use 12vdc as input? That would most likely be more efficient, right?
Now for the question that I’ve seen answered elsewhere- can I be charging my battery from dc while using it to run the heater? This is essentially what I was trying to do all along.
Or would you just deplete the battery, charge it, then use it again?

While my first thought would be going DC to DC is more efficient than inverting DC to get AC, the efficiency of switching converters of most types has improved so much that I just don't know. It's probably going to depend on the specifics of the devices you are using.

As for whether you can charge the battery while using it -- sure. That's what the batteries in your car or your laptop (or other device that is battery powered but that you you can use while plugged in). But if the device you are charging it with can't provide as much current as needed, you aren't charging anything, merely reducing the rate at which the battery is being drained -- and you need a way to limit the current from the charger so that it isn't overloaded.

 

I had thought about that. I just figured going dc to ac to dc would be inefficient. Am I wrong? Whenever I use the inverter on the ecoflow, fans start running too, which I presume only adds to the inefficiency.

It will have some inefficiency, yes, but is that really a problem?
Doesn't the Ecoflow have more than sufficient capacity to operate the glow plug until you recharge it?

Do the fans run even when using low power from the 120V outlet, such as the 6W the glow plug uses most of the time?

Whether you use the Ecoflow 120V output to power the 12V supply, or use it to run a battery charger, the total efficiency will likely be similar.

 

Whether you use the Ecoflow 120V output to power the 12V supply, or use it to run a battery charger, the total efficiency will likely be similar.

thats a good point.
I think the fans run anytime the inverter is used.

 

I think the fans run anytime the inverter is used.

Then they would run when using a 120V battery charger also.