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Parallel batteries?

Number3124

Silver Contributor
Member For 4 Years
So, I'm thinking of building an unregulated box mod. I'd like to run the batteries in parallel at the moment, but I want to know more about both parallel and series configuration before I get started. Understand the pros and cons of both a little better before I even think of designing or buying parts for it. I know that the short explanation is:

Parallel: Double your amps and mAh.
Series: Double your volts.

However, I've heard that parallel doesn't actually double your amps. I've also heard that unregulated series mods can be dangerous.

So, even if it's just links, more information would be extremely welcome.
 
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BoomStick

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Member For 5 Years
A parallel configuration splits the amp load between the cells. The voltage remains the same as a single cell, but a build drawing 20 amps total gets 10 amps from one battery and 10 from the other. If you're planning to use it at wattages under 100, I'd build a parallel box. If you're going above 100 watts, you might want to consider series. Personally, 100 watts is more than enough for me. I'd build a parallel box and take advantage of the amp load splitting. Also battery university says using perfectly matched cells is less critical when using a parallel configuration as opposed to series. I take that to mean slightly safer. I see no reason to use series unless you're using a chip that requires the higher voltage to operate or if it's unregulated, you're trying to make crazy big power.
 

Number3124

Silver Contributor
Member For 4 Years
A parallel configuration splits the amp load between the cells. The voltage remains the same as a single cell, but a build drawing 20 amps total gets 10 amps from one battery and 10 from the other. If you're planning to use it at wattages under 100, I'd build a parallel box. If you're going above 100 watts, you might want to consider series. Personally, 100 watts is more than enough for me. I'd build a parallel box and take advantage of the amp load splitting. Also battery university says using perfectly matched cells is less critical when using a parallel configuration as opposed to series. I take that to mean slightly safer. I see no reason to use series unless you're using a chip that requires the higher voltage to operate or if it's unregulated, you're trying to make crazy big power.

Okay. Thanks. Might eventually make a series, but parallel sounds like a good place to start. Thanks.

So I heard something about parallel configuration not actually splitting the load evenly. Is there any truth behind that?
 

BoomStick

Gold Contributor
Member For 5 Years
I imagine that would depend on how balanced the resistance of the circuit is and how perfectly matched the cells are. If everything was perfectly equal the amp load should be perfectly split. Certainly there are minor variations that will have some effect, but two twenty amp cells would have to be ran pretty hard for any problems to arise if the box is built well and a set of quality, matched cells are used. 4.2v and 30a gives you 126w which still leaves 5a per cell on the table using two 20a batteries, so for sane person vaping you would be well in the safe zone even going that high in power.
 

Number3124

Silver Contributor
Member For 4 Years
I imagine that would depend on how balanced the resistance of the circuit is and how perfectly matched the cells are. If everything was perfectly equal the amp load should be perfectly split. Certainly there are minor variations that will have some effect, but two twenty amp cells would have to be ran pretty hard for any problems to arise if the box is built well and a set of quality, matched cells are used. 4.2v and 30a gives you 126w which still leaves 5a per cell on the table using two 20a batteries, so for sane person vaping you would be well in the safe zone even going that high in power.

Awesome. Thanks. I wasn't sure how uneven the load split might be. I'm planning on using VTC4s in the box so if I don't attempt to draw more than say 50 amps at 4.2v (not that I actually am; that would be 0.8 ohms and 210W) the head room should be sufficient to not have a nice little bomb in my hand. Thank you for the help.

I'm going to be researching the various types of wires, soldering techniques, and other parts that go into a box mod before moving on.

Thanks again.
 

Jon@LiionWholesale

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The most important thing is to be ultra vigilant that your batteries are well matched. On first use you could see how even the discharge is by comparing voltage of the cells after using it for a while. If it's bad try another cell. Then definitely keep each pair of batteries paired for life after the first use or two and if you have to replace one replace them both.

Assuming your wiring is matched and the cells are matched everything should draw evenly.

And leaving more headroom then you would just using a single cell is smart, sounds like you're doing that.
 

Number3124

Silver Contributor
Member For 4 Years
The most important thing is to be ultra vigilant that your batteries are well matched. On first use you could see how even the discharge is by comparing voltage of the cells after using it for a while. If it's bad try another cell. Then definitely keep each pair of batteries paired for life after the first use or two and if you have to replace one replace them both.

Assuming your wiring is matched and the cells are matched everything should draw evenly.

And leaving more headroom then you would just using a single cell is smart, sounds like you're doing that.

Thanks for the response. I haven't actually gone ahead with this. I'm still planning out the build. I'm planning on ordering something in the range of four or five pairs of VTC4s after I get the built and taking any cells that don't match well and using them in tubes or just giving them to friends.
 

Jackson

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So, I'm thinking of building an unregulated box mod. I'd like to run the batteries in parallel at the moment, but I want to know more about both parallel and series configuration before I get started. Understand the pros and cons of both a little better before I even think of designing or buying parts for it. I know that the short explanation is:

Parallel: Double your amps and mAh.

I've also heard that unregulated series mods can be dangerous.

.
'However, I've heard that parallel doesn't actually double your amps'

Sure it does. I've also seen that statement.

From Battery University:

Parallel Connection

If higher currents are needed and larger cells with increased ampere-hour (Ah) ratings are not available or the design has constraints, one or more cells are connected in parallel. Most chemistries allow parallel configurations with little side effect. Figure 3 illustrates four cells connected in parallel. The voltage of the illustrated pack remains at 1.2V, but the current handling and runtime are increased fourfold.

From Batteries Northwest concerning automotive applications:
In PARALLEL CONNECTION, batteries of like voltages and capacities are connected to increase the capacity of the battery bank... The final voltage remains unchanged while the capacity of the bank is the sum of the capacities of the individual batteries of this connection. Amp-Hrs, Cranking Performance and Reserve Capacity increases while Voltage does not.
 

Number3124

Silver Contributor
Member For 4 Years
'However, I've heard that parallel doesn't actually double your amps'

Sure it does. I've also seen that statement.

From Battery University:



From Batteries Northwest concerning automotive applications:

Okay. Excellent. Thank you.
 

Slurp812

Bronze Contributor
Member For 4 Years
I agree ^^. Two vtc 4's could do 60 amps in parallel. That would be around 200 watts!!!
 

Number3124

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Member For 4 Years
I agree ^^. Two vtc 4's could do 60 amps in parallel. That would be around 200 watts!!!

More than that. If I just wanted to see how much power I could make with no regards to head room, at full charge, 4.2V, 60amps, 0.07 ohms, 252 watts. That said, I like not charring my lungs.
 

Jackson

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More than that. If I just wanted to see how much power I could make with no regards to head room, at full charge, 4.2V, 60amps, 0.07 ohms, 252 watts. That said, I like not charring my lungs.
Well you can't be using 4.2V for your calculations, just ain't happening at .07Ω.. Maybe about 160W
 

Number3124

Silver Contributor
Member For 4 Years
Well you can't be using 4.2V for your calculations, just ain't happening at .07Ω.. Maybe about 160W

Yeah it is. (4.2V^2)/0.07ohm.

4.2*4.2=17.62

17.62/0.07=252

So, at 0.07ohms you're drawing 60 amps at 4.2. A dual parallel with 30 amp batteries can give you 252watts at max power. You shouldn't but you can.
 

Jackson

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Yeah it is. (4.2V^2)/0.07ohm.

4.2*4.2=17.62

17.62/0.07=252

So, at 0.07ohms you're drawing 60 amps at 4.2. A dual parallel with 30 amp batteries can give you 252watts at max power. You shouldn't but you can.
Ever done or seen any loaded volts tests? You can't can't just use 4.2V, the voltage used in the equation has to be measured , with a .07Ω load, then the amps and watts can be calculated. About ~3.3V maybe.
 

Number3124

Silver Contributor
Member For 4 Years
Ever done or seen any loaded volts tests? You can't can't just use 4.2V, the voltage used in the equation has to be measured , with a .07Ω load, then the amps and watts can be calculated. About ~3.3V maybe.

I'll agree with this.
 

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