Adding a second battery to eliminate sag."Battery Blender"or parallel?

James340

10 mW
Joined
Feb 20, 2024
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23
Location
Aguila Arizona USA
I have been using the batteries individually by manually connecting one then the other.During heavy demand it seems to sag using one battery at a time.These are same voltage and about the same usage but one is 4p the other 5p.I have another bike setup for dual batteries but they are the same voltage/Capacity.I Googled this question but nothing worthwhile came up.
 
May not need a "Battery blender." Simplest and safest setup is for both batteries to have single port BMS (Charge and discharge ports both connect to the same tabs on the BMS). Separate port BMS makes things more complicated.

Many threads here on ES describe paralleling battery packs.
 
A battery blender won't help with voltage sag in the same way that paralleling will. Paralleling basically combines the discharge rates of the two packs so it will cut sag in half under the same conditions. Both the blender and paralleling benefit from not discharging one of the batteries too low if your trip only requires on pack's worth of charge (two half charged packs vs a single fully discharged pack). The advantage of the blender is that you can connect the two batteries together without worrying about frying something, while paralleling requires you to make sure both packs are at the same voltage before connecting them.

Your next question should be, as 99t4 alludes to, is how you'll be charging the packs. The blender would allow you to charge each pack with it's own charger, while still connected to the blender (think of the blender as being a few diodes that prevent current from one pack flowing into the other. It's actually performed by MOSFETs in some/most blenders). Charging parallel pack may, or may not, be more complicated or dangerous, but you should be very comfortable that you know what you are doing or what could go wrong before attempting it, and have a well thought out routine to follow.
 
May not need a "Battery blender." Simplest and safest setup is for both batteries to have single port BMS (Charge and discharge ports both connect to the same tabs on the BMS). Separate port BMS makes things more complicated.

Many threads here on ES describe paralleling battery packs.
Thanks for your help
 
A battery blender won't help with voltage sag in the same way that paralleling will. Paralleling basically combines the discharge rates of the two packs so it will cut sag in half under the same conditions. Both the blender and paralleling benefit from not discharging one of the batteries too low if your trip only requires on pack's worth of charge (two half charged packs vs a single fully discharged pack). The advantage of the blender is that you can connect the two batteries together without worrying about frying something, while paralleling requires you to make sure both packs are at the same voltage before connecting them.

Your next question should be, as 99t4 alludes to, is how you'll be charging the packs. The blender would allow you to charge each pack with it's own charger, while still connected to the blender (think of the blender as being a few diodes that prevent current from one pack flowing into the other. It's actually performed by MOSFETs in some/most blenders). Charging parallel pack may, or may not, be more complicated or dangerous, but you should be very comfortable that you know what you are doing or what could go wrong before attempting it, and have a well thought out routine to follow.
Thanks for your help.I will charge batteries separately.I was going to install Ideal Diode's but if paralleling only requires the batteries be at the same voltage.That is a simple task to plan ahead for.
 
Thanks for your help.I will charge batteries separately.I was going to install Ideal Diode's but if paralleling only requires the batteries be at the same voltage.That is a simple task to plan ahead for.
Don't forget to incorporate 99t4's guidance on the BMS's.
 
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Really need more information about the batteries or what's inside the plastic boxes ? Like what type of cells to each of them have ? And what type of capacity should each one have ? Like where did you get them ?
 
Really need more information about the batteries or what's inside the plastic boxes ? Like what type of cells to each of them have ? And what type of capacity should each one have ? Like where did you get them ?
Both batteries have 21700 cells.1 st battery is a UPP 10s4p 2 nd battery is a Litokala 10s5p.Aliexpress.
 
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