batteries in parallel and battery in a backpack options...

Dear all,
I am trying to upgrade my ebike as it has a 1300w middrive motor and only a 48v 15ah battery.

The manufacturer said I cant add and put another identical battery in parallel as it can cause problems.
Has anyone put two batteries together in parallel, and are they ok?

Also, as I have been told they wont help me with this and my frame is too small to put on bigger batteries and I use the rear rack as a seat for my daughter, I am looking into buying a 60v 20ah and attaching it to a backpack.
Also, anyone got any experience with this?

Thanks

superebike said:

The manufacturer said I cant add and put another identical battery in parallel as it can cause problems.
Has anyone put two batteries together in parallel, and are they ok?

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Electrically it's fine. Be sure to match chemistry and # of cells in series. Gas gauging and charging may work differently though.

Also, as I have been told they wont help me with this and my frame is too small to put on bigger batteries and I use the rear rack as a seat for my daughter, I am looking into buying a 60v 20ah and attaching it to a backpack.

Click to expand...

That's a lot of weight to put in a backpack. Also, I would not do a "homemade battery" for this application - putting a potentially flammable/explosive battery on your back, between you and your daughter, might not be the best idea.

Thanks for your reply, its only 6 kilos, and takes weight off the actual bike, so I dont think it will be an issue.
The battery isnt home made, so no worries there...

I rode with my second, 12 lb battery in a backpack on my back for a 32 mile ride and regretted it for about 2-3 weeks. It did not seem bad at all on the ride but the next day....look out. It was not a Lithium Ion chemistry but was Lithium Iron Phosphate. That 2nd battery now resides in the triangle run in Parallel with no issues. I charge them separately as they both have internal BMS's.

Thanks for your feedback. I am thinking of putting padding in the backpack, and wearing it front side instead of on the back where there are delicate vertebra... Do you not think that would help? Was it pain from the impact or the weight?
Thanks

The manufacturer does not want to warranty damage caused because you paralleled two batteries wrong. So they say no. It will mean if anything does go wrong with your battery later, they will need to not be told you paralleled it.

When you hook it up, they both need to be full charged, and of course they need to be close to identical. Same type of cells, same voltage when fully charged. AH size does not matter, but everything else does.

Hook up a charged battery to a discharged one by mistake, and the charged one charges the other through the bms, with the current going the wrong direction through it. This can potentially damage it. This is why they said no.

superebike said:

Thanks for your feedback. I am thinking of putting padding in the backpack, and wearing it front side instead of on the back where there are delicate vertebra... Do you not think that would help? Was it pain from the impact or the weight?
Thanks

Click to expand...

It was the weight, not any impact. I really didn't feel any problems on the ride, just the beginnings of something not good a few hours afterwards and the next day was just about a stay in bed day. I would guess that whether you have it in front or back, your body will be compensating and using different muscles or using muscles in a different way and you later feel the strain. But maybe if you do it for a long period of time, your body might be ok after a "training" period.

Both my parallelled batteries are key switched so I can ride on one or the other or both. I have a CA Vers 3 so using the key switches separately, I'm able to verify my 2 packs Voltages the next day after charging before turning both switches to connect them in parallel. They are 52 Volt packs and are always no more than .1 Volt apart.

Thanks Dogman dan and bvh!!

Now I understand it all. I will buy another 48v-15ah-720kw/h battery which will go on the top tube, and have me a nice 48v-30ah beasty with this 1300w midrive!

I enjoy the bike now, but anything above 4 pas out of 9 and the battery just gets eaten up. On pas 9 i can only get 15km out of the battery, but it feels so good being used at top output!
I think having 720 kw/hr-2=1440kw/h will give so much more endurance and power, as right now the motor eats into the batteries I feel.

Thanks so much...

BVH,
Thanks so much. Where can I get one of these key switches?
Nial

Could be tricky finding key switches that will handle 50 Volts and 30-50 Amps. It might be easier to use toggle switches rated for 48 VDC and current. I'm assuming you want a switch for each pack. If this is the case and you will always run the batts in parallel then 30 Amp switches are probably good if you keep total current to under 60 Amps. Just be sure the switches (or one switch if you are simply making a System On-Off switch) are rated for the max current you will run thru them.

My key switches came with my Prodecotech bike batteries. They are a 3-position switch with the first position being one that locks and unlocks the physical battery onto the rack for anti-theft reasons. Second position is electrically OFF and third is ON. You could call Prodecotech in FL and try to order two switches by themselves. They come in the rack assembly but might be available separately. I would assume they are rated for 52 Volts and 30 Amps. But any toggle sufficiently rated will work for you and would probably easier to mount requiring a smaller space.

BVH, Thanks so much for your info.

I live in Spain, so I will find a way to get the toggle switch with 48v specifications-with 30amps output-so as you say upto 50amps potential.

I assume my mid drive 1300w motor will be able to cope with the extra ampage, as I will connect it to be 48v and 30amps. What motor do you have, and what specs?

So, now its more clear. I can set up each battery with its toggle switch to measure its charge on the cycle analyst, so as to have it close to the other batterie in parallel and be within 0.1 volts of each other.

When you have both batteries switched on, does the cycle analyst show the accumulated voltage of the 2 batteries total?

Many thanks

Just to be clear and that I'm interpreting your post correctly:

You said:
I live in Spain, so I will find a way to get the toggle switch with 48v specifications-with 30amps output-so as you say upto 50amps potential.

The "up to 50 Amps potential" would be only if you are using a 30 Amp switch on each battery and both batteries are actually being run in Parallel together. You would not want to pull any more than 30 Amps if you're running only on one battery. And be sure your batteries are capable of discharging at a 30 Amp rate.

I have a Prodecotech brand - obviously made for them by someone else so I really don't know what motor I have other than it is rated by Prodecotech as a 1000 Watt direct drive motor.

You said:
So, now its more clear. I can set up each battery with its toggle switch to measure its charge on the cycle analyst, so as to have it close to the other batterie in parallel and be within 0.1 volts of each other.

Yes to the above and you could probably get away with .2 or .3 Volt difference but certainly .1 or less is always better. The Since you're running in Parallel, you double Amp Hours, not Voltage so the CA will only see your two packs in parallel as one big pack of the single pack Voltage.

Sorry, didnt see yor reply until now.

Yes, I mean upto 50amps for the combined batteries in parallel. Each battery is only 15amps so this will be fine.

Right, upto a small variance as upto 0.3v is acceptable. Is it really that essential to be so close? I say this as my CA is not always 100% accurate.

I just realised I dont think I need another toggle switch as my hailang batteries come with on off. So I am presuming just setting the bvatteries in parallel can be done with just the cables being connected and nothing else?

I might post this question on other boards as I am about to buy the second battery.

Many thanks

Dear All,
I just want to double check this.

I want to connect a 2nd battery in parallel. The second battery is the same as the other 15amp by 48v, on a 1300w motor.

They are hailang batteries, so I am assuming that as they have on off switches and will be connected to a cycle analyst, its a simple case of attaching the cables in parallel?

Is this right, or am I wrong?

Any info would be great, especially from people with experience.

Many thanks
Nial

It can be done. The only thing I would caution about is to make sure they both have close to the same voltage before connecting them to each other. If one pack was much higher than the other, you could get destructively high current flow as the higher one tries to charge the lower one. You should also disconnect them for charging and charge separately. You could charge both at the same time while connected, but the BMS would only be watching one pack and not be able to detect a problem with the other pack.

If both your batteries are already switched, then you're good to go in that respect.

.3 Volts difference is just a number that I use as a maximum. The higher the difference, the more high current flow there will be between batteries when you connect them via the switches. arcing within the switch will be greater with higher current flows and you might kill your switches faster and you could incur higher current flow than your batteries are rated for or the cables can handle. There's lots of variables in this calculation like cable size, battery current ratings etc. If you're using the CA to measure both batteries, then it will be super accurate - relatively speaking. The CA may not agree with a precision bench meter but 48 Volts measured with your CA on battery and 47.8 measured on your same CA on the other battery will mean that they are truly only .2 Volts difference, plus or minus a fraction.

Thanks so much BVH,

Great, so I can rely on the CA being accurate. Perfect.

Well, I should have the new battery arive in 10 days. I will let you know when I have it running. Looking forward to it so much.

Thanks again for your help. Your a star!