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Add extra battery

Old 07-01-21, 02:35 PM
  #1  
Bigbadjohn
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Add extra battery

I have a 36v ebike I want to add an extra 36v battery where would I connect the terminal to from the extra beattery also so they can both charge at same time
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Old 07-02-21, 04:19 AM
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Trying to add an extra battery can cause a lot of problems if it isn't done right. I normally just carry an second battery when I need extra range and swap out when the first one dies. Less weight for trips where you don't need two, and fewer failure points under all circumstances.

One of my bikes does have the factory-fitted dual battery setup, but it isn't a big deal compared to just keeping it simple and swapping out two batteries with a standard single mount.

Last edited by hydrocarbon; 07-02-21 at 04:23 AM.
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Old 07-02-21, 04:42 AM
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Originally Posted by Bigbadjohn View Post
I have a 36v ebike I want to add an extra 36v battery where would I connect the terminal to from the extra battery also so they can both charge at same time
You need to connect them parallel. I don't know what battery connectors you have, so I can't say which wires that is on your bike.

If they are connected parallel, they can both charge at the same time. However, if you have double the capacity, it will take twice as long to charge. You could unplug one, and use two chargers.

As suggested, consider using one, then swapping.
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Old 07-02-21, 05:27 AM
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Be very careful plugging two batteries together. If they are at different charge levels you will get a massive spark and possibly a fire.

Not trying to scare you away, just trying to let you know it is going to take much more knowledge and care than just how to connect the wires.
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Old 07-02-21, 07:18 AM
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There could also be a problem if the batteries are composed of different cells or if their state of wear differs. As above, better to use independently unless they are tha same and connected when new and kept "together".
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Old 07-02-21, 07:33 AM
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Don't you need a controller that can handle two separate, parallel circuits? or at least add a switch that allow you to change between the parallel circuits of two batteries.
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Old 07-02-21, 08:56 AM
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Originally Posted by cat0020 View Post
Don't you need a controller that can handle two separate, parallel circuits? or at least add a switch that allow you to change between the parallel circuits of two batteries.
You could normally run one controller with two batteries. If you had two motors, you would need two controllers.

You don't have to have a switch. You could just unplug one, and plug in the other.
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Old 07-02-21, 09:42 AM
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It's possible (I rode a BH) to have two motors with one controller using a "splitter". Also possible to have two batteries with one motor and one controller, but the batteries should be the same.
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Old 07-02-21, 11:35 AM
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uh, no. I'll scare you off. Its a potential fire hazard (and you really, really don't want a Li-Ion fire - ever seen a tesla that burned??? (or the house it was in?)).
when you connect the two batteries, they will immediately try to equalize - with one battery charging the weaker battery - this will likely charge the battery too fast and can potentially cause serious problems.

It can be done (if you are an EE or equivalent), but you need to make sure you don't have a sudden unintended current flow. I'd say, if you have two identical batteries (including age) that are hot off the charger, its probably a low risk - but start changing anything and the risk goes very high.
At $15 a charger, I have two chargers - clearly charging two separately is going to take half the time then charging both off of one charger.

Me, I just carry two batteries, and switch from one to the other half way through the ride.
Ebike.ca did develop a cool little reserve tank battery that was designed to be used in series and you could plug and play as you liked. That would make a nice little reserve tank, but they were not cheap. Their primary goal was to make a battery small enough that you could ship it without incurring the Li-Ion shipping tax.

What specifically is your goal? Doubling your ride time? having a small reserve tank?

Originally Posted by hydrocarbon View Post
Trying to add an extra battery can cause a lot of problems if it isn't done right. I normally just carry an second battery when I need extra range and swap out when the first one dies. Less weight for trips where you don't need two, and fewer failure points under all circumstances.

One of my bikes does have the factory-fitted dual battery setup, but it isn't a big deal compared to just keeping it simple and swapping out two batteries with a standard single mount.
Yeah, what he said!
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Old 07-02-21, 12:43 PM
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Don't do it. All the previous posts point out the potential dangers.

If you need more power/range just get a single pack with a higher Amp-hour rating. I recently upgraded to 25% more powerful pack when the old one failed. This is simple if you are riding a conversion with generic ebike components.

But if you have a factory ebike with a unique proprietary battery design you are probably stuck with carrying a spare and swapping packs when the first is run down.
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Old 07-03-21, 08:46 AM
  #11  
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Originally Posted by MNebiker View Post
But if you have a factory ebike with a unique proprietary battery design you are probably stuck with carrying a spare and swapping packs when the first is run down.
Seems like there should be ways around proprietary battery packs. While the mount might be unique and not worth the effort to adapt, seems like it should be possible to wire in a different connector to allow different batteries. Might take some MacGyver skills to get to the wiring. Only possible road block would be if the controller somehow talks to the battery. I've heard rumors of that on some bikes.
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Old 07-03-21, 12:20 PM
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Originally Posted by Pop N Wood View Post
Seems like there should be ways around proprietary battery packs. While the mount might be unique and not worth the effort to adapt, seems like it should be possible to wire in a different connector to allow different batteries. Might take some MacGyver skills to get to the wiring. Only possible road block would be if the controller somehow talks to the battery. I've heard rumors of that on some bikes.
If the intent is to use the second battery to extend the range there is a way that both batteries could be wired to a single controller and be made reasonably fail-safe. I did consider this option at one point, but when the smaller pack failed I just bought a bigger pack. However, this could be a low-cost workable option:

Connect each battery to one side of a heavy-duty Double-Pole, Double-Throw toggle switch with a neutral center position. This would provide a simple means to switch batteries without the possibility of the batteries ever being connected together, and would also give a neutral off position that shuts everything down. As chas58 stated, use 2 chargers to charge each battery individually. I would still incorporate a plug and socket in each battery lead so that they could be removed separately if needed. House the switch in some sort of minibox to protect the connections - maybe tuck it up under the seat or on the rear rack, etc. Get someone with basic electronics knowledge to wire it up if you are unsure how to do it.

Easy to do on a bike with generic parts - might need to get a bit innovative on proprietary system.

Just a thought - Use at your own discretion and risk. . . . . .
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Old 07-04-21, 06:13 AM
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Originally Posted by MNebiker View Post
If the intent is to use the second battery to extend the range ...
No I was thinking more in terms of having a greater range of replacement options than sticking with a proprietary unit. Not sure what the OP is looking for.

As for using two chargers, if the batteries are hooked up one at a time then yeah, charge them separately. If they are paralleled and hooked up together, than no, keep them connected and charge them with a single charger. Bigger batteries can take a higher charging current reducing charging time.
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Old 07-16-21, 11:16 PM
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Lightbulb

You need to connect them parallel. If the intent is to use the second battery to extend the range there is a way that both batteries could be wired to a single controller and be made reasonably fail-safe.
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Old 07-17-21, 11:09 AM
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I think OP passed out

Or fell asleep, or tried what he was thinking of and something predictable happened after the first post.
Maybe looking for an alibi.
7 years on the forum and he still gots sum larnin' to do .

Sorry , children.

Last edited by bikebikebike; 07-17-21 at 11:14 AM.
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Old 07-17-21, 11:55 AM
  #16  
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No, BidbadJohn is currently asking a question about a noisy motor, so he's still here.
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Old 07-17-21, 03:22 PM
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I currently run four batteries in parallel for long distance touring. I do not recommend doing this even though I do it.

I have done everything wrong and gotten away with it. I have since taken more measures to insure that I don't do stupid things accidently.
I have taken more measures to insure safety when charging. It would take too many words to describe everything you can do to increase safety. In the end though, the setup is not as safe as a single battery.

My total is 2,538 watt hours and I charge with a single 15 amp charger. Each battery is charged through it's own BMS

Why do I bother? Because I can and the range is greatly extended due to the lack of battery sag. I can in a pinch run decent power all the way down to the 20% remaining point with out having to seriously reduce power to get it. I have not needed to do that yet but I can. I can pull pretty significant power from the batteries when I am touring on dirt at 20 mph or so for long distances. My range is a good 10-15% higher than using the batteries separately.. The weight and bulk of the singe charger is better than the four chargers I would need to carry to duplicate the charge time.

Here I am charging all four batteries in a picnic pavilion while having lunch.
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Old 07-18-21, 02:03 PM
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I'm curious.. what is the distance that you travel on your 4-battery e-bike regularly?

and how often do you repeat such ride distance? few times a week? few times a month?

I see a trailer getting pulled in the back, how much weight are you pulling with your 4-battery e-bike?

Terrain along your regular long distance ride, how much altitude change along the distance?
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Old 07-18-21, 05:25 PM
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Originally Posted by cat0020 View Post
I'm curious.. what is the distance that you travel on your 4-battery e-bike regularly?

and how often do you repeat such ride distance? few times a week? few times a month?

I see a trailer getting pulled in the back, how much weight are you pulling with your 4-battery e-bike?

Terrain along your regular long distance ride, how much altitude change along the distance?
My fat e bike is set up for touring but I regularly ride it about 150-200 miles a week locally. 100 miles a day is fairly easy for me to ride and 150 is a stretch. To gawk, I normally shoot for 80 miles a day on touring.. With the four battery system I can travel at 18-22 mph. for 80-100 miles between charges. I have used as much as 4,000 watt hours in a single day with 2.5 hours of charging. on rough off road traveling at higher speeds.
In the photo above, I was the sag wagon, I had all of the camping gear, the food, the cooking stuff, the extra drinks and the cloths. The weight is 82 lbs for the bike, 200lb for me and the trailer is at 145lb. total is 425+lb
Vertical climbing can vary considerably from 500 to 10,000 feet per day. Grades regularly exceed 10% and rarely exceed 25%.
Deep snow and cold temps gives the lowest range. As low as 55 miles.
My change in attitude and what I will tackle has amazed me. The lack of range anxiety and rugged capability has made a huge difference in my fun factor

Have to admit that the last two weeks I have not ridden much as I got a new puppy.
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