Hi all. I'm new here.

 

I've got a Rockrider EST900 and I want to fit a range extender battery that is ideally quite cheap, simple to fit, removable and not too big or heavy. I live in Northumberland and when I'm out in the hills I don't get much more than 20 miles. I've only come across a couple that might fit the bill:

 

Woosh bag battery 36V 10AH - https://wooshbikes.co.uk/?batteries - I could either fit this to the seatpost or strap it to the rack.

 

UPP bottle battery 36V 7AH - https://www.unitpackpower.com/product/s001-2-36v-7ah-bms20a-samsung-lg3500mah-cells-battery/ - This is the only one I've found that is small enough to fit on the frame (It's a small bike with a big battery)

 

Alternatively I could fit a second battery to the rack. I would have to strap it on somehow because it needs to be removable.

 

I can access the wires in the motor and I'm happy to do a bit of soldering. I know I'll need to fit a balancer/ideal diode so both batteries discharge in parallel. But I haven't done this before and I don't want to give the impression that I know what I'm doing!

 

I was just wondering if any of you guys have added budget range extenders like this, or if you have any advice or thoughts?

 

Thank you!

Edited March 9Mar 9 by MobyRick

How frequently do you envisage needing the extra range? and how inconvenient would it be to stop and swap out a 2nd battery pack? ( assuming you can buy spare batteries for your bike??)

 

Im not a battery expert but afaik Any circuitry you find to manage the concurrent connection of 2 x dis similar battery packs will need to handle both any differences in charge on initial connection as well as any differences in drain/discharge - between the packs without any detriment to either pack (ideally).

 

Might be cheaper to find a system to dynamically switch between packs?? most folk carry a 2nd battery when needed.

One big mistake is there: ideal diodes or even plain old diodes are for preventing problems during DISCHARGE of multiple batteries.

 

DO NOT charge multiple batteries from one charger, via linked output cables. Charge each battery separately using its proper charger. Otherwise you bypass the BMS and have an almost guaranteed battery fire.

How frequently do you envisage needing the extra range? and how inconvenient would it be to stop and swap out a 2nd battery pack? ( assuming you can buy spare batteries for your bike??)

 

Im not a battery expert but afaik Any circuitry you find to manage the concurrent connection of 2 x dis similar battery packs will need to handle both any differences in charge on initial connection as well as any differences in drain/discharge - between the packs without any detriment to either pack (ideally).

 

Might be cheaper to find a system to dynamically switch between packs?? most folk carry a 2nd battery when needed.

 

Thanks for your reply. I'd need the extra range pretty often. My bike has been discontinued so I may not find replacement batteries now. I'd rather not have to carry a full-sized second battery anyway. Yes the blender unit or

One big mistake is there: ideal diodes or even plain old diodes are for preventing problems during DISCHARGE of multiple batteries.

 

DO NOT charge multiple batteries from one charger, via linked output cables. Charge each battery separately using its proper charger. Otherwise you bypass the BMS and have an almost guaranteed battery fire.

 

Obviously I meant discharge, but thanks anyway for your lack of help.

How frequently do you envisage needing the extra range? and how inconvenient would it be to stop and swap out a 2nd battery pack? ( assuming you can buy spare batteries for your bike??)

 

Im not a battery expert but afaik Any circuitry you find to manage the concurrent connection of 2 x dis similar battery packs will need to handle both any differences in charge on initial connection as well as any differences in drain/discharge - between the packs without any detriment to either pack (ideally).

 

Might be cheaper to find a system to dynamically switch between packs?? most folk carry a 2nd battery when needed.

 

Yes the blender/diode should handle differences in charge and blends discharge so both batteries drain at the same rate. I was just wondering if anyone had done a similar DIY solution.

Im interested as to why tyou are only getting 20 miles on a 500wh, unless you have it set to maximum assistance.

Maybe even just one power setting lower might give you the range you need.

 

 

DO NOT charge multiple batteries from one charger, via linked output cables. Charge each battery separately using its proper charger. Otherwise you bypass the BMS and have an almost guaranteed battery fire.

THIS IS SPECIFICALLY BOSCH AND IM ADDING IT INCASE IN THE FUTURE SOMEONE HAPPENS BY TO FIND INFO

 

Just to add that some do, though it will be the highert end motors/batteries and there will be circuitry inside allows this to happen.

 

My Bosch performance cx gen4 has a 625wh battery as standard, and i have the option of adding a further 500wh, but this needs to be set up by the dealer(using Bosch diagnostic/set up interface, rather than me just plugging in the extra and trying to run or charge both.

When its set up correctly both batteries will charge as one using the same charger and input.

Yes the blender/diode should handle differences in charge and blends discharge so both batteries drain at the same rate.

Sag in differing batteries almost guarantees that won't really happen.... and don't bother thanking me (link).

Edited March 9Mar 9 by AntonyC

Y9u can add a range extender to most bikes as long as the main battery has some charge in it at the time of swi5ching on so that it can do any hand-shaking with the controller. After that, the controller wouldnknow the difference whether you have extender batteries or not. You can get a read6-made dual battery connector with the diodes in it from Aliexpress.

Im interested as to why tyou are only getting 20 miles on a 500wh, unless you have it set to maximum assistance.

Maybe even just one power setting lower might give you the range you need.

 

 

 

THIS IS SPECIFICALLY BOSCH AND IM ADDING IT INCASE IN THE FUTURE SOMEONE HAPPENS BY TO FIND INFO

 

Just to add that some do, though it will be the highert end motors/batteries and there will be circuitry inside allows this to happen.

 

My Bosch performance cx gen4 has a 625wh battery as standard, and i have the option of adding a further 500wh, but this needs to be set up by the dealer(using Bosch diagnostic/set up interface, rather than me just plugging in the extra and trying to run or charge both.

When its set up correctly both batteries will charge as one using the same charger and input.

Bosch have a twin battery arrangement aimed at the cargo bike market. The Comms allow the behaviour you describe when set up that way.

 

My point was to remove all doubt from the case of charging multiple generic two wire batteries via a single charger by leaving all switched on and connected.

 

This approach has burnt down flats and killed people.

Thanks for your reply. I'd need the extra range pretty often. My bike has been discontinued so I may not find replacement batteries now. I'd rather not have to carry a full-sized second battery anyway. Yes the blender unit or

 

 

Obviously I meant discharge, but thanks anyway for your lack of help.

Due to my advancing age and gradual mental decomposition my mind-reading capabilities are at present somewhat degraded.

 

I answered as I did to guarantee getting across the safety message. I deliberately would not try to answer your direct question until I know the safety message has landed.

 

Sorry if that upset you; not intended; going forward the forum works best if personal comments are avoided.

Due to my advancing age and gradual mental decomposition my mind-reading capabilities are at present somewhat degraded.

 

I answered as I did to guarantee getting across the safety message. I deliberately would not try to answer your direct question until I know the safety message has landed.

 

Sorry if that upset you; not intended; going forward the forum works best if personal comments are avoided.

 

You've certainly proved what a clever chap you are, and how adept you are at missing the point and contributing useless information. Well done.

I don't know about your bike specifically, but here's my experience of running parallel batteries for around eight years now.

I have a rear hub with rear rack battery. The second battery sits in the pannier and is connected via a simple Y splitter. The batteries are of similar capacity. This works well and gives me more range and less voltage sag around the Welsh hills. There are, however, some must do's when running this system.

The Y splitter MUST be disconnected for charging and batteries MUST be charged separately.

Before reconnecting the outputs of the two batteries together for use, the voltage of each battery MUST be measured individually (every time) and the voltage difference MUST NOT be more than 0.05v. Less would be preferable.

This works well in that there is far less strain on each individual battery as the current draw is roughly half from each battery.

There is a lot of debate about current flow from the output of one battery into the output of the other battery. A situation that would bypass the bms of the receiving battery and therefore dangerous. However, with batteries of similar capacity, I can't see why this would happen. Both are connected to the same load so if one goes lower in voltage then there will be less current drawn from it until the voltages equalise again. I have no measurements to back this up but the logic of ohms law seems pertinent here.

 

The alternative is to carry a second battery and change over the connection when the first is depleted.

 

As to mounting the second battery. If you found one that slides onto a DIN rail then you could mount a Din rail on the top of your rack. Slide the battery on and hold it with a couple of bungee straps. I did this on a recumbent and it worked well.

I recommend XT60 connectors for your Y splitter.

I don't know about your bike specifically, but here's my experience of running parallel batteries for around eight years now.

I have a rear hub with rear rack battery. The second battery sits in the pannier and is connected via a simple Y splitter. The batteries are of similar capacity. This works well and gives me more range and less voltage sag around the Welsh hills. There are, however, some must do's when running this system.

The Y splitter MUST be disconnected for charging and batteries MUST be charged separately.

Before reconnecting the outputs of the two batteries together for use, the voltage of each battery MUST be measured individually (every time) and the voltage difference MUST NOT be more than 0.05v. Less would be preferable.

This works well in that there is far less strain on each individual battery as the current draw is roughly half from each battery.

There is a lot of debate about current flow from the output of one battery into the output of the other battery. A situation that would bypass the bms of the receiving battery and therefore dangerous. However, with batteries of similar capacity, I can't see why this would happen. Both are connected to the same load so if one goes lower in voltage then there will be less current drawn from it until the voltages equalise again. I have no measurements to back this up but the logic of ohms law seems pertinent here.

 

The alternative is to carry a second battery and change over the connection when the first is depleted.

 

As to mounting the second battery. If you found one that slides onto a DIN rail then you could mount a Din rail on the top of your rack. Slide the battery on and hold it with a couple of bungee straps. I did this on a recumbent and it worked well.

I recommend XT60 connectors for your Y splitter.

 

Thank you! That's really useful.

 

I was always going to charge the batteries separately.

 

I'll have to look into what you said about batteries having similar capacity, thanks for the tip. My main battery is 14Ah but the second battery will probably be 10Ah.

 

Sounds like mounting on the rack could be easier than I thought. I'll look into that too!

Y9u can add a range extender to most bikes as long as the main battery has some charge in it at the time of swi5ching on so that it can do any hand-shaking with the controller. After that, the controller wouldnknow the difference whether you have extender batteries or not. You can get a read6-made dual battery connector with the diodes in it from Aliexpress.

 

Thank you! That's exactly what I'm aiming for. It's good to hear some positive confirmation.

 

Cheers

Sag in differing batteries almost guarantees that won't really happen.... and don't bother thanking me.

 

 

Im interested as to why tyou are only getting 20 miles on a 500wh, unless you have it set to maximum assistance.

Maybe even just one power setting lower might give you the range you need.

 

 

 

THIS IS SPECIFICALLY BOSCH AND IM ADDING IT INCASE IN THE FUTURE SOMEONE HAPPENS BY TO FIND INFO

 

Just to add that some do, though it will be the highert end motors/batteries and there will be circuitry inside allows this to happen.

 

My Bosch performance cx gen4 has a 625wh battery as standard, and i have the option of adding a further 500wh, but this needs to be set up by the dealer(using Bosch diagnostic/set up interface, rather than me just plugging in the extra and trying to run or charge both.

When its set up correctly both batteries will charge as one using the same charger and input.

 

Thanks for the info! The battery (and bike) is only a year old but yes I'm in the high power modes a lot, and I've been out on some cold days. I was surprised though. I need to sort it out because I'll be carrying full panniers on a trip soon. Nothing too ambitious, I just need to be sure it will do 25 miles while carrying some weight. Getting stranded doesn't bear thinking about!

Thanks for the info! The battery (and bike) is only a year old but yes I'm in the high power modes a lot, and I've been out on some cold days. I was surprised though. I need to sort it out because I'll be carrying full panniers on a trip soon. Nothing too ambitious, I just need to be sure it will do 25 miles while carrying some weight. Getting stranded doesn't bear thinking about!

 

Just to add, when it's fully loaded, the bike will need to be in sport or boost most of the time because of the weight. So it definitely wouldn't make 25 miles without a second battery.

First, you must check how many wires are connected to your battery connector on the controller side. If it's two, you can use any splitter arrangement. Without diodes, the batteries must be charged separately and only connected when at the same actual voltage. With the diode splitter, you don't need to worry about voltages or charging, but for safety's sake, it's better to connect at the same voltage if you can.

 

If you have multiple wires on the battery connector, some handshaking is required, which will only happen if the main battery has charge and meets the conditions required. In that case, you join the splitter wires to the two main wires. You can get these devices for any current and any number of extension batteries:

 

https://www.aliexpress.com/item/1005005310477337.html?src=google&pdp_npi=4%40dis%21EUR%2116.10%2112.29%21%21%21%21%21%40%2112000052392213126%21ppc%21%21%21&exp_tag=gcp&src=google&albch=shopping&acnt=272-267-0231&isdl=y&slnk=&plac=&mtctp=&albbt=Google_7_shopping&aff_platform=google&aff_short_key=UneMJZVf&gclsrc=aw.ds&albagn=888888&ds_e_adid=726717691648&ds_e_matchtype=search&ds_e_device=m&ds_e_network=g&ds_e_product_group_id=349615372002&ds_e_product_id=de1005005310477337&ds_e_product_merchant_id=107855927&ds_e_product_country=DE&ds_e_product_language=de&ds_e_product_channel=online&ds_e_product_store_id=&ds_url_v=2&albcp=22054759359&albag=172828878419&isSmbAutoCall=false&needSmbHouyi=false&gad_source=1&gad_campaignid=22054759359&gbraid=0AAAAAoukdWMd91ReilqeLkN-QaDhmQ3ku&gclid=Cj0KCQjw37nNBhDkARIsAEBGI8NSE1HB-G8WM9RZ09Qze0vsLx3wAVDIdOj8xV8LRJgrMf3F0X9pM10aApYbEALw_wcB&gatewayAdapt=deu2glo

Fantastic, thank you! I'll check the wiring.