Topping up a lithium battery with a second battery

Has someone had experience (eg a caravanner or 'boater') of topping up an ebike battery using another battery and lightweight inverter. I'm just thinking ahead of possibly wanting to top up my Decathlon e500 battery for longer runs or 'emergency'. I can't delve into the innards of the battery pack or controller whilst it is still under warranty. I understand the inverter must be a pure sine type but otherwise?

There are a few ways of doing that. This Bestek pure-sine inverter is proven to work well, you can buy a 12v to 42v charger to run directly from a 12v LA or lithium car/boat/campervan battery (a more efficient method minimising conversion losses), or use a stand-alone power-pack (aka solar generator) from the likes of Eco-flow, Jackery or Bluetti etc.

 

I use both pure-sine and modified sine inverters from vehicles/other lithium batteries, and/or a Bluetti EB70. All work without any issues.

In my pre-solar days, I used a 150W Sterling Power pro power q quasi sine wave inverter to power my Shimano slow 1.8A charger with no issues.

 

Mine was £15 in a sale on the Sterling Power website, cheap as packaging was damaged. New price is about £60 to £75 these days. I wouldn't use a cheap Chinese non-sine wave type.

Thanks for the advice. I do have an old (working) Nikkai 150W (continuous) inverter so I'll give it a try with the car battery. I wondered whether the 150W output was sufficient output to use with the nominal 1.8A charger. Peter

A 1.8A charger should be outputting around 80w at 40v. Allow for inefficiencies gives 100W input. That should leave plenty of headroom with a 150W charger; assuming it's decent quality and really means continuous when it say so.

Thanks for the advice. I do have an old (working) Nikkai 150W (continuous) inverter so I'll give it a try with the car battery. I wondered whether the 150W output was sufficient output to use with the nominal 1.8A charger. Peter

Yes, 1.8A at maximum 42V is only 76W, so even allowing for modest efficiency in both inverter and charger it should be fine.

 

Just keep an eye on it the first time to check nothing odd happens.

you can buy a 12v to 42v charger to run directly from a 12v LA or lithium car/boat/campervan battery (a more efficient method minimising conversion losses

 

Is this the type of thing ?

 

https://www.ebay.co.uk/itm/173772977403?hash=item2875ad34fb:g:7VUAAOSwrg1iBUaf&amdata=enc%3AAQAHAAABIPWibupuFyJwH3ZvobF3nueHPnKCZShEawLWnQ66RqrAi1KjQXY2QGnzRbozl1LD%2BbfqCkMlr0JCOaZW7Co5blH7bUH3nDTfqe9sOWtrpRy8yS6g%2FNrz8jxvPgAn5Jq1WFPfqFWYhMa8PEWfIhmulC%2FqHydggP%2BUUApSr4FpVYQuEsAZaYN0px6gZsOGePWzCYo3kYZWJmPdCPwdZmI0gCw%2FUDBqs%2BEc%2F5SITngUAaWx9uMVrMA6nC9N9VH1ux5%2BcnNFV7vJU3PKnw7pEZdby52jwQ8GuZYPaY1Jxwc4BAI2w7ZD5bjpm5Bn07bOin%2BvToiaDe8zTTuSBvu7Bj2Fyjgd4h8uOZB40yUB%2BTKjbnPpV7so%2B9xmd7yXuwXjgSqHJg%3D%3D%7Ctkp%3ABk9SR9aG9N_nYQ

Is this the type of thing ?

Yes. Some bike makers offer their own versions too (Wisper, Bosch etc).

This Bestek pure-sine inverter is proven to work well, you can buy a 12v to 42v charger to run directly from a 12v LA or lithium car/boat/campervan battery (a more efficient method minimising conversion losses), or use a stand-alone power-pack (aka solar generator) from the likes of Eco-flow, Jackery or Bluetti etc.

 

Those Besteks are a bit pricey now, so I thought I'd better grab this while it's cheap, to run my electric blanket powered by my ebike battery, while resting in between gardening this winter. It'll also enable my ice cream bicycle trailer man transformation, provide power to a beer fridge and mobile disco in the summer...

 

 

Edited December 17, 20232 yr by guerney

It doesn't make sense to use an inverter because you're double converting - say from 12v to 240v, then 240v to 36v. It's much simpler, cheeper and more efficient to use universal charge controller board or a step-up/down buck converter with current control.

https://www.ebay.co.uk/itm/392248280526?hash=item5b53d1c5ce:g:KBEAAOSwdLhb~mMo&amdata=enc%3AAQAIAAAA0PlT95LqwZya22a1UbK0oCuVz5jERR525T%2F8Ap7j9KRHVS1AAI3pnhRC2NoRLG71kbdMCfFcrgKABpiv%2FHHhMQ342tHWZFuQfgPmczG8199NVw7X%2FH2D0jvO750PazS2A0%2BSNE6bGFTRh70%2FhOstmBf0Cb1Pe4XchlW9ch9pz2Szc7RjY8CRiHO8IQkSxplTbhh%2FI5QR5Da00Hb9y16JvX5DBtit10cBOLcYgepBtjvGo87lN3CaLPG5sR5cXO%2FPzC6SsF8DzfFOiPM2%2F3Cpai0%3D%7Ctkp%3ABk9SR8LQuqOPYw

It doesn't make sense to use an inverter because you're double converting - say from 12v to 240v, then 240v to 36v. It's much simpler, cheeper and more efficient to use universal charge controller board or a step-up/down buck converter with current control.

https://www.ebay.co.uk/itm/392248280526?hash=item5b53d1c5ce:g:KBEAAOSwdLhb~mMo&amdata=enc%3AAQAIAAAA0PlT95LqwZya22a1UbK0oCuVz5jERR525T%2F8Ap7j9KRHVS1AAI3pnhRC2NoRLG71kbdMCfFcrgKABpiv%2FHHhMQ342tHWZFuQfgPmczG8199NVw7X%2FH2D0jvO750PazS2A0%2BSNE6bGFTRh70%2FhOstmBf0Cb1Pe4XchlW9ch9pz2Szc7RjY8CRiHO8IQkSxplTbhh%2FI5QR5Da00Hb9y16JvX5DBtit10cBOLcYgepBtjvGo87lN3CaLPG5sR5cXO%2FPzC6SsF8DzfFOiPM2%2F3Cpai0%3D%7Ctkp%3ABk9SR8LQuqOPYw

 

It's not efficient you're right, but it saves me using those ineffective 12V electric blankets, and my battery is 19.2Ah so there's plenty of juice. If I use too much, I'll simply fold my bike into a bus (origami black belt, the resulting bus will be substantially smaller than the bike). Also, it saves my buying 12V floodlights for night gardening.

 

p.s. This AliExpress sale is really good. I reckon they must have massively overstocked for Black Friday and Cyber Monday.

 

 

 

...but that "150 lumen" rear laser light won't look like this. I'd need to have bought two, for a start.

 

Edited December 18, 20232 yr by guerney

It doesn't make sense to use an inverter because you're double converting - say from 12v to 240v, then 240v to 36v. It's much simpler, cheeper and more efficient to use universal charge controller board or a step-up/down buck converter with current control.

https://www.ebay.co.uk/itm/392248280526?hash=item5b53d1c5ce:g:KBEAAOSwdLhb~mMo&amdata=enc%3AAQAIAAAA0PlT95LqwZya22a1UbK0oCuVz5jERR525T%2F8Ap7j9KRHVS1AAI3pnhRC2NoRLG71kbdMCfFcrgKABpiv%2FHHhMQ342tHWZFuQfgPmczG8199NVw7X%2FH2D0jvO750PazS2A0%2BSNE6bGFTRh70%2FhOstmBf0Cb1Pe4XchlW9ch9pz2Szc7RjY8CRiHO8IQkSxplTbhh%2FI5QR5Da00Hb9y16JvX5DBtit10cBOLcYgepBtjvGo87lN3CaLPG5sR5cXO%2FPzC6SsF8DzfFOiPM2%2F3Cpai0%3D%7Ctkp%3ABk9SR8LQuqOPYw

 

Weather is warming up so hope to be able to comfortably experiment again in a safe location. With regard to mobile charging of my 'recovered' lithium ion battery (no BMS, cell voltage monitoring) or other bike batteries, I have ordered a dc dc boost converter of the above type with the idea of charging my bike batteries away from a power supply using say my car battery booster (~15V lithium) or maybe a car battery. From what I've seen on Youtube this should work provided I am careful and set the right voltage and current levels. What do you think?

Weather is warming up so hope to be able to comfortably experiment again in a safe location. With regard to mobile charging of my 'recovered' lithium ion battery (no BMS, cell voltage monitoring) or other bike batteries, I have ordered a dc dc boost converter of the above type with the idea of charging my bike batteries away from a power supply using say my car battery booster (~15V lithium) or maybe a car battery. From what I've seen on Youtube this should work provided I am careful and set the right voltage and current levels. What do you think?

I use one for charging some of my 48v lithium batteries. For your first couple of charges, check with a voltmeter that it's working properly and cutting off at the right voltage.