Battery to battery charging

Batteries, Chargers, and Battery Management Systems.
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j bjork   10 kW

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Battery to battery charging

Post by j bjork » Jan 03 2021 6:26am

I want to be able to do some fast charging out in the field when taking a brake, to be able to get an extra lap or two.
I have 22s 50Ah on the bike, that I charge to 90V.
The plan is to use a 12s 70Ah charged to around 49V to charge it with.
I want to charge with up to 50A, or at least close to that.

Would it work to parallel 3-4 of these: https://www.aliexpress.com/item/1005001 ... hweb201603_

Or maybe 2-3 of these: https://www.aliexpress.com/item/3303425 ... 07825975.4

What do you think, or maybe there is a better option?

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jonescg   1.21 GW

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Re: Battery to battery charging

Post by jonescg » Jan 03 2021 7:14am

So you'd carry a battery with you on your ride? It only makes sense to fast charge it from another battery if you can't remove the battery and swap it with a fully charged one.

Then there's the BMS issue - if you have a FET based BMS it might not like the high charge rate.

But, technically you can put a battery of higher voltage in parallel with the flat battery and let them settle out. About 4 V difference might be enough to drive a decent current for a while.

j bjork   10 kW

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Re: Battery to battery charging

Post by j bjork » Jan 03 2021 7:41am

As it is now the battery is not removable on the bike, and I dont have the cells to build an extra one atm anyway.
I will have all the extra stuff in the car or on the trailer, so the plan is to take a 20-30 min brake (that I would probably do anyway) and in that time charge the battery.

The bms can take 50A charging, a few seconds over that is ok.
The batteries I plan to use for charging is two 12s modules , so I guess I can connect them to 24s. But they are not equal, so I am not sure how well that would work.
And it would be limited how much I would get out of them before the voltages even out I guess, well it depends of the charge level when I start of course.

But if I just connect them together I think the current would be way to high at first? I probably would have to limit current somehow anyway.

Edit, it seems I can set the bms up to 150A. But I am not so sure about charging the cells over 1C, I think 50A will be fast enough anyway.

john61ct   100 GW

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Re: Battery to battery charging

Post by john61ct » Jan 03 2021 12:15pm

Figure cheap chinese DCDCs can only handle half of what even the fine print says, and order lots if spares.

No mains anywhere around?

No car with an old-fashioned alternator?

Charging from storage is just so inefficient, also wearing out two packs not just one.

If you use a DC-input charger anyway, just put enough cheap 60lb FLA 6V units together to feed it.

Or a mains charger running off a little inverter genset, can find for only $3-400

You really want a solution that auto terminates charging!

But if you do go with those cheap Chinese, make sure they have good current limiting not just current protection

ideally adjustable current level.

The Vicor DCDC modules can go super cheap on eBay, really top quality but will require more DIY fiddling

Hillhater   100 GW

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Re: Battery to battery charging

Post by Hillhater » Jan 03 2021 10:49pm

j bjork wrote:
Jan 03 2021 6:26am
I want to be able to do some fast charging out in the field when taking a brake, to be able to get an extra lap or two.
I have 22s 50Ah on the bike, that I charge to 90V.
The plan is to use a 12s 70Ah charged to around 49V to charge it with.
I want to charge with up to 50A, or at least close to that.
I suspect you are looking for a ideal solution that does not exist.
To “up volt”. 48v to 90v at 50 amps is big ask, especially ina portable package.
That is a 4.5kW DC/DC charger ! :shock:
Maybe somthing like those solar charge controllers migh do it , but not at those current levels
I have one that would cover the voltage requirements, but only at 10 A ...(MPT 7210A)
This forum owes its existence to Justin of ebikes.ca

j bjork   10 kW

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Re: Battery to battery charging

Post by j bjork » Jan 05 2021 5:40am

Here are the specs for the first ones i linked:

900W 15A Digital Display DC-DC Boost Converter 8-60V to 10-120V Constant Current Voltage CC CV Step Up Module
Specification:
Input voltage (U-IN): DC 8V~60V
Input current: 0~15A
Output voltage (U-OUT): 10V~120V
Output current: 0~15A
Conversion efficiency: 85%
Working frequency: 150kHz
Short circuit protection: 20A fuse (non-self-recovery)
Working temperature: -40℃~+85℃
Control method: digital control + LCD screen display
Voltage adjustment display: 0.00V~00.0V~000V
Current adjustment display: 0.00A~00.0A
Output ripple: ≤50mV
Storeable array: 10 groups
Net weight: 213g
Product size: 48mmx100mmx110mm/1.89x3.94x4.33"
Packing size: 90mmx110mmx120mm/3.54x4.33x4.72"
Gross weight: 267g

Instruction:
1. Start boost
Manual boosting press and hold the OK button for 10 seconds to enter the interface and select AUTO-OFF as manual boosting. , Select AUTO-ON to automatically start the boost.
Click OK to start or stop the boost.
2. Set storage
In the setting mode, long press the SET button for 10 seconds to enter the data storage interface, and use the up and down keys to select 10 groups of data from 0 to 9, and press the SET button to save the settings.
3. Retrieve and access the array
In the normal interface, press and hold the SET button for 10 seconds to enter the storage and recall interface. You can select 10 data groups from 0 to 9 through the up and down keys, and press the SET button to confirm the recall.

Note:
1. There may be slight size deviations due to manual measurement, different measuring methods and tools.
2. The picture may not reflect the actual color of the item because of different photographing light, angle and display monitor.

As it says it does CC and CV, and "voltage adjustment display" "current adjustment display" I assume it should be possible to adjust V and A?

The second one:

This is a non-isolated DC power converter module with long service life.
High power and stable output, it converts 10-60VDC to 12-97VDC.
High quality components ensures high conversion efficiency, up to 97%.
Designed with smart temperature control fan, which will automatically work when temperature reaches about 60℃, and stop when temperature drops below 60℃.
Widely used for high power solar street lamp driving, various LED lighting CV driving, vehicle-mounted and mobile device power supply, DIY adjustable CV CC power supply, solar power charging, and various batteries charging.


Specification:
Name: 1500W step up constant current module
Type: Non-isolated step-up module (BOOST)
Input Voltage: DC10V to 60V
Input Current: 10V-30V input voltage, maximum current is 35A-40A; 31-60V input voltage, maximum current is 30A-35A
Quiescent Current: 15mA(when convert 12V to 20V, higher output voltage will increase quiescent current)
Output Voltage: 12-97V continuously adjustable (cannot be used to step down voltage)
Output Current: 22A (related to the input and output voltage difference, the greater voltage difference is, the smaller output current will be. please enhance heat dissipation when current is over 15A)
Constant Current Range: 0.8-22A(+/-0.3A)
Reverse Input Protection: Yes (150A power MOS reverse protection)
Input Low Voltage Protection: Yes (10V-50V adjustable, self-recovery)
Operating Temperature: -40℃ to 85℃(if temperature is too high, please enhance heat dissipation)
Frequency: 150KHz
Conversion Efficiency: 92% to 97% (Efficiency is related to input/output voltage, current and voltage difference. The smaller difference is, the higher efficiency will be)
Input Over Current Protection: Yes (automatically protect when input is more than 40A, and power supply voltage will not increase)
Short Circuit Protection: Yes (input 60A fuse) please operate carefully, try not to cause short circuit.
Reverse Input Protection: Yes ((150A power MOS tube, can be connected reversely for long time)
Installation Method: Four 3mm standoffs
Wiring Method: Terminal blocks (Please use large current copper wire)
Output Power: Max. Output Power = Input Voltage*30A(If input 12V, the max output power=12V*30A = 360W)
(If input 24V, the max output power=24V*30A = 720W)

Weight: 372g / 13.1oz (approx.)



Package list:
1 * Module



Instructions:
Module output should not short circuit or measure current directly with multimeter short circuit, short circuit will burn out module.
Under voltage adjustable range:DC10V-50V (clockwise to increase, counterclockwise to reduce), firstly adjust under-voltage to the minimum, then adjust input voltage to required under-voltage protection value, slowly adjust under-voltage value clockwise to increase; when the under-voltage light is on, adjust counterclockwise of one circle, then power on again.
Input under-voltage protection mainly used to prevent battery from over-discharging when input power source is battery. Low battery voltage will damage power module and battery. When input is switching power supply, it also need to set the low voltage protection.
Constant voltage adjustable range:DC12-97V(clockwise to increase, counterclockwise to reduce), first adjust voltage to the required voltage and then connected to the load.
Constant current adjustable range:0.8-22A (clockwise to increase and counterclockwise to reduce), first disconnect load, then adjust output voltage to required voltage, adjust current to the minimum (counterclockwise turn CC potentiometer about 30 circles), connect an ammeter in series to the output, then slowly adjust current.(booster module cannot directly adjust current by short circuit)
Input voltage should not be lower than 10V or higher than 60V, (when input voltage is lower than 12V, please properly reduce the load).
Make sure the input voltage is at lease 2V lower than output voltage.
If use switching power supply or other secondary power supply, please make sure that power is 1.3 times greater or more than the power supply module's power.
During over current or under-voltage protection, output will still have voltage that is close to the input voltage, protection means no boosting voltage.

Both says you can adjust V and A.

j bjork   10 kW

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Re: Battery to battery charging

Post by j bjork » Jan 05 2021 5:50am

john61ct wrote:
Jan 03 2021 12:15pm
Figure cheap chinese DCDCs can only handle half of what even the fine print says, and order lots if spares.

No mains anywhere around? (No, and if there are they are not available during practice.)

No car with an old-fashioned alternator? (Sure, but to do what? Should I series connect a bunch of them?)

Charging from storage is just so inefficient, also wearing out two packs not just one.

If you use a DC-input charger anyway, just put enough cheap 60lb FLA 6V units together to feed it. (Why should I buy a bunch of lead acids? What is better with using those than the batteries I already have?)

Or a mains charger running off a little inverter genset, can find for only $3-400 (please link one of those, I have only seen expensive ones that can do 5kw. And my charger can only use 2 phases, (or one)I wonder how the 3 phase generators like that?)

You really want a solution that auto terminates charging! (Why? I will only use it when I am around anyway. If it comes close to full voltage there will be very low amps)

But if you do go with those cheap Chinese, make sure they have good current limiting not just current protection

ideally adjustable current level. (From what I understand both have that)

The Vicor DCDC modules can go super cheap on eBay, really top quality but will require more DIY fiddling ( I will have a look and see what it is)
My reply in ( )

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fechter   100 GW

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Re: Battery to battery charging

Post by fechter » Jan 05 2021 9:23am

You can adjust the output voltage of the dc-dc to prevent overcharging and those have current limiting, so should work OK.
As John pointed out, the specifications on those tend to be exaggerated so don't try to run them at the max "rating" for very long. Best to run them closer to 50% of their rating.
Use a fan on the dc-dc converters. Even a small fan will help a lot with the heating issue.
Use fuses on each converter in case one decides to blow up.

I've seen a few setups like this that worked well. Typical alternative is a stinky, noisy, gas generator. There will be quite a bit of loss, so don't expect to get all the energy from one pack to the other.
"One test is worth a thousand opinions"

john61ct   100 GW

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Re: Battery to battery charging

Post by john61ct » Jan 05 2021 12:42pm

Maybe Sweden does not have portable inverter generators?

Honda EU2200i about $1200?

In every USIAN hardware retail and big box, cheap knockoffs that aren't as long lived, but all are like a carry-on bag sized, near silent and fuel efficient, and under half the price.

I guess if you want 240V those are bigger and pricey, but still 2-phase

better IMO to stick to small 120V and get a mains charger to match, Satiators stacked for example.

With a good alternator setup and DCDC charger could go to 24V output maybe 30-50A

Use that as input to a DCDC charger or converter.

If you use batteries to feed them, you will need a source set much larger than the target pack, again wastes a lot of energy, and you are doing double the cycling wear and tear.

Deep cycling lead is cheap for source, say $1/Ah @12V here.

but NP if you have lots of LI you are willing to sacrifice.

At least put in an HVC to auto terminate, very fire-risky otherwise!

j bjork   10 kW

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Re: Battery to battery charging

Post by j bjork » Jan 05 2021 2:17pm

Thanks fechter, that was the answer I was looking for.
I was mostly worried if there would be a problem with paralleling them.
They have fans, but it is probably a good idea to make a duct under the cooling fins and mount bigger ones.

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fechter   100 GW

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Re: Battery to battery charging

Post by fechter » Jan 05 2021 10:53pm

Parallel should be OK for identical units. You'd want to dial in the voltage of each one separately before paralleling the outputs. If one is off a little, it won't matter.

Another setup I've seen is to just use a big 12v - 120vac inverter on a car (or truck) and run the engine while charging. Probably won't get nearly as much power though.
"One test is worth a thousand opinions"

john61ct   100 GW

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Re: Battery to battery charging

Post by john61ct » Jan 06 2021 12:03am

Depends on the truck.

Met a guy had an expo truck fitted with a surplus ex-Hummer alternator rated 500+ amps continuous in the hot desert, and that was at 28V

Only cost $250, the custom external regulator, mounts, pulleys etc over triple that,

but he could power a village from his 900+ Ah LFP bank

normally high-idling a couple hours a week was plenty for just his needs, full electric galley, HWS and all.

Such vehicles are likely illegal for civilians to own in Sweden though

Nixunen   100 mW

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Re: Battery to battery charging

Post by Nixunen » Jan 06 2021 3:08am

Just change your motor controller to Nucular controller. It support charge trough controller and use motor as a coil. So you can feed power from another dc source. Even at another battery to charge your bike battery. I done it many times. I had another battery (52v) at my backbag and i use it to charge my bike battery 72v (84v at full). It work really well.

j bjork   10 kW

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Re: Battery to battery charging

Post by j bjork » Jan 06 2021 7:47am

I have a nuc 24fet, (not on this bike) nice controller but not powerful enough.
It is a nice feature, but it heats up both motor and controller.
So not very good if you want to ride hard right after charging.

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