Dc dc charging e bike

[SandraL]

Thinking that rather than using inverter to get 240 vac and then charging brick to go to 42 vdc it may be better to just have one dc dc charger.



Anyone like to comment on this from ebay, i think you can set output voltage and current, for my 36v battery thinking of 41.5 v and 2 amp output. So my 8.8ah batt would need max of 4 hours assuming not fully discharged. Supplied charger is 42v but I understand charging to a slightly lower voltage gives longer life at small loss of capacity.

Your thoughts please.

 

[tonyidle]

If you can arrange for its output to exactly mirror that of the supplied charger it will work well. Current limit should be set to that of he original charger as well as voltage.

 

[LesW]

Looks interesting.

 

[SandraL]

If you can arrange for its output to exactly mirror that of the supplied charger it will work well. Current limit should be set to that of he original charger as well as voltage.

Yes, original charger is 2a output and 42v.

 

[hilldweller]

Your thoughts please.

It's just a voltage booster not a Lion charger - it may well work if set correctly but the life of your £200-400 battery is at stake.

There are "proper job" chargers for RC models that run off 12V but not that cheap.

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[SuperMike]

Indeed, that is a power supply type bit of kit. Definitely not any sort of charger. Simple words, do not use.

 

[SandraL]

Agreed it is a voltage booster.
My thoughts are to set boost volts to 41v. This is 1 volt under the proper charger.
Set max output current to 2 amps, same as original charger.
It will not be left on overnight, no long charges.

If , big if, it can be set accurately as advert suggests, not left on for extended periods then Im tempted to try one.

 

[andy63]

Thanks for the link... worth a try for that money..
Andy

 

[Minxy]

What concerns me about this is the amount of time it will be running to provide sufficient charge back into the battery, not to mention the possible damage it could cause if it doesn't perform correctly .. is it really worth risking having to buy a new battery? It may be cheap but if it was so easy to do it this way don't you think that electric bike sellers would already have done it and be selling them at MH shows as a way to charge bikes from 12v?

 

[SandraL]

Re the amount of time to charge, this will be the same as original charger as both provide 2 amps.
Re cost , there are a few extra bits required, box, cable, plugs, fuse etc but I guess total about £25 to £30.
If it goes wrong then possibly will cause problems or damage. But by reducing charging voltage by one volt I have a margin of safety against overcharging.
For myself I like playing with these bits and am happy to accept the risks.

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[andy63]

bike sellers would already have done it and be selling them at MH shows as a way to charge bikes from 12v?

I suspect in the scheme of things they don' look at that market as been worth bothering with... might change
Andy

 

[hilldweller]

If it goes wrong then possibly will cause problems or damage.

Volts are on your side here, since it boosts voltage there is a good chance if it goes tits up the voltage would end up 12V max.

I would suggest charging via a diode in case it does fail and tries to totally discharge your battery, which should be protected but you never know.

 

[stevec]

I wouldn't use. Lithium ion batteries require a very particular charge profile. Part constant current, part constant voltage. This one doesn't do that. As others have said it's not worth risking your expensive batteries.

 

[SandraL]

http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

Link has info re charging batts, mine are 18650 cells.


Ok, its a bit simplistic but as I read it, keep voltage within limits ( 41v is 1 volt under standard charger)
Keep current within limits, ( original is 2a max, same as I propose)
Do not leave on too long, do not go overvolts.
Current to decrease as you get to fully charged, as max volts from "charger" is set at 41v, when batt gets to 41v current will decrease to zero.

Re suggestion to add diode to prevent bike battery discharging , excellen idea, thanks.

Thanks for all the comments.

 

[hilldweller]

http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries.

A good site for lead acid data too.

A good/frightening read. I used to fly model helicopters, the magazines on them regularly featured cars on fire form charging batteries via the car battery at the flying field. The batteries used usually did not have built in protection so were at the mercy of the charger. I don't know how the insurance companies went on to a claim of "I set fire to my car charging my helicopter battery" and I wonder what their reaction to "sorry my MH caught fire" would be.

As you almost certainly know, 18650s may or may not have internal protection.

Just for "fun" I "played around" with a poorly Lion battery off wife's bike. I was amazed at the complexity of the protection board inside. But to see what happens I shorted out a cell, this in a dying battery, and found the flames quite spectacular.

The Boeing Dreamliner was grounded for a while after it's Lion batteries caught fire and we all know of phones etc spontaneously combusting.

I still have my Lithium Bag, a fireproof battery bag for carrying model batteries in.

Have FUN.

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[LesW]

The message I'm getting here is, don't bother with expensive Lithium batteries...

 

[hilldweller]

The message I'm getting here is, don't bother with expensive Lithium batteries...

The world will collapse without lithium batteries. Just treat them properly.

I had an battery drill lose it's NiMH batteries that weight a tonne. I put in two of my aircraft batteries, the drill weighed nothing, the charge lasted almost forever but I had to use the model aircraft charger to charge them.

I don't know who you are or where you are but you surely are surrounded by lithium and arachnids.

 

[SuperMike]

http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

Link has info re charging batts, mine are 18650 cells.


Ok, its a bit simplistic but as I read it, keep voltage within limits ( 41v is 1 volt under standard charger)
Keep current within limits, ( original is 2a max, same as I propose)
Do not leave on too long, do not go overvolts.
Current to decrease as you get to fully charged, as max volts from "charger" is set at 41v, when batt gets to 41v current will decrease to zero..

I think, I think, I think, that the eBay item you listed, being only a power supply, has no intelligence and thus will continue to push whatever you set the current for even when the cell reaches fully charged, and there lies the problem. The cell could go phut unless you constantly monitor what is going on. I think.

Please Sandra, except that this is not criticism merely a thought. I love fiddling and trying to do the impossible. I spent some of my working life at the Post Office (BT) research station where we pushed the boundaries constantly. My dad, god rest his soul, always said of me “ He is never happier than when he has a bit of wire “, but you are walking a course that risks damage to a very expensive item. Yes it might work, but then it might not, please be careful.

 

[Lenny HB]

I wouldn't use. Lithium ion batteries require a very particular charge profile. Part constant current, part constant voltage. This one doesn't do that. As others have said it's not worth risking your expensive batteries.

Totaly agree with bike batteries at 500 quid a pop not worth the risk. Also the bike batteries have electroics built into them that monitor the charge and give feedback to the charger so it would be unlikely to work anyway. Easier to charge from a pure sine inverter.

 

[SandraL]

YesI do appreciate the feed back.
Van showing no discharge.
Today connected my inverter, van meter shows -0.5a
Connected bike charger to inverter, now -1.5a
Connected bike batteryto charger, now -11.5a

This reduced over next 10 mins to -8.8a.

So bike charger puts in more than 2a at 36 v initially.?? Ie about 6amps at 12 volts.

Re constant current, if volts are fixed at 41v, and current at 2amps, then as battery volts rise the current will decrease. If the curent is to remain at 2amps then the charger volts will need to rise to maintain that 2amps.
As the voltage is fixed at 41v, current is not fixed. As I see it current is limited to 2amps max, and will decrease as batt
volts rises.
So it seems to me there are some significant losses using the inverter and charger of about 1.5amps or about 20 watts.
Insignificant if on mains hookup or if charging when driving. But if off hookup for a time i think still worth exploring at my own risk.

Edit. Just checked and connecter from charger to battery is just 2 wires, no extra signal wire as I have seen on some laptop chargers.

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[SuperMike]

Worth a read ...........................

http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

 

[tonyidle]

It's just a voltage booster not a Lion charger - it may well work if set correctly but the life of your £200-400 battery is at stake.

There are "proper job" chargers for RC models that run off 12V but not that cheap.

It depends on where the battery balancing circuit is placed. The RC-type batteries are just that - batteries- and the smart circuitry is in the charger which has a 4-wire (for a nominally 12v battery) connection. Where weight is not a major issue the smart stuff is built into the battery and the charger simply provides a fixed voltage (as in the case of electric bikes, wheelchairs, and scooters). Any device that outputs the same voltage and has a similar or higher current capability will be perfectly safe.