Charging Lipo from an inverter. Any expereince?

[handmadematt]

Hi chaps.
I've got a high power quality inverter in my camper van. It produces a modified sine wave, not pure.
I have four large leisure batteries and 390 watts of solar on the roof.
I successfully charged the SLA batteries on my ebike for weeks on end and wasn't too fussed about any outcome because the charger was a cheap one. No ill effects.
The new equipment that I am about to start playing with is a whole other story. It's rather more expensive so I don't want to damage anything with the modified sine wave.

It's a 14S 10Ah 58.8v lithium polymer 150A max discharge battery pack inc. 3.5A fan cooled charger
(What does the 14S bit mean by the way?)

"It has a balance BMS (Battery management system) built in. This monitors and balances each cell, and also offers short circuit, under voltage over voltage and over-temp protection.
The battery charger is the latest model which is CE certified and fully protected too, it's a true "smart" charger and much more sophisticated than most available. Besides all the normal safety features you would expect it will even detect a fault in the battery pack like high resistance."

It hasn't actually arrived yet so this is the best photo I have right now:

Any experiences or info would be much appreciated.
Many thanks.

 

[KirstinS]

Hi there - cant help you on the modified sine wave front I'm afraid. I'd have thought a quick email to the seller ought to give you an answer ?

I can tell you that 14s means 14 x 3.7v cells in series to get 51.8v (I presume 58.8v is just a typo). Litium cells are 3.7v nominal or 3.2v if Lifepo4

The most common ebike batteries are 36v (or 10s)

 

[handmadematt]

Thanks for the info. Unfortunately the seller said that he has no experience with inverters. He said that if it hums/ buzzes a lot and gets very hot then that could be an indicator of potential issues but it does sound vague.

(I'll ask him about the potential 58.8v typo, it could be that it is the charge voltage of the 51.8v pack?)

 

[KirstinS]

Ahh yes - normally the nominal voltage of the pack is referred to eg a 36v pack rather than the charge voltage (42v in the case of a 36v pack)

So yes your 51.8v (14s) nominal pack will have a charge voltage of 58.8v

 

[handmadematt]

I've found these links to what I think is the right product although there are some variants.

http://www.szgrn.com/Spec/L200-E.pdf

http://www.green-charger.com/Product/id-98/L200CM-48F-Smart-Car-Battery-Charger-for-51.2V-LiFePo4-Battery.html

http://www.green-charger.com/Product/id-44/L200CM-48-LiPo-Portable-13S-48V-Li-ion-Car-Battery-Charger.html

http://www.total-power-solution.com/index.php?route=product/product&product_id=95

If anyone can work out whether the unit will run with a modified sine unit from this data please let me know. Otherwise I'll have to splash out on a pure sine inverter which is money I'd rather not spend. It wouldn't need to be a large inverter which will help keep the cost down. I was thinking a 300w unit would be ideal.

 

[oigoi]

I have been using a charger like this http://www.eclipsebikes.com/lifepo4-battery-charger-p-1036.html on a modified sine wave inverter for several years now with no ill effects so I think you will be fine

 

[Kinninvie]

You simply need a 240 volt input for the charger.
It does not matter how you get the voltage,whether its from the mains or an inverter or from solar panels.

 

[SRS]

You simply need a 240 volt input for the charger.
It does not matter how you get the voltage,whether its from the mains or an inverter or from solar panels.

240v mains produces a clean sine wave.

A modified sine wave is as it says, modified. A rough representation, chopped about a bit if you like.

Some devices will run hot, others will not work at all. A good many devices don't care.

 

[Alan Quay]

You simply need a 240 volt input for the charger.
It does not matter how you get the voltage,whether its from the mains or an inverter or from solar panels.

The OP is asking whether his charger will work with a modified sign wave from an inverter.

I would guess yes. A modified sign wave is like a square wave, but with a short pause at 0v. This means that it sort of behaves a bit like a sine, in that there is a time period from max + to max - volts.
It won't be the same (10ms@50hz) though.

The input stage of your charger is likely to be a transformer and bridge rectifier. The Tx might not run as efficiently with modified square wave, but the rectifier won't care. From there on its all DC.

If you do try it, keep an eye/finger on it to check it doesn't get too hot.

I always think it a shame that we have to convert everything from n volts DC up to 240 AC, and back again. If you think about it, it's only because 240/220 AC is the standard.

Perhaps you would be better off with a charger that runs off DC, like the IMax ones? No inverter required.

http://pages.ebay.com/link/?nav=item.view&id=190818527250&alt=web

 

[handmadematt]

Perhaps you would be better off with a charger that runs off DC, like the IMax ones? No inverter required.
http://pages.ebay.com/link/?nav=item.view&id=190818527250&alt=web

I do like the look of that. Cheap too. However it states
"Can charge 6 cells LiPo battery." Mine is 14 cells right?

I'm with you on this converting DC to AC and back again being very inefficient.

Most of these DC charges tend to be for RC or Airsoft batteries, charging much smaller packs at a much slower rate than ebike packs. Correct me if I'm wrong.

 

[Deleted member 4366]

You'd nee 3 imax chargers or chare in three stages. One other thing: You battery is approximately 600wh, which means you need 50Ah at 12v to charge it. Add on inefficiency in the inverter and charger, and that will increase to 75 or 80aH. You shouldn't discharge a lead battery past half way, so you need at least 160Ah of good lead batteries for one charge. If your batteries are old or knackered, you need more.

 

[handmadematt]

Your battery is approximately 600wh

I thought it was 518 watt hours.

You need at least 160Ah of good lead batteries for one charge.

I have 12v 310Ah of Yuasa batteries in the camper, with the 390w of solar on top of that charging should be a doddle, especially in the daytime on a bright day.

 

[handmadematt]

This is what I'm trying to replace. I've never used it for more than ten or twenty mile trips at a time. Hopefully I'll also save a fortune on fuel, tax and insurance not to mention weight and "faff time."

 

[handmadematt]

You'd nee 3 imax chargers or charge in three stages.

For this reason I think I'll go down the inverter route and just deal with the inefficiencies. Inverters are great because they serve so many devices. Out of interest though, how would one wire up three charges to charge one bulk pack? Also, to charge in three stages would that mean opening up the pack to isolate 5 cells at a time? (4 cells for the third charge.) If one does this what happens about BMS?
Thanks again mate.

 

[Deleted member 4366]

You'd need to splice in some extra wires and connectors to the balance wires, then charge 5S, 5S and 4S. The charger will do the balancing.

 

[oigoi]

240v mains produces a clean sine wave.

A modified sine wave is as it says, modified. A rough representation, chopped about a bit if you like.

Some devices will run hot, others will not work at all. A good many devices don't care.

Agree, I have found most things work fine, however so far I have found two things that do not. The charger on my electric toothbrush died immediately and an old dell desktop pc died too

 

[handmadematt]

The charger on my electric toothbrush died immediately

This is my concern.

 

[handmadematt]

The charger will do the balancing.

Thank you. I'm learning lots here. Are the following statements correct?

• The BMS that is fitted to the battery pack solely protects from damagingly deep discharge.
• The BMS fitted to the battery pack plays no role in limiting charge (I have read charging to 90% capacity will drastically increase available charge cycles. (It's so different to SLA which I am familiar with.) This would be the job of a charger.
• Splicing in extra connectors to the balancing wires to charge the cells (5S/ 5S/ 4S) will bypass the BMS. (To no ill effect?)

My options are as follows in rough order of financial appeal:

1. Experiment and hope for the best using my existing modified sine inverter.
2. Buy an DC charger and charge in three stages.
3. Buy a 300w pure sine wave inverter.
4. Buy three imax chargers.

What would you do?

(I just want to iterate that I am not worried by any of this, nor am I stressing out. I am just interested, keen to learn and love talking about these things. )

 

[oigoi]

Thank you. I'm learning lots here. Are the following statements correct?

• The BMS that is fitted to the battery pack solely protects from damagingly deep discharge.
• The BMS fitted to the battery pack plays no role in limiting charge (I have read charging to 90% capacity will drastically increase available charge cycles. (It's so different to SLA which I am familiar with.) This would be the job of a charger.
• Splicing in extra connectors to the balancing wires to charge the cells (5S/ 5S/ 4S) will bypass the BMS. (To no ill effect?)

My options are as follows in rough order of financial appeal:

1. Experiment and hope for the best using my existing modified sine inverter.
2. Buy an DC charger and charge in three stages.
3. Buy a 300w pure sine wave inverter.
4. Buy three imax chargers.

What would you do?

(I just want to iterate that I am not worried by any of this, nor am I stressing out. I am just interested, keen to learn and love talking about these things. )

It is most likely that, as Mike Higgins suggested above, the first parts of the charger's circuit inside are a transformer and rectifier turning the ac into dc. It therefore does not matter if the ac is a modified sine wave. My toothbrush charger died because it did not convert the power to dc immediately, parts of the circuit tried using the modified sine wave which can have some voltage spikes on it (interesting to look at on an oscilloscope) and that was too much for it.

 

[handmadematt]

Interesting stuff guys.
So I've wanted to get a pure sine wave inverter anyway for a while so I went ahead and did it. I bought a 300 watt unit made by Sterling, PN: SIB12300. Very good equipment on the whole so I have no doubts about the unit.

What happens is very strange.
When charging the bike from this new unit the chargers fan never runs and the Cycle Analyst never shows charging to be above 30 - 40 watts. When I try with the mains grid power I'm getting a full fan and 185 watts showing. The weird thing is it also works completely fine with my modified sine wave inverter which I was concerned about in the beginning.
Modified sine inverter = full 185 watt charge
Any ideas what's going on?