Don't forget to check your spam folder if you don't get an activation email after joining!!

Field charging

Discussion about Tx, Rx, Servo's, Batteries, Chargers, and all the other things we like to talk about..
Moderator: VinceC
MDev
Posts: 155
Joined: 07 Oct 2018, 19:17
Location: WEYMOUTH

Field charging

Post by MDev »

I’m looking at using a life type or similar battery pack as a charging pack in the field, there are a few brands to choose from nowadays. The larger of the battery sizes I use are 2 X 3S 5000mah or 4S 4200mah and being able to recharge a few times a day, I will replace the amount used in the power bank via a 220v mains input at the end of the day.
Any suggestions or advice gratefully received, electrical advice needs to be wrapped in understandable forms 😛. Using noisy smelly generators, cans of petrol and heavy lead acid batteries might be a thing of the past?
Thanks
Mark
Phill Tadman
Posts: 331
Joined: 18 Aug 2015, 20:38
Location: South Cambs

Re: Field charging

Post by Phill Tadman »

Hey Mark,

I too would be interested in solutions.

My van 110 AH leisure battery can only recharge my FES twin 5000 mAH batteries 3 or 4 times at the field before the load drops the supplied voltage and my lipo charger complains.

I was thinking of using a suitcase generator.

Phill
MDev
Posts: 155
Joined: 07 Oct 2018, 19:17
Location: WEYMOUTH

Re: Field charging

Post by MDev »

Hi Phil, I have a small Ipax Genny from Screwfix, the 12v output isn’t worth using so I plug a 220v power supply in to get 12v to my chargers, the charging times are not quick, go any larger and the price goes up substantially and you have to keep an eye on things to change the batteries , top up fuel etc and then only when it’s dry. Put the genny in the car with madam would not be appreciated, which should I leave at home? 😂

I was looking at the Ecoflow 200 (288w) but equating the quoted figures to real life use is difficult.

M
MDev
Posts: 155
Joined: 07 Oct 2018, 19:17
Location: WEYMOUTH

Re: Field charging

Post by MDev »

I’ve just come across a life battery, 1500W and 15kg. Food for thought?
M
Attachments
900A9D8F-8E0B-4F6E-8E7D-7B54BA2CE98F.png
User avatar
Peter Balcombe
Posts: 1329
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: Field charging

Post by Peter Balcombe »

Quite expensive though Mark :(
However, it does appear that the quiet battery based power units tend to be more expensive than the noisier ‘Genny’ type solutions.
It did occur to me that you need a fair amount of power capacity for 6S 5000mAH size pack charging capability as roughly 25V x 5000mAH equates to 125WH/charge if a full charge is needed.

I suspect that the power pack WH quoted is the internal battery capacity. You are likely to lose some of that in the output voltage conversion where applicable, plus some power lost (as heat generated) in the model pack charger.

Also note (if not already aware) that your model pack charger input current will be higher than the battery charge rate if charging >3S due to the need for the charger to step up the voltage. (Watts in cannot be less than Watts out) Thus a 6S charge will draw just over twice the battery charge current from a nominal 12v charger input supply, whereas a 3S charge will draw roughly the same.
harry curzon
Posts: 120
Joined: 21 Jul 2018, 09:32
Location: Gloucestershire

Re: Field charging

Post by harry curzon »

Start with some assumptions -
Your recharge source is 12-14 V
You discharge your lipos by 80% so that is what needs to be put back in.

In that case the 2x3S 5000 will need around 8Ah per charge, and the 4S 4200 will need around 4.5Ah per charge. Be cautious and allow an extra 20% for losses in the system. So allow for the source to need 10Ah and 5.5Ah respectively.
If you want 5 charges of the 2x3S, then the source needs to be able to give around 5 x 10Ah = 50Ah. You will need a source in excess of that, it isn't going to give you 10 amps to recharge your 2x3S 5000s when it is substantially discharged!

That might sound ok versus a leisure battery of 70Ah but it could well be hitting your charger's input low Voltage cut out before you get 50 Ah out of it, and that's when it is brand new. Soon the charger will be cutting out long before you have had anything like the Ah claimed on the battery's label. Rule of thumb, they lose half of their effective capacity in just 2 years even with little use, it is just chemical ageing. So you end up buying a ridiculously big Ah and weight which is wasted in its early days, just to have it keep working through the 1 - 4 year old stage. And then buy a replacement probably after just 2 or 3 years.

Alternatives -
Buy enough lipos to last the day and charge them all at home.
Buy a petrol generator.
Buy a LiFePo leisure battery. They are a fraction of the weight of a lead acid leisure. They keep their V until nearly completely discharged. They normally have electronics built in to protect from over charge and over discharge. They are very expensive. They claim a 10 year life, that remains to be seen, but if so they are no more expensive than lead acid leisure over a 10 yr period.

I have gone down the LiFePo route but only this last year so cannot say if the longevity claims will stand up
SP250
Posts: 170
Joined: 18 Mar 2015, 06:19
Location: North Shropshire

Re: Field charging

Post by SP250 »

Succinctly put Harry - I'll stick with the petrol generator option as I already have a couple to choose from and an ex motorhome lead acid leisure battery which does do a few 3s Lipo charges at the field but then runs out of steam.

John M
MDev
Posts: 155
Joined: 07 Oct 2018, 19:17
Location: WEYMOUTH

Re: Field charging

Post by MDev »

I suppose that what I should take from all this is that the market is changing but it’s not quite ready yet to cater for what we need?
I have a few weeks before I need to do anything so I’ll keep an open mind.
Cheers
M
Post Reply