Large Model Association Forum

Hi
I would appreciate some advise please
I have for years now used Sanyo Nicad batterys 4.8v for my RX and servos but find replacements no longer avaliable.
I have tryed NM Hydrids but find fast charging them a problem, getting false " fully charge " readings.I use a Schulze charger.
So i have decided to use li po batterys, which i thought would be quite straight forward,but it seems that is not the case.
I know nothing about lipos ( there are so many makes ) having only read all the bad things about them. I have tryed to find out just what i need to buy in the way of a voltage regulator and a cell balancer for the charger.With out much success. Getting much conflictind advise.
I have spoken to people how seem to have success just using a 2 cell lipo and no regulator also a lipo in the TX with out problems, but thats not what the radio manufactures recommend.
I use JR 519 servos, which show a fully stalled current draw of .08amps per servo, my model has 9 of them, and a 2500 ah battery.
Could some one please just tell me what i need to by to power my radio inacordance with the makes ( JR ) recommend ations. using a lipo a and also what cell balancer i need .

Hi,

I like you mourn the passing of the NIcad and have had some problems with 'false peaks' using NiMH batteries. I also use a Schulze charger.
I have found that the supply to the charger can influence performance and should be either a high quality, regulated, high current (10A or more ) mains supply or a minimum 20AH 6 cell lead acid battery. I have used both suuccessfully with the 4.8v NiMN cells I used for my sons Mardave race car ( discharge currents up to 15A!). These cells were VapexTech 4300mAH purchased from www.component-shop.co.uk and are not expensive. I also use the same set up for 2000mAH cells in a number of planes. Another point that may be of interest is that I always slow charge and cycle new packs before fast charging.

Dont give up on NiMH cells, after all you won't need regulators or balancing chargers with them. Li-Po's are fine if you need high capacity and light weight. But they do need care. The fire risk is real if mishandled, I have a friend who is no fool but a wrongly set charger resulted in a fire in his kitchen!

Hope this helps

Paul Scott

[quote="Paul Scott"...................
Dont give up on NiMH cells, after all you won't need regulators or balancing chargers with them. Li-Po's are fine if you need high capacity and light weight. But they do need care. The fire risk is real if mishandled, I have a friend who is no fool but a wrongly set charger resulted in a fire in his kitchen!

Hope this helps

Paul Scott[/quote]



I echo that Paul,
Arthur, can it be that you have not read, but more to the point implemented, the extensive NiMH charging recommendations Mr Schulze includes with all his chargers? (as indeed he does for all types of batteries).

Most peoples fix for false cutouts is to slow charge NiMH's but Mr Schulze says to always discharge first then charge at NO LESS than 1C, in doing so he says not to use the Auto facility for NiMH but set the rate manually.

I too used to get false cutouts before I implemented his recommendations now it's a thing of the past.
It can be a bit of a pain to always discharge first, particularly in the case of Rx/Tx packs if you use capacities miles over what you really need but that is the nub of his spiel, if you under use NiMH's they get lazy and play up.
This is borne out by the fact that you don't normally get false cutouts on well used power packs because the full capacity/cycle is normally always used and the battery doesn't have chance to get lazy, unless you store it for a long time (he covers that too).

The problem is that each and every battery technoligy is different so to change will need another learning curve to negotiate..........you takes your choice!

Whilst surfing the net for info on charging batteries, I came across this site http://batteryuniversity.com/
Some of the info may be known to those used to the weird and wonderful world of leccy flying, but I found it really helpful.

I wont be able to visit any of the fly-ins for the next few weeks as I have to sit in a pool bar drinking cold beer overlooking the Med!

Cheers
Steve

It all depends what size model you have as to what size pack and regulator you require. I always prefer to be slightly overkill here, mainly to allow for any amp draw spikes or current drains caused by any servo issues in flight.

For example:

A .50 size model with 4-5 standard size servos should be ok on a 5amp regulator and a 2s-1500mah+ lipo.
A .60-1.20 size model with 7-11 standard size servos would be better on a 8amp regulator and 2s-2200mah+ lipo.
A 50cc size model or a model with high torque servos may need more, here I use a 20amp regulator and 2 x 2s-2200mah in dual parallel outputs. This enables me to power both ends of my receiver so servos at one end don't drown those at the other. It is possible to use one pack, but I prefer the redundancy protection of dual packs.
Larger models such as 100cc upwards would be better on power distribution boards and dual bigger Rx packs.

Most the voltage regulators I've used in my models are switchable for output from 4.8/5v - 6v, so you can adjust to suit your receiver and servo requirements. If you're using newer high voltage brushless servos that run on 7.4v, then a direct feed from a 2s lipo can be ok, provided the receiver can take the voltage.

Many regulators can take an input voltage range, for example the 5amp ones I use from 4-max.co.uk are ok for an input from 2-6s, though I find they actually prefer 3-6s in reality. The 8amp one is set for 2-3s and works fine on either.

There is probably a good debate over 2s Rx packs versus 3s, as the 3s pack having a higher voltage will draw less current for the same power, so therefore needing a smaller capacity, though I've always gone 2s where possible. My personal reason being a slimmer battery is often easier to place in my models.

Hope that helps.