I have a 4.8 volt 2000mah NIMH recever battery on the ignition of a DLE 30 engine. Being new to gas and not very battery savy what's the minium safe voltage to fly before recharging.
Thanks,
Rich

Different battery cell types from different manufactures have different discharge profiles. I would cycle the battery and watch the the voltage drop and make note of the Ma's discharged on the charger as the battery  gets closer to the bottom. The Rcexl ignition draws about 500 ma at WOT and will work reliably at voltages of about 4.5 volts or a little less while under load. The older versions of the Rcexl ignitions will work down to 3.5 volts before they start cutting out at high RPM.

Just using an arbitrary voltage number is not the best way to judge whether a battery is safe to fly or not unless you are familiar with the specific battery. I would also strongly caution against following any individuals advice on a voltage number on any forum as there are many different battery types in use as ignition batteries.

Cycle your battery a few times and learn it's discharge characteristics, don't fly if your battery is at a level of discharge that won't hold at least 4.7 volts for about 20 minutes with a 500 ma load.

Thanks Jody, appreciate the quick response.<div>Rich</div>

I'd opt for a LiFePO4 through a diode or BEC to drop the voltage under 6V. They're not as unreliable as NiMH cells under load.

Sanyo eneloop 4 cell AA pack (NiMh type) is a reliable power source for RCEXL ignitions, also under load.

Regards

If the throttle is advanced and the engine does not rev-up, the voltage of the ignition battery could be too low or the pack could have a bad cell. That is what I found with my gasser.

The bottom line is that the ignition battery is as important as the glow plug for the glow engines. Always make sure it is in good shape and charged. Make a note on the number of flights you can have with a full charge and always charge the pack when that number is reached.

Measured the amps with 85% charged Turnigy pack. The draw is at 86A at full throttle.

86 amps?

Sorry Tim but with the utmost respect, that is nonsense. Where does this keep coming from?

1. An Rcexl ignition places very little load on the battery (200 - 400mAh) where the rated discharge current of NiMh (Eneloop) cells is in excess of 10C
2. It has been established more times than I care to remember, a 4-cell NiMh (Eneloop) battery is probably an optimum power source for these ignitions. They typically have a capacity of 2,000 - 2,300mAh which easily gives you 4 - 5 hours run time at wide open throttle
3. Running at 6V only increases the power consumption of the ignition (therefore heat dissipation) but doesn't give any better spark (these are digital devices)
4. I fail to see how it can be of an advantage to use a battery with nominal cell voltage above the safe operating voltage of the ignition and then use a semiconductor to drop the same voltage down to a save (yet marginal) level

If I had a dollar for every time I have seen this have to be explained, I'd be better off than I'm now

Here's a real simple answer. If you have a 4.8v battery a very safe place to stop using it will be at 4.8v. That will work every time. Why people seem to think they should take batteries below nominal voltage is beyond me.

mpascual, I just bought a 4 pack of Sanyo eneloop batteries. What is the best way to charge them.? I guess I should have asked that at the Toledo RC Expo! Thanks Capt,n

Slow. 1/2C.

Some Transmitters will warn when the voltage gets below 8.8 volts. That is 1.1 volt per cell for a 8 cell pac. Seems like 4.4 would be absolute low voltage discharge...but safe.

But what's the true voltage under load?

Stop at 4.8v., recharge before next days flying and really be safe!

And on a 4-cell Eneloop pack, you will reach that point after 4 - 5 hours of constant running
If people want "gadgets", there are the old fashioned battery indicators that start green (at fully charged), go yellow at around 5V and then red once the pack reaches 4.8V

Measure the current draw in a typical flight and multiple it by N. Make sure the total is less then 50% of the battery capacity. N is the number of flights u can have before recharge.

No guess work is necessary this way.

Question....what if you do not have a way to measure the current drawn by a typical flight?????

Some cells will reverse polarity or experience other damage when cell voltage gets too low. My earlier point is people have an ignition designed and intended to be run on minimum specified voltages. It may be 4.8v, 6v, or 7.2v. Doesn't matter. Why, and I'll repeat that, why, would anyone have a need to run their ignitions at voltages less that specified by the manufacturer? Are modelers today really that stupid?

If you are running a 4.8v ignition with a 4.8v battery, where is the logic in using the battery below 4.8v? In any case, the engine will tell you when the battery is too low. Hopefully you have enough time to land safely before the engine stops. If you check your batteries, and I hope you do, it should be able to hold a 1 amp load and maintain 4.8v if it's a 4.8v battery. For flight batteries it better be able to hold a 2 amp load.

Speaking of Eneloops. I put my Yak away around the end of September last year with a fully charged 4.8v Eneloop on the igniton battery. Pulled the plane out yesterday and checked batteries for the first time this year. The Eneloop was at 5.2v. Not shabby at all for a nimh.

That's the nice thing about them.
They are stated to hold 80% of the charge after 12 months (from memory)
They are cheap, simple, easy to use as ignition batteries and deadset reliable

My five year old Triton charger can show the mah put back. Many modern chargers will have the same feature. So invest in one. Why do you want to estimate something that you can precisely measure?

I have a Sirrus Smart charger. It is about 10 years old. Do you think it would be ok to use it on the "Sanyo" "Eneloop" 1900MA pack I have? It has a 3 position switch for charging. 250, 500. and 1000. Do these numbers represent the pac size to be charged or the rate of charge? Got find the directions for it! Capt,n

I wouldn't use that charger on Eneloop batteries. It charges at a constant high rate @ over 1A. Those batteries will not be happy with that high rate of charge. The switch just changes the charge characteristics and not the overall rate.

Sanyo states that these batteries can be fast charged on occasion but overall, they should be charged at the 1/10C rate if you expect them to live a long life. While these batteries exhibit excellent self discharge rates, they are still a rather high impedence, NIMH battery. One common characteristic of these sorts of cells is they don't tolerate high charge rates well.

I rather disagree with that.
Look at this spec sheet: http://www.eneloop.info/fileadmin/ED...data_sheet.pdf

I have been using one of those automatic balance chargers for all of mine in NiMH mode and set the max charge current at 1A or 2A depending on the time I have.
John's charger should do fine on either the 500 or 1000 setting

The Eneloop spec. sheet I have in my files at home (not at my current location to post here) clearly states that they should never be charged at high rates without temperature monitoring. Eneloops should have the charge terminated as soon as a very minimal temperature elevation is detected. I don't have the temperature rise spec. handy to quote here ... sorry but I do know that temp. rise tolerance is far less than for other NiMh cells. Charging Eneloops at 1/10 C is considered safe and they will tolerate a fair amount of overcharge w/o cell damage. Yes, you certainly can charge these batteries at a 1/2C rates or even at greater levels such as 1C, but their lifespan will almost certainly be reduced if you don't keep a very keen eye on their temp. rise. As most people don't monitor temperature rise for RC applications, its just easier to use reduced and safer charge rates.

There is no reference to cell temp. rise during charging on the spec. sheet you published. There is just one small reference that proper charging equipment should be used. I would assume that proper equipment would include temperature monitoring.

John's charger only charges at a 1A rate regardless of what the switch setting is. The switch setting only applies to how the charger treats the battery after the peak detection charge cycle is terminated.

I've grown to like these batteries quite a bit for transmitter and ignition applications. But .... I've also grown to respect their limitations.

Point 4: The ignition is rated as suitable for 4.8V packs and 6V packs. That means a range from 4.4V to 7.2V. LiFe battery packs fal within that. The semiconductor is merely an additional safety device.

Point 2: LiFePO4 for the same capacity is lighter and can be fast charged at up to 10C. This means I can use a smaller, lighter battery and charge it at the field while the dodgy pilots fly. I'd rather this than place my hope and faith in battery packs that IMEhave failed too often.

So even though you don't "see"a reason to use them, I certainly do. And its still within the manufacturers specifications.

I have a temp probe on my charger but never used them. I have a habit of touching all batteries I charge though to se if they get hot and don't recall ever noticing a change when I charge at 1A
I'm not familiar with John's charger at all though. Modern day chargers are so cheap ($25 - $50) that I tend to retire the old ones and get the ones with more features. I also notice that when I charge my batteries with 1A as a max current, the charger spends a lot of the charge time at lower rates.
I agree, if a battery gets hot while charging, it's not a good sign. The Eneloops have a rated 1,500 charge lifespan (obviously at normal rates) so even if there is a slight reduction in life span, they give you a pretty good value