Is this NIMH enough? (Full Version)

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zope_pope -> Is this NIMH enough? (5/17/2005 7:05:39 PM)

Hey guys,
I am using a 2700 mah 6V Expert Electronics battery to power 4 standard servos, 2 high speed high torque digitals, and one high speed micro servo. It will be flying in my DP Ultimate. I have flown this before, but after one flight, my voltwatch type device goes to red when the digitals are under load. This leads me to believe that the battery can't provide the required current for my setup. Should I go with a Nicad instead? I was considering a lipo but they sound like too high of maintenance for me. Please help me get pointed in the right direction. Thanks.
Adam



Rodney -> RE: Is this NIMH enough? (5/17/2005 7:49:03 PM)

First, make sure that the switch and wiring between the battery, switch and receiver is a heavy duty unit. Any impedance in this area will have bad effects on everything else. Try plugging the battery directly into the receiver (i.e. bypass the switch and switch wiring) and see if the problem occurs then. Of course the wiring to the battery itself must be at least 22 gage, preferablly 20 gage, with gold plated connector.



zope_pope -> RE: Is this NIMH enough? (5/17/2005 8:07:48 PM)

Well I have the MPI Heavy Duty switch, so it is a heavy duty, but maybe there is something wrong with it. i will go try your advice tonight



Hangtime -> RE: Is this NIMH enough? (5/18/2005 5:19:18 AM)

Hi Zope!

Last time I checked the 2700 'A' NiMH cell had an internal impedance of about 20 mOhms.. compared to most 'AA' sized nicads at about 10 mOhms this could be the source of the issue.. although you've got plenty of capacity with that 2700 pack, high servo loads can cause a shockingly pronounced voltage drop while the loads are applied.

It's not just a NiMH issue.. high impedance nicads behave the same way. You can get high capacity, LOW impedance NiMH packs, but generally the capacity is a bit less than high impedance cells in the same dimensions. The way most modelers with big birds beat the impedance problem of the 2700's is by running the packs in parallel.. in essence running two packs, two switch harnesses. This cuts the impedance in half (now down to 10 mOhms) and doubles the capacity of the system. An effective move in 25lb 3D airplanes, not such a popular move in lightweight pattern and .60 to 1.20 sized 3D birds due to weight gain.

In your shoes with a small DP Ultimate, I'd switch to a low impedance NiMH pack like a Sanyo 1950 FAUP.. smaller than your 2700 pack, yet VERY low impedance.. about 4.5 mOhms as compared to the 2700's 20 m Ohms. Impedance is like a golf score.. the lower, the better. In your situation you'll have plenty of 'grunt' to handle high drain servo's without the scary voltage drop while the loads are applied, and you'll find you saved a bit of weight also.

Hope this helps!



Geistware -> RE: Is this NIMH enough? (5/18/2005 11:23:40 AM)

I did a test and you can make your own conclusion.
I charged a 2700maH NiMH pack and a 1300maH NiCad pack.
The NiMH pack could supply 1 amp for 1600maH then the voltage went below 5.0 volts (5 cell pack)
The NiCad pack could supply 1 amp for 1000maH then the voltage went below 5.0 volts (5 cell pack)

I would get rid of the NiMH Pack.



3D Joy -> RE: Is this NIMH enough? (5/18/2005 2:12:09 PM)

Well said guys.

A friend of mine flied a 2100 mah Nimh pack (AA size) which had an internal impedance of 25. The plane is a WH Extra 300 at 28% (I think) after 3 flights from a full charge, he made a snap and the receiver went into failsafe! Current needed made the voltage to drop considerably...

He doubled up the packs.

The voltage of my batteries (Nimh 2300mah 2 in parallel through their own HD MPI switch) with ONE coreless digital servo stalled drops down more than 1 volt! That is with 2 batteries!

I ordered 2 4/5FAUP at 1950 Mah at 6V for my plane. Yes they are heavier and of less capacity and more expensive but I will NEVER get 2300 mah from my 2300 batteries anyway.

Hope this helps.



zope_pope -> RE: Is this NIMH enough? (5/18/2005 3:59:42 PM)

Thanks guys,
I was thinking about going with NoBS batteries for their very informative site, and their owner even decided to help me. Last time I will buy an Expert Electronics pack. Thanks for the help guys!
Adam



JoeAirPort -> RE: Is this NIMH enough? (5/18/2005 6:05:34 PM)

Rodney so you 2nd Geistware's comment on not using NiMh?



marked23 -> RE: Is this NIMH enough? (5/18/2005 6:45:04 PM)

I've tried three different brands of the "blinking lights" voltage meter type devices. The Voltwatch brand was, by far, the worst at giving me a good impression of my NiMH battery status. A fullycharged GP3300 pack (from Steve no less) could be brought down to the yellow by just moving the sticks aggressively. I tried a similar volt meter that HeliProz sells under the Mavrikk brand. That one is a lot better for reading the health of my 4-cell nimh. The best of the three was the one CenturyHeli sells. It looks just like the Mavrikk one except it has two micro switches on the back for setting different voltages. The one from Century gives me an accurate representation of my battery state.

I think the Voltwatch is just too jumpy. If the voltage dips a bit, the Voltwatch lights move a lot. It was really disconcerting. I quit using it.
I'm talking about the regular Voltwatch. I haven't tried the new (slightly smaller) Voltwatch.

This is just my experience, your mileage may vary.

-Mark



RCAddiction -> RE: Is this NIMH enough? (5/18/2005 7:04:17 PM)

2 observations:

1. Consider using a decent loaded battery tester. I use this one from I4C which can load your pack to 500ma, 1000ma, or 1500ma. It is $50 but saves the cost of buying Voltwatch devices for every aircraft you fly.

http://www.i4cproducts.com/battery_tester.htm

2. Nobody seems to have mentioned that besides wiring connections and/or the battery pack, that there may be one or more bad servos or linkages which are causing excessive current draw due to binding, etc.

3. Zope....in addition to using a loaded battery tester, you should cycle your battery (discharge then charge it on a cycle charger) to see how much capacity you've used up after 1 flight. It will also tell you how much capacity that pack can provide when it is fully charged. If you have a problem with a high impedence connection, binding servo, etc, you might actually be draining the NiMH battery and the Voltwatch may actually be doing its job by warning you.



zope_pope -> RE: Is this NIMH enough? (5/18/2005 8:23:18 PM)

I know that the airplane used about 400 mah range checking, adjusting the engine, and on the first flight. I used my trusty accucycle to get that number. It could also be a bad servo, but not a bad linkage as I have done the same test by hand (loading the servo arm with my fingers).

I am not actually using a voltwatch. I am using the MPI HD Switch with the voltmeter lights built into it. I am not sure how accurate it is, but since this is my favorite airplane, one can never be too careful.



Geistware -> RE: Is this NIMH enough? (5/18/2005 9:29:36 PM)

I have used the voltwatch and I4C units.
The Voltwatch is accurate with NiCad's
On NiMH, it gives you a false impression because the discharge vure is flat until the pack is almost dead.
I never knew the internal loading of a NiMH pack was so high until I measured it.
Almost half the pack is useless for high load applications.



famousdave -> RE: Is this NIMH enough? (5/18/2005 9:51:10 PM)

1> Voltwatch and Expert power monitors are worthless, they are way too sensitive to transients to be of any benefit whatsoever.. they are a gimmick
2> Use a low impedance pack like Steve Suggested (Expert packs are cheap high impedance packs) and don't be fooled by big capacity numbers
3> Use a H9 Load test meter and apply a 500mA load (single pack) and make sure it stays above 6V (i.e. no-fly voltage is 6V)
4> Fly and don't worry about NiMh, it is a lot better than NiCd.


PS: Li-Ion is far LESS maintenance than either NiMh or NiCd. The only bad thing is you need a special charger which costs about $100 and you have to use regulators which could introduce another point of failure. Other than that there is ZERO maintenance.

NiMh cells discharge themselves over time so they require topping off every so often
NiCd cells need to be cycled regularly or they get memory effect

With Li-Ion you just charge and use, kind of like filling a gas tank - you only need to be religious about read the charge state with the load meter between flights. I have literally gone 4 weeks and flew 20 flights on a single charge. NO BS!


Many times in smaller planes NiMh is the best solution as you need the battery weight to tune CG anyway - why go with a light battery if you have to add weight elsewhere??!
DP



RCAddiction -> RE: Is this NIMH enough? (5/18/2005 11:56:07 PM)

Zope, I'm very familiar with the MPI switch with built-in LED's. It was actually my idea, which I provided to Jarvis (Maxx Products owner) one night when he visited Venture Hobbies. He lives nearby and I see him periodically.

The MPI switch has a wire you clip for 4.8V or 6V. Make sure it's set for the right voltage. I believe you said your pack was 6V, right? Are you running a regulator between the battery and switch which might reduce the voltage and be fooling the battery indicator?

Anyhow, as several have indicated, you want to check any pack with a decent loaded voltmeter to be sure what you have. It is possible that the MPI indicator is defective and that your battery is fine. Cycle the pack to check its total capacity. It should be close to 2700. If you get something like 2000 or so, it's probably a failed pack. Maybe a bad cell.

I am a bit surprised that people don't care for the 2700 Expert Sanyo NiMH pack:
http://www.horizonhobby.com/Shop/ByCategory/Product/Default.aspx?ProdID=EXRB301

I don't know why people are dissing it. I've used the 2700 mah Expert pack (Sanyo A cell) on a 120 sized Giles with all digital servos and it performed very well. Dave Thacker (Radical RC) mentions the Sanyo 2700 NiMH pack on his site "One of my good flying friends uses one of my 2700 packs in a 1/3 scale Aircraft International Extra with 9 JR coreless servos. He has about $4000 in this ship and is one of the most respected pilots in the club. With NiMH, he has a huge capacity reserve and a light weight pack."






zope_pope -> RE: Is this NIMH enough? (5/19/2005 12:20:31 AM)

Well i have cycled the battery and am getting a little bit over 2700mah in the pack. I am not running a voltage regulator, and I have clipped the wire so that it is setup on 6v. I think i will fork out the money and get a battery tester after work today. let me explain the setup of my airplane. It is running 4 standard 3004 servos on the ailerons. the right servos have an extension, plus a y connector that goes into the rx. Same thing on the left. I have a high speed micro servo on the throttle, and a 5945 on the elevators and a 5645 on the rudder. What load should I test my batteries at? Thanks



RCAddiction -> RE: Is this NIMH enough? (5/19/2005 3:20:07 AM)

The best thing to do is to try to measure the current draw your plane experiences when the servos are presenting a load to the battery. If that is not practical, for 5 analog plus 2 digitals, I'd go for 1 amp on my I4C. If you get a standard RC loaded tester you will likely not be able to set the load. Not sure but I recall that some of the basic models are in the 300ma range. Someone who knows for sure, please jump in.

It's a good idea to compare the voltage, under load, to other known good 6V batteries. Also, not a bad idea to unplug the battery from the switch and to connect directly to the battery for testing purposes.




Rodney -> RE: Is this NIMH enough? (5/19/2005 3:42:28 PM)

You that complain about the voltswatch sensitivity may be underselling the unit. The information it is giving you is very pertinent. When it drops down in the yellow etc. when you cycle the sticks rather agressively, it is showing you that you have potential problems in that the voltage drop in the switch and wiring between the battery and receiver is marginal. This is valuable info and not a problem, in fact an advantage.



marked23 -> RE: Is this NIMH enough? (5/19/2005 6:31:47 PM)

Rodney,

I only use NiMH batteries. Maybe the Voltwatch works better with NiCds.

I did my tests with the Voltwatch on my helicopters that are both in a known-good setup. There is not a switch problem, because I tried two different switch types (one was a Gem super rocker, the other JR).

I started with fully charged RX batteries and tested each meter. Both a static test, and an agressive stick movement test. I also do a stress test with the eCCPM heli where I lift the helicopter off the table by its swashplate. I observed each meter's reaction to each of these test and compared it to what I expected to see. Century > Mavrikk > Voltwatch.

Then I discharged the RX batteries by 2000mah. In my safety protocol, this is below my safe-to-fly limit. I did the same three tests on each of the meters. The Voltwatch didn't even register on the red. It just wasn't lit at all. The Century and Mavrikk both showed the battery as being in the red... exactly what I wanted to see for my safety protocol. Again, Century > Mavrikk > Voltwatch.

I don't exclusively rely on the meters. I also use a loaded tester. But the meters are very helpful to see when something has abruptly changed, like something binding.

-Mark





Hangtime -> RE: Is this NIMH enough? (5/19/2005 7:39:07 PM)


quote:

ORIGINAL: RCAddiction

I am a bit surprised that people don't care for the 2700 Expert Sanyo NiMH pack:
http://www.horizonhobby.com/Shop/ByCategory/Product/Default.aspx?ProdID=EXRB301

I don't know why people are dissing it. I've used the 2700 mah Expert pack (Sanyo A cell) on a 120 sized Giles with all digital servos and it performed very well. Dave Thacker (Radical RC) mentions the Sanyo 2700 NiMH pack on his site "One of my good flying friends uses one of my 2700 packs in a 1/3 scale Aircraft International Extra with 9 JR coreless servos. He has about $4000 in this ship and is one of the most respected pilots in the club. With NiMH, he has a huge capacity reserve and a light weight pack."


There's not a thing 'wrong' with the Sanyo 2700 AU's.. It was considered the 'gold standard' for years in big IMAC applications, simply because up untill last year it was the 'only game in town' for high capacity and light weight. Up untill we came on the scene most folks just bought packs based on capacity; and no battery assemblers published impedance specs on their battery packs.

What's changed in the hobby recently has been the type, grunt and quantity of big bird servo's being offered, the loads they pull and the type and style of flying done with these big birds. Frankly, at 20 mOhms impedance, regardless of capacity; the voltage drop of a SINGLE 2700 in front of 5 or six big digital servos flying a 30 pound IMAC ship thru a 'Wall', 'Avalanche' or repetitive snap rolls can tag upwards of 20 amps for 3-6ms knocking the voltage down to under 4 volts while the loads applied... no bull; we've checked the telemetry. Often this kinda current load is enuff to trigger a fail-safe lockout or a mighty fast trip to the dirt. Several years ago, folks started routinely running the high capacity NiMH and Li-Ion packs in parallel to cut the voltage drop and provide a bigger voltage reserve under load. Again; there's nothing 'wrong' with the 2700's.. they just ain't the best pick anymore for this type of flying.

Nowadays, NiMH cells have become available to us in the hobby that have significantly lower impedance. (ex Sanyo's 1950FAUP at 4.5 mOhms) Further, folks like me started barking about the importance of checking impedance AND capacity against the type of flying and radio gear BEFORE making a choice on which cell type and size to use; we were the first to publish impedance data on our spec sheets & the website to help folks compare impedance vs capacity and make better decisions. Better cells for the applications we fly and better assembly techniques coupled with good setup and load support gear like HD switches & powerboxes make the difference between a 'marginal' setup and one that can shoulder loads without tripping the low voltage hooter.

Hope this helps!!



Hangtime -> RE: Is this NIMH enough? (5/19/2005 7:40:52 PM)

whups.. system hang; double post. Sorry!



zope_pope -> RE: Is this NIMH enough? (5/20/2005 12:19:17 AM)

Hey Steve,
Thanks for getting the battery pack I ordered out so quick. I cant wait to test it out. I am going to test out my setup on a known good Nicad tonight to see if indeed it was my 2700mah NiMH. Thanks again.
Adam



JoeAirPort -> RE: Is this NIMH enough? (5/20/2005 12:50:13 AM)

I ordered the Sanyo 1950FAUP at 4.5 mOhm. Thanks for getting mine out too.

quote:

ORIGINAL: zope_pope

Hey Steve,
Thanks for getting the battery pack I ordered out so quick. I cant wait to test it out. I am going to test out my setup on a known good Nicad tonight to see if indeed it was my 2700mah NiMH. Thanks again.
Adam




rajul -> RE: Is this NIMH enough? (5/20/2005 12:54:58 AM)

I received this statement from a charger manufacturer:

"It is recommended charging NiCd/NiH with higher current then C/10 if
you use the battery with higher discharging pulses. rx batteries
charged by C/10 failed at the voltage when higher discharging pulses
are needed. If the voltage is too low for a short moment, the rx fail-
safe takes over flying your model.
If you need high discharging current then you have to charge with higher current. e.g. the
other extreme is using NiCd/NiH batteries in electric flying models you
have no power in using a C/10 charged battery, but you can operate at
full capacity with a >2C charged battery"

FWIW...............



zope_pope -> RE: Is this NIMH enough? (5/20/2005 1:19:14 AM)

haha, me and joe are doing the exact same thing. I charge my nimh batt at almost 1c so I am not sure if the problem was in the charging, but who knows. From what i read though no bs batteries look the way to go if you aren't going lithium. [:D]



rajul -> RE: Is this NIMH enough? (5/20/2005 1:35:17 AM)

I just bought a 2300mah Nimh for my radio, and the supplier site says that it should not be charged above C/2. There was no explanation given.



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