Yale

My Feedback: (1)

Connecting 4.8 and 6v.batt.to each sw. then to receiver,in the on time what is going on with 2 different volts?any harm being done?I have a couple of planes with this set up ,so far no problem,,just not sure

mr_matt

My Feedback: (10)

the higher voltage battery is basically "charging" the lower voltage battery.

THat is there is net positve flow of charge into the lower voltage pack (the 4.8 volt)

So basically your higher voltage pack (6V) has been powering your airborne system and trickle charging your 4.8V

Geistware

My Feedback: (16)

NEVER mix voltages on a battery installation. Either use 6 volts or 4.8 volts not both! Basically what happens is that you will use a lot of your 6 volt capacity trying to charge the 4.8 volt. If you take the 6 volt pack down to 4.8 volts, it could damage the 6 volt pack.

Red is the man to ask about such things.

pepito9

you say you have a couple of planes with that setup, why don you have one on 4.8 and two packs and another one on 6.0 and two packs?

that way they are all happy and matched without all the concerns you are having now.....

diego

Volfy

My Feedback: (23)

Essentially, the only power source will be your 6V pack. Your receiver, servos and the 4.8V pack will all be loads on that power source, each drawing some current. So, there is really no danger in doing this as long as you don't drain the 6V pack past its capacity. But then again, your 4.8V pack are serving two functions: as a deadweight and as a drain on your power supply, both are burdens on your plane and flight system and yield absolutely no benefit.

The conclusion is pretty simple: don't do it!

mglavin

My Feedback: (31)

I'd like to add to the melee and suggest that it really is insignificant when you consider entire scenario. Obviously you've proven that it works... I would not recommend doing so, but whatever....

1] A 6v battery has insufficient power available to charge a 4.8v battery. Fact not conjecture.

2] There are some basic considerations that should be considered.

A] The power demand will source the path of less resistance.

B] More cells is more resistance, higher static voltage discharges at a accordingly at a higher consumption rate. But there are other considerations...

C] The sum total of the battery or batteries in the case will only be as good or powerful as the individual cell with the least desirable specifications.

For the sake of discussion can you cycle the batteries, fly the model and cycle the batteries in your model and report the finding's??? I think many will be surprised...

golf_lake

A question for Michael Glavin Would you consider continuing to charge your fully charged 4.8V battery @ 6V with no means of regulating the charge rate, because this is what is happening.

Further you say “1] A 6v battery has insufficient power available to charge a 4.8v battery. Fact not conjecture.”
What is the Amp hour rating of the 6V pack? because this is the power available to over charge your 4.8V pack.

Benefits of mixing your voltage = zero
Minuses = overcharging your 4.8V pack, reducing it life, wasting the energy from your 6V pack by turning it to heat by overcharging the 4.8V battery, risk of damaging your 6V pack by having a load from the 4.8V pack with no means of regulating current, if this is excessive, a risk of burnt wires or a fire at worst.


Michael Glavin you say “C] The sum total of the battery or batteries in the case will only be as good or powerful as the individual cell with the least desirable specifications. “ true in a series configuration but not so in parallel and this is what is being done.

Yale Please save yourself a lot of grief and do not put different voltage packs together.

mglavin

My Feedback: (31)

The reality of the 6V battery charging the 4.8v battery in theory has some credence, however in this application the source or charge voltage is to close to the latter's voltage. Additionally I assume the switches are only on while the model is being flown, not sitting around soaking up stray power. If the 4.8v battery has been substantially depleted say to 4.0v and the 6.0v battery was fully charged they may be some transference of power I'd guess in the neighborhood of 20% or less in this circumstance.

Assuming again the switches are on simultaneously and in flight the current draw of the flight system will load both batteries. Both batteries are discharging power. The 6v batteries mah capacity is not responsible for charging it's the higher voltage. If the 6.0v battery voltage is maintained higher than the 4.8v pack voltage, the 6.0v pack will provide some charge potential, length based on mah capacity and voltage. Again you'd realize this over the course of time not a flight ot three. The discharge voltage of the 6.0v pack must be higher or the 4.8v battery will not see the voltage required to charge itself.

I think realizing overcharge of the 4.8v battery with the 6.0v battery during the course of several flights is an extreme exaggeration and unlikely. Over the course of time with all things stacked in favor and given sufficient time I suppose it is possible.

Series-parallel operation is occurring. Were stacking cells in series to obtain 4.8v or 6.0v. We then parallel the battery packs and consume power. If one or more cells drops off the discharge curve it will effect the other cells ability to provide the desired voltage and capacity. Why would parallel operation effect this?

I agree there is no advantage to mixing dissimilar battery voltages. Using batteries of different capacity and like voltage are acceptable. Again I am not suggesting anyone do this battery voltage mix thing, however I have seen many do so over the years with no ill effects that I am aware of.

Volfy

My Feedback: (23)

Mike, I think you should check the output voltage of your TX/RX wall overnight charger. More than likely it's around 6V on the RX output. 6V is 6V, whether it's from a battery pack or wall charger. Current will flow from the 6V pack into the 4.8V pack. I will hook up an ammeter when I get home tonight and report back here just how much current.

If you meant to say that a 6v battery has insufficient power available to fully charge an already discharged 4.8v battery of similar mAh rating, then yes, I agree.

Certainly no one here so far is encouraging the use of 6V packs. That decision should be left to the individual to decide whether the benefits outweigh the disadvantages. We are only discouraging mixing of different voltage battery packs.

Gordon Mc

My Feedback: (11)

One point that you may be neglecting here, is that we don't have 4.8v packs and 6.0v packs - we have 4 cell packs and 5 cell packs. A fully charged 5 cell pack is *way* over 6v. Last time I checked the unregulated voltage on a freshly charged 5 cell pack, it read 7.4v.

Regs,
Gordon

Volfy

My Feedback: (23)

Mike, I don't think it's a good idea to view this scenario as a kind of serial-parrallel operation. What we have are connections of two battery packs and several loads (RX and servos), all in parallel. The question is whether current would be flowing into or out of the 4.8V pack. If it is flowing INTO the 4.8V, which it has to be if there is a 6V current source present, then no load is drawn from the 4.8V pack.

Just because something has been practiced for years with no seemingly ill effect doesn't automatically mean it's a proven operation. I still see many drivers idle their cars in the parking lot and driveways to "warm up" the engine as if there some benefit to the engine. Now I doubt it will do the engine immediate harm, but if all you're doing is wasting gas, polluting the air and running and engine at idle and low oil pressure, with no benefits to your engine, then why do it?

thomasb

OK, I tried it. From what I measured, a 5-cell pack, connected to a 4-cell pack, WILL drive significant charge current into it. Even when the 4-cell pack is already charged.

I tried a couple combinations. I get well over 600mA being needlessly dumped into the 4-cell pack. That is a substantial charge current and may stress a typical 600mAH pack that is already fully charged. Besides that, it is a drain on the 5-cell pack that serves no purpose.

My opinion: In dual pack R/C applications, you can mix capacities, but not voltages. Red's R/C clinic web site has more info on how to do this safely.

Volfy

My Feedback: (23)

Hey Thomas, you beat me to it!

I can think of one benefit here: IN-FLIGHT BATTERY CHARGING!

thediode-RCU

Thomasb has it right!
If each battery is connected to a different switch and only one switch closed in any one instant, the user simply decides whether he wants to fly on 4.8 volts or 6 volts (nominal voltage, assuming a full load voltage of 1.2 volts per cell).
If, however, he closes both switches, the difference of 1.2 volts between the two batteries will be spent overcharging the 4.8 volt pack, and lowering the voltage of the 6 volt pack below the safe voltage, (usually assumed to be between 1.05 and 1.1 volts per cell), thus subjecting the 6 volt pack to an abrubt voltage drop while under load.
Most radio mfgr.s warn against using your batteries at below 1.1 volts per cell, because of the discharge curve of nicads seeming to break into a much steeper discharge curve below that voltage.
Why flirt with disaster. Simply choose which one you like, and use it, but never use both at once.

mglavin

My Feedback: (31)

I don't want to beat a dead horse but the scenario in question is somewhat different than just coupling two batteries of dissimilar voltages and observing the mA creep for a moment or two...

In general I agree that a higher voltage source will charge the lower voltage battery. That said the are other variables at play here.

Electrons source the path of least resistance. A 6V pack has more resistance than a 4.8V pack.

Power consumed at a higher voltage will discharge at a higher rate.

Power/current is being consumed simultaneously to the purported charge phenomena.

Simply measuring how much current can pass without a load is not accurately depicting the discharge of the two batteries while in use in a model. Additionally the 6V battery will not discharge a flat line curve to the 4.8V battery for a sustained time. The rate at which it may charge the 4.8V battery will drop sharply as time goes on. The source and the recipient voltages are to close together.

I'd like to do a test just to satisfy my curiosity. Not being a techie by trade I learn things as I go. How would you guys suggest we simulate and record the actual current draw from each battery while observing the voltage and power either coming or going?

Thomas how did you measure the mA creep. I assume you coupled the common of both batteries and attached a DMM in series with the positive leads of the batteries, utilizing a mA scale. Without benefit of a load?

I am thinking of cycling a 6V and 4.8V battery, recording the results, then parallel couple the batteries, discharge them for 30 minutes at 1A/1000mAh and then cycle them and see which used more power. This may shed some light on the actual use and depletion of the batteries.

golf_lake

Michael Glavin my intention is not to offend you but this needs to be said. You have a large number of posts under your profile and signing your posts as a Moderator. You are giving long explanations that could sound credible to anyone that does not know better.

As a member/moderator that has made that many post you have a duty of care to new members or the less knowledgable, they would assume you to have a lot of knowledge/experience on this hobby and you very well may have generally.

Please go and talk to an electrical engineer, technician or a licensed Ham operator before giving any further advice to unsuspecting people about electronics and electrical theory.

If I misunderstood what Yale was asking. 2 switches and using them one at a time, this would be of no benefit and just add weight for no good reason.

AGAIN DON’T MIX PACKS of different voltages at the same time.

Rodney

It is with some regret that I am sending this; but, the information being given out by MGLAVIN is so bad that I must warn against anyone taking it as good advice. I hope he will contact an electronic engineer or even a physisit so that he can get some correct info. If you are in doubt, do some of the test mentioned above yourself. His advice will almost certainly cause you to ruin one or more of your batteries.

mglavin

My Feedback: (31)

Geez guy's. Did'nt you note that I did not suggest that anyone use batteries of dissimilar voltage, I think I mentioned it more than once.

I pointed out that the are other factor's at play and that I know of several pilot's that have used 4 and 5 cell packs without problems...

I also suggested test's may indicate information that some would be surprised of.

As far as counsel with Electronic's professionals, I do this frequently. I often do not understand the in and outs of specific technology. I ask questions, do research, perform tests, compile data first hand and that offered by other's.

If I make a mistake someone almost always brings it to my attention. This is a Discussion Forum.

Theory and purists do not provide all the answer's. The are many factors and scenarios that propagate cause and effect. I find interest in looking into things that many suggest is of no value, the answers are known, So what... I don't believe everything that's tabled... I find many times that information is inaccurate and incorrectly applied to the question or use at hand...

Volfy

My Feedback: (23)

Mike, I'm afraid I agree with golf_lake. If you aren't sure, then it's best not to risk misleading the uninitiated.

You've mentioned several factors that, frankly, don't have much to do with the topic at hand. For example, the fact the electrons seek the path of least resistance is certainly a fact, but the question here is one of electrical potential, first and foremost. Current will flow from points of higher potential to points of lower potential.

If two battery packs of different voltages (i.e. electrical potential) are connected in parallel. The difference in electrical potential WILL cause current to flow form the higher to the low. It's that simple.

If you hook up your RX and servos, also in parallel, these will present NO electrical potential with respect to the two packs, and currently will flow into those devices from the higher voltage pack. Since current is already flowing INTO the lower voltage pack, no current can flow OUT OF it at the same time.

If you want to experiement, just hook up everything as described and plumb in a ammeter inline with the 4.8V pack. If current flow into it, then you'll know what we say is correct.

mglavin

My Feedback: (31)

I understand electrical potential as such:

A unit of electric charge expended in moving a charged body from a reference point to any given point in an electric field.

It can be shown that the potential associated with a charged body at a given point in a static electric field is independent of the path along which the body is traveling and passing from infinity to the given point. Potential is measured in volts and is commonly referred to as voltage.

A battery has a potential in relation to emf, which causes current to flow in an external circuit. The difference in potential - potential difference (pd) - is expressed in volts.

OHM's Law suggest's the rate of flow of the current is equal to emf [electromotive force] divided by resistance.

Do I understand this correctly? Doe this apply to the scenario at hand?

I did some preliminary test's.

Peaked charged a 4 and 5 cell JR Extra NiCad battery packs on Sirius Equipment. Voltage off charge was 5.75 and 7.01 respectively.

Using two precession Fluke DMM's as mA measuring devices, three other DMM's and a Sirius Super Tester I connected all to display pack voltage, mA movement, average discharge voltage and the total mAh's consumed. I verified the mA movement charge verses discharge.

With a 500mA load, which I think conservatively represents the load you'll see in a model with dual batteries and multiple servos.

4-cell pack discharged at 110mA to 4.94V at termination.
5-cell pack discharged at 373mA to 6.37V at termination.
Average combined discharge voltage 6.01V.
The total measured discharge consumption was 650 mAh over
approximately one hour and fifteen minutes...

The 4-cell pack temperature averaged 77 degrees.
The 5-cell pack temperature averaged 76 degrees.

Coupling the battery packs together without a load showed a 225mA charge to the 4-cell battery over the course of a few minutes. If you let this continue the rate of charge diminishes as the "pd" closes the gap.

I'm discharging the batteries presently to see what was discharged by each battery pack respectively.

I am going to do the test again at a lower discharge current to see what it reveals.

Four_Stroker

My Feedback: (10)

I think you will find if the 6 volt pack is fully charged and the 4.8 volt pack is discharged a large current will flow to the 4.8 volt pack. As the 4.8 volt pack is charged the charging current will go down.

Don't parallel different volatage packs!

mglavin

My Feedback: (31)

I did some additional testing as described in my previous post. Same batteries and test equipment setup. Several tests confirmed the previous findings as well as those below.

250mAh load on the batteries revealed:

5-cell, 327mA draw at start of cycle and diminished to 278mA @ 6.24V.

4-cell, +174mA positive charge at start of cycle and diminished +15mA @ 5.31V.

This 250mAh load is IMO not representative of the consumption in a model. 250mA equates to .25A load, 250mAh factors to a load of 4.166666mA per minute.

The 500mAh load in the previous posts equates to 8.333333mA load per minute. Again this minimal IMO and not representative of a model using dual battery packs.

A typical 8 servo model will consume 30mA a minute or 1800mAh or 1800mA per hour.

The 4-cell battery does receive a charge that falls off considerably as time marches on . The 4-cell battery did not get any hotter than the 5-cell battery as measured with a laser temp gun.

The load on the batteries and the resistance of the batteries is a factor, these variables account for the splayed results as related to theory.

In any event I do not suggest anyone use batteries packs of mixed voltages. Mix capacities all you want. Keep in mind mixed capacities will discharge the load in ratio to the battery packs mAh difference's.