The Benefits of Using hitec battery

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ORIGINAL: Rafael23cc
There is a big difference between noticing the power difference in an electric-powered aircraft based on the battery's capabilities and detecting a 0.02 sec difference in servos with a 1.5-volt difference. If you can do that, you belong with Andrew Jesky and the XFC elite. For amateur flyers like us, these subtleties are negligible.

http://www.hitecrcd.com/products/dig...l/not-set.html

You also see a torque rating change from 333 to 403 oz*in between 6v and 7.4v, which is 17% of the total rating. Even an amateur can feel this in practice. For instance, take a 50cc to 85cc plane with a single servo per aileron. Climb to altitude, roll it, and if the roll rate decreases (which should increase if the servos are functioning properly), it might result from insufficient servo power. A marginal or underpowered servo would show this difference, potentially due to pack voltage if indeed that 70 oz*in matters.

1.5V is a significant portion of the servo's overall voltage (1.5/7.4 = 20%). It's akin to the 4.8 to 6V variation, which I feel makes a noticeable difference. Initially, I hadn't seen the 7954SH specs, so my question seemed moot once I realized they weren't using an internal regulator. While most fly their packs at the higher end of the lipo discharge curve, knowing the curve's slope isn't optimal isn't satisfying. If I'm investing in high-quality servos, I'll spend more for a better battery choice, sacrificing some power for consistent performance.

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ORIGINAL: Rafael23cc
I love your signature line. I'm an Engineer and an RC helicopter pilot, where control, speed, and precision differentiate a successful flight from a crash.

With the proper attitude, the worst thing that happens is we learn something new.

Joe

I agree that I can't distinguish a delta time of 0.02sec/60 deg in an unloaded sweep. Yet, consider the torque rating change from 333 to 403 oz*in between 6v and 7.4v. This is 17% of the total rating and will be felt in practice. You don't need AJ's expertise to take a plane high, do some blenders, and feel the snap. Another test for sufficient servo power: climb to altitude and roll down; the roll rate should speed up if the servos function well. An underpowered servo would show this difference, potentially attributable to pack voltage if that 70 oz*in matters. 1.5V is 20% of the overall servo voltage (1.5/7.4). It's comparable to the 4.8 to 6V swing, where I can feel the difference. I hadn't seen the 7954SH spec initially, so the question seems moot now. I realize they aren't using an internal regulator. Again, knowing the upper end of the lipo discharge curve isn't enough for me. If I'm investing in high-quality servos, I'll opt for a better battery for consistent performance. We love to argue when we think we're right, don't we? With the right attitude, the worst thing that happens is learning something new. Joe

As usual, one of these askJOHN articles results from a question. This one arose from a forum post where I responded, but was criticized for giving a lengthy answer. So, I copy-pasted the info here for those interested, where it should have been all along.

My response was to a multi-paragraph query from which I’ve extracted bits;

Q1. Is there a downside to overspecifying the power? Plus a related comment...(I have) a Power Expander thingummy with a mag switch... (and) 2 x AR LiFe batteries...

A1. Addressing this involves delving into battery chemistry, affecting voltage and servo output, related to the servo's specs. Plus, it touches on the thingummy and LiFe batteries, explaining why my response is lengthy. Simple questions rarely have simple answers because they're often complex. I'll explain (of course).

Context is Everything

When addressing battery chemistry's effect on servo performance (determining if you're overspecifying the servo), and since I'm often asked my favorite chemistry, this article addresses multiple points. We'll touch on the thingummy, which was mentioned but not questioned.

To address servo torque needs, we must discuss voltage's effect on servos, leading to battery chemistry! The mention of 2 batteries and a mag switch adds another layer. See how quickly questions get complex?

Thus, I'll explain why I think it's wise to:

1. Overspec the servo for the task,
2. When to underspec, and
3. Why I prefer certain batteries (depending on the model).

To summarize (TL;DR):

1. If you can afford it, overspec, so servos work below their ultimate need.
2. Overspec or underspec depends on you and the model.
3. I prefer A123 technology for ease of use.

Nothing beats a servo that works below its capacity most of the time. It faces less stress and handles extraordinary demands easily. An overspec servo can manage unexpected situations, like an overweight model in a terminal dive. But the pilot and model affect servo selection too—and explaining why I prefer LiFePO4 batteries is complex; trust me if you don't want to read on.

Follow-up Question

Q2. Is there a downside to overspecifying a servo? Assuming the surface to be moved is the same, does a servo rated 4X the need use more current than one rated 2X? Assuming other parameters are equal.

While thinking, I doubt an elevator needs more force than the model's weight to deflect it. Am I wrong?

Let's quickly resolve this in reverse order:

• Yes, you're mistaken—more details later.
• 4X vs 2X: Current draw is almost the same regardless of the servo. Why? Because if you need 150oz-in, our DS180DLHV or DS1155BLHV will draw nearly the same current for 150oz-in of force. As will other brands, like the Hitec HS-D645MW.

So, if you can afford it, should you use a DS1155 for a task requiring a DS180? Yes!

However, in reality, budget constraints mean you won't use a DS1155 on a trainer (we'd recommend a $30 DS90). Yet, we have a customer using four $160 servos on a SIG Kadet trainer. Why?

Because he has the funds and wants the best servos regardless of cost, including one on the throttle. But I digress.

Long Answers

Overspecifying depends on voltage, which I'll explain. Using our popular DS180DLHV servo (similar to Hitec's HS-D645MW with similar performance) as an example:

Why mention these servos? Two reasons: many modelers are familiar with their performance, and they share similar size, price, and performance.

Our DS180DLHV is popular with modelers, likely because 180oz-in @ 0.17sec/60° hits the sweet spot. Plus, for $40, you get all-steel gears, 13 o-rings, a finned alloy center case, bronze reinforcement at the gear shafts, and it meets 3 MIL-STDS; great value for money.

Next, analyze the DS180DLHV's specs. Note three things:

1. We provide specs for 5 voltages instead of just two.
2. Higher voltage means better performance (true for all servos).
3. Manufacturers quote performance at the highest voltage for better marketing.

Now, we need to discuss chemistry, packaging, hazards, and risks before explaining why I prefer certain battery chemistries and overspecifying servos.

Noting five specified voltage ranges, these list various performance parameters across the spec chart.

Battery Chemistry

Why five voltages? Two nickel chemistries are common with two cell configurations (4-cell and 5-cell), and four lithium chemistries (all in 2-cell). This makes six chemistries but divided into 5 columns because two are nearly identical.

Specifically: NiCd and NiMh, plus LiFe, LiFePO4, LiIon, and LiPo.

• NiCd - 1.2V/cell
• NiMH - 1.2V/cell

Nickel chemistries peak at the same potential (voltage). They have 4-cell (4.8V) and 5-cell (6V) pack configurations. So the first two columns are for 5V and 6.0V.

While I state 5V instead of 4.8V, 5V is common in electronics (e.g., PCs provide 5V and 12V to the motherboard). For modelers, 4.8V or 5V makes little difference.

Note; a 6S pack is 7.2V and a 7S pack is 8.4V, but they are too heavy for aeromodeling. They're mentioned for completeness.

We'll ignore nickel-based chemistries going forward. They are considered obsolete due to their weight compared to lithium packs (which have higher capacity). Nickel chemistries are on their way out, but we list specs for them because some customers still favor them.

The Lithium Revolution

The 3rd, 4th, and 5th columns correspond to four lithium chemistries, which have varying potentials (voltage) and risks. The first two are combined into column 3, and the last two into column 4. But this makes 4 columns instead of 5!

Reality for packs in columns 4 and 5 is different from nominal and synthetic voltage sources. Have faith, I'll explain (and it'll make sense)!

Higher lithium voltage increases fire risk. So, in ascending voltage order, we have:

• LiFe - 6.4V
• LiFePO4 - 6.6V
• LiIon - 7.2V
• LiPo - 7.4V

These are nominal voltages. I recharge when they reach nominal voltage (except for LiPo, which I push a bit for longer flights).

Point being, a fully charged LiFePO4 (3.3V/cell nominally) stands at 6.9V, while LiPo (3.7V/cell nominally) tops out near 8.4V. And 8.4V is where synthetic sources come into play. I don't favor synthetic sources.

No, the servos don't care, but speed controls fail and usually take the BEC circuit with them, causing a crash. Plus, backfeeding through the receiver-throttle lead can overload the 3.5A plug, inadequate for models with four or more servos. Learn more from these articles:

Battery Packs

The questioner mentioned LiFe packs, which we find unreliable from three vendors, so we don’t sell them. We won’t put our name on risky products. We focus on LiFePO4 packs, which are reliable and used exclusively in our models, except for high-performance 3D and sport models where we use LiIon (not LiPo). And *that's* the TL;DR of my preferred batteries. Read on for the details.

Packaging and Hazards

Why not LiPo instead of LiIon, given their higher voltage? LiPo packaging (polymer bags, like LiFe) is flimsy and meant for enclosed cases (e.g., laptops, phones). Meanwhile, LiIon and LiFePO4 packs come in robust metal shells (like NiCd and NiMH cells). Metal shell packs weigh slightly more but offer greater safety.

Why is this important? A soft-sided pack like LiPo or LiFe may get damaged during violent maneuvers (e.g., crankshaft, snap roll). Even smoothing out a ding doesn’t fix internal damage, increasing failure risk. Worse, failure could mean fire.

Fire Risk

Yes, the potential for fire is a risk I won't take for a slight voltage difference (hence minimal performance gain) or weight difference. I'm not a world-class pilot; the performance difference is negligible to me.

Consider hazardous materials like balsa wood and fiberglass in relation to your workshop/home’s proximity. Hence, I avoid LiPo packs in my models, except for propulsion, which offers performance benefits and can be removed from the model for charging.

Note: LiPo and LiIon packs are always removed, charged under supervision, placed on a fireproof surface, and stored in flameproof bags. The fire risk isn't zero despite these precautions.

The Packs John Prefers Using

As mentioned, LiIon packs go into 3D and sport models but always removed for charging. Only LiFePO4 packs remain in the model and charge in situ, enhancing safety. The upsides of LiFePO4 include safety, despite being costlier and weighing a bit more. Even though I might not feel the performance difference, I prioritize safety.

Note: We spec, not make, our packs. We handle LiIon and LiFePO4 packs with four leads. Two DuPont, an XT30, and a balance lead, supporting two switches for safety.

Leads and Benefits

Yes, four leads! DuPont (Universal) connectors are rated for 3.5A continuous; more current generates heat, harming electronics.

Review the servo specs chart for worst-case current (stalled) and imagine multiple servos working. The advantage of using two leads is evident: they distribute the current load.

The JST-XH balance lead ensures lithium pack cells remain balanced. The XT30 lead on 16AWG wire manages higher current flow. This allows load splitting among receivers, known as load balancing for models with many servos.

For more efb start stop battery information, please contact us. We will provide professional answers. Further reading: 4 Advice to Choose a Scalable Three Phase String Inverter.

Another benefit is redundancy. If a receiver fails, having two maintains partial control, thus landing the model is possible. Even partial control meets the definition of "control" for RC aircraft, right?

Load Balancing vs Thingummy Systems

Thingummy and 'box' systems could connect two receivers for full redundancy and gyro integration. However, they add complexity and potential failure points. Each additional component increases the likelihood of system failure, contrary to intuitive modelers' beliefs.

Component Count Matters!

Thingummy systems involve numerous components, which statistically increase failure risk. Though manufacturers promote safety, the reality is more components mean higher failure chances. We, ProModeler, choose not to sell such systems to avoid unnecessary risks and focus on reliable solutions.

Simplicity is key (KISS - Keep It Simple Silly). Using two receivers in parallel splits the load and maintains partial control of the model in case one fails.

The PEXD Adapter

The PEXD adapter allows extracting 14A via four DuPont connectors. Silicone-insulated wires ensure flexibility and abrasion resistance. Our packs range from 650mAh to 6000mAh, addressing different needs.

Dual-Lead Battery Pack Advantages

One advantage of dual leads: allowing the receiver to draw 7A without heat buildup. Note: any single-lead battery pack is a 3.5A device. But a pack with two leads delivers 7A (3.5A