Electronics and Batteries
– original article by Frankie Novak, updated by Mike Wyatt 5/16
De-mystifying the subject of electronics and batteries, including battery charging and chargers.
Technology: battery and charger technology is moving at a very rapid pace. This pace is primarily because
of RC car racing and model airplanes, where the plane or car runs for, maybe 4 minutes, and in that time it
uses massive battery power; then the user needs to recharge those batteries in minutes to be ready for the
next race. This is NOT the application in RC sailing. We do not need nearly so much sophistication and the
cost that comes with that technology. So, don’t try to apply what the hobby shop guy (selling all this
technology) tells you that you “need”!!!
I. Transmitters ("radios" or TX)- a brief summary:
A. You don't need a sophisticated radio. A 2.4 gHz 4, or 5-channel aircraft (sticks instead of wheels)
will be fine.
1. As you buy "better" radios, you get the ability to program in varied response and
sensitivity, plus the better radios will work with multiple models- incl. boats, planes, and
copters.
B. Buy the brand that most in the club sail. That way, if there is a failure, somebody will be able to
help figure out what's wrong, and even loan you a backup radio. I would avoid brands sold
and shipped from Asia. True, almost ALL are made in China, Tiawan, or Indonesia, BUT a
radio you have to buy from there, while cheaper, also is basically a throw-away. A brand
sold in the USA and serviced in the USA can be repaired in the USA.
C. As you get "more serious" in the hobby, consider buying a lesser version of your regular radio as
a backup. OR- if you started with an inexpensive radio, as you "get serious"- buy a better
compatible one within the same brand.
D. Take care of your radio. Consider transporting it in a plastic gun case (avail at Walmart or any
sporting goods store). That way it is less likely to get knocked around in the car. You can
even buy pre-cut foam liners for these cases, cut for specific models of radios.
E. Brands: the low-price leaders are Tactic, and Spektrum; higher-priced are Futaba, JR, and
European brands like Graupner. Here's a look at four choices among Spektrum, the leader
in sales to RC sailors:
DX5-e (discontinued)
New (11/15) DXe
List: $ 89.99/ w receiver
List: $ 89.99/ w receiver
Street price: $ 59.99 no receiver $ 59.99 no receiver
#models 1
#models 1
Channels- 5
Channels- 5
voltage ind.- LEDs + beeping
Progressive beeping
servo reversing via slide switch
servo reversing via slide switch
No adjustable sensitivity
Adjustable sensitivity via computer interface OR Android phone (requires
opt. cable)
Can download settings off the website (but these are presumably for planes and/ or copters, not boats)
More advanced radio options:
DX6-i
New DX-6
List: $ 129.99/ no receiver
List: $ 229.99/ w/receiver
$ 129.99 no receiver
$ 199.99 no receiver
#models 10
# models 250!!
Rate settings -2
Rate settings -3
Channels- 6
Channels-6
-servo reversing
- servo reversing via slide switch
-adjustable sensitivity
- adjustable sensitivity
-end point adjustment
- end point adjustment
--- all via roller and onboard screen --- all via onboard voice and screen
Voltmeter- screen
Voltmeter- screen
Countdown timer
Countdown timer (talks) in multiple languages.
II. Batteries– Separate battery power is required for the transmitter and to operate the radio receiver ("RX")
and two control servos. Chargers- These are used to recharge the rechargeable batteries used in remote
control sailboats.
III. Battery Capacity and Charging: We use DC batteries, direct current that is different than house current.
Battery capacity is measured in milliamp hours, or Mah. 1000 milliamps = 1.0 Amps. A 1000 mAh
battery can supply 1000 milliamps for 1 hour, or 500 milliamps for 2 hours, etc.
Standard RC sailboats use one battery for the boat (receiver and servos) and separate batteries to power
in the transmitter. The boat electronics (the receiver and analog servos) draw approximately 250 to 300
milliamps per hour of operating, and run on 4.8 to 7.2 volts. (Digital servos draw more– about 400
Mah, still at 4.8—7.2V). So, a 5-cell, 6.0 volt, 1500 mAh battery pack should run your boat reliably for 4
to 5 hours IF fully charged, and using clean, efficient connections, etc.
More voltage 4.8, 6.9, or 7.2 v= more power and better range (radio control at farther away); more
capacity 2000, 1600, vs 1200, 800 or 750 mAh= longer run times.
IV. Batteries:
A. A standard AA-sized battery non-rechargable (like a Duracell), has a 1500 Mah to 2400 Mah capacity
and puts out 1.5 volts. In multiple-cell packs, you chain the voltages together to reach the total voltage,
but the Mah capacities of the cells remain the same. So, 4 X 1.5 V, 2400 Mah cells yield 6 volts, but still
2400 Mah.
There are many different sizes of batteries available, and some can be used to reduce weight. More on
this later.
A rechargable cell puts out less voltage than a dry cell. And– there are other sizes of cells– like 2/3A
cells—that give the same voltage, and capacity, but at lower weight than an AA-sized cell.
Type
Voltage/ cell
Total capacity
4-cell pack
5-cell pack
AA– Dry Cell Battery
1.5
Duracell: 1500 Mah
6.0V/ 1500 Mah
7.5V 1500 Mah
Too Much voltage!
AA– Rechargable
1.2
Varies– 700 to 2300 Mah
4.8V/ ____Mah
Varies by cell
capacity
6.0V ____Mah
Varies by cell
capacity
B. Battery Voltage: RC sailboats use a remote control receiver and control servos at a design voltage
of between 4.8, to 6, to 8 volts (for "high voltage" servos in response to 7.2 volt LiPO batteries). More
on these later. Most electronics are designed for operation in a RANGE of 4.8 v to 7.8 v. On the other
hand, some designed their transmitters to operate on 9.6 volts, (8 AA-sized rechargables at 8 X 1.2 v =
9.6 volts), to a low of 6.0 volts ( 4 X 1.5v AA Batteries).
V. Battery Types – The choice of the right type of batteries for the application will make your RC sailing
experience as trouble free as possible. The following is an overview of the different types.
A. Alkaline 1.5 Volt AA Dry Cells are the most common available batteries. These have a capacity of
up to 2400 mAh, which means the cell can supply a typical 240 milliamps draw for 10 Hours- 2 - 4
sailing days. They are available everywhere.
The big downside of alkaline cells is as the boat receiver batteries, that they gradually yield declining
voltage over their service life. So, less power from your servos, AND a decreasing radio range. But, we
know of sailors who successfully use AA dry cells for as much as half the season.
AA dry-cell advantage: low cost, and simplicity especially if you are just getting started in RC sailing–
using dry cells saves the cost of a charging system. But you’ll buy and throw away a lot of batteries.
B. Rechargable Nickel Cadmium NiCad (NiCD)- These older technology batteries are still available.
and are still used in some devices, but not RC boats. Not Recommended
C. Rechargable Nickel Metal Hydride (NiMH) - have much more capacity (each charge will last longer)
than NiCad cells. They WILL lose charge slowly after sitting in the boat or transmitter, but not so much
as to make the device unisable of significantly reduce usage life (unless they sit for MONTHS).
One downside- NiMH battery packs can fail after just 75-100 recharges. And… there is no way to predict
how good a given pack will be– two manufactured at the same time may give dramatically different service
life. IF your pack seems to be "running out" too soon (radio range drops, sails won't stay trimmed maybe
in less than 2 hours), have it checked by someone with a discharge/ recharge capably battery charger.
D. Lithium Polymer Cells (LiPO)- Lithium Polymer (LiPO), and Lithium Ion (LiFE) Batteries are
newer technology than NiMH batteries. These types of batteries require a specially-designed charging
and monitoring systems, designed specifically for them.
1. LiPO batteries have a lot of capacity at about ½ the weight of NiMHs, but are much more
expensive than the other types. Overcharging LiPOs, or charging them at too high a rate, or
when they are charged in enclosed spaces (like your boat) can cause them to burst into flames.
LiPOs also have a higher voltage output per cell– 3.7, so a standard 2-cell LiPO pack is 7.4 V.
Servos will last a significantly shorter time at these voltages, unless they are "high voltage" servos.
Ditto for receivers- buy one suitable for 8 volts. Even better- don't use LiPOs in your sailboat.
LiPOs are not recommended for any but the most careful, expert RC sailor.
2. Lithium Ion Batteries (LiFE) have a lot of capacity at the same light weight as LiPO’s, but
without the downsides. LiFE batteries do NOT have the charging sensitivities or risks associated with
LiPO batteries, but still require a different type of charging system than a "standard" battery
charger.
LiFE Batteries are generally 3.0 volts, so they (a 2-cell pack at 6 volts) are OK with any standard servo
and receiver. LiFE batteries are recommended for the sailor who wants the lowest weight, and best
performance, OR where there is a very high load such as with large, digital sail winches.
This graph depicts the typical performance pattern for various cell types
The “time” line would depend on many factors– efficiency of the battery pack, heat of the day, drag on
the system (such as how smooth your sheets travel), wind strength, and others.
Type
Develop
“Memory”?
Lose Voltage over
time of life/ charge
Recharging
capability
Available
Capacity/mAh
Voltage per cell
Alkaline Dry
Cells
NiCD
NA
Yes
No
2400
1.5
Yes
Yes
100s
600
1.2
NiMH
No
Yes
75-100 times
700– 3000
1.2
LiPO
No
No
Approx 400 times
1000– 3000
3.7
LiFE
No
No
Up to 1000 times
1000– 3000
3.3
F. So- enough already!!! what do we recommend?? What do you need? You
technically only need one good rechargeable battery pack, but it pays to have a spare if you plan on sailing in a
weekend regatta. Change battery packs at lunch. You need 6 volts to run the sail servo/winch in wind
speeds over about 5 MPH, so …
…you should consider a basic 6V NiMH 5-Cell Pack and a "peak" charger, capable of adjusting
output at (say) .5, then 1.0, to 1.5 volts.
-
OR -
....If you are buying an all-new system, anyway, purchase LiFE battery packs, and the
associated charger. The 2-cell LiFE pack would weigh about 4.6 oz. as compared to a typical 5cell NiMH pack at 5.4 oz., or about the same as a 4.8 v 4-cell pack used for light wind conditions.
Sources to purchase batteries, chargers etc.:
Hobby Shop
Local Hobby Shop
HydriMax HCAM 6351 6.0V pack– 5.4 oz. 5-cell flat pack
2000 mAh
$ 25.00 - $ 30.00 plus tax each; no shipping
Tower Hobbies
www.towerhobbies.com
HydriMax HCAM 6351 6.0V pack– 5.4 oz. 5-cell flat pack
2000 mAh
$ 24.99 plus shipping
CheapBattery Packs.com
www.cheapbatterypacks.com
Elite 1500 6.0V pack– 4.5 oz. 5-cell flat pack; 1500 mAh
$ 15.00 plus shipping
I like to order a NiMH 5-cell pack spec’d as follows from Cheap Battery Packs.com
5 X A123 NiMH Elite 1500 cells. Flat Pack, 22 Ga wire, HiTec Male plug. 6V, 1500 Mah pack,
weight is 4.5 oz.
These packs, with either analog or digital servos will give me 5 hours of sailing. So far, the 5 -8 packs I have
experience with have lasted great, then I sold them with boats. Going to a higher-capacity cell (ex: 2000 mAh)
costs $ 1.25 more per cell ($ .25 X 5), BUT on a normal sailing day, after 12 races, 2-1/2 hours, in every wind,
I still have OVER 6 volts remaining in my battery pack.
These recharge (at 1.2 amp charge rate) in about 35 minutes after 2-1/2 hours of sailing. (Meaning I used 400
mAh for 2.5 hours sailing).
VI. Battery Charger: Some basics:
A. You never want to discharge your battery pack below about 1.0v per cell. So, a 5-cell 6v
pack should never be used below about 5.0 volts. You can check your voltage after using a pack, by
either a voltmeter/ multi tester, or a voltmeter sold for RC use. Here's an illustration:
Typ. Voltage fully charged
Typ. Voltage after sailing
Minimum recommended
6.0 v
5.0 v
(5-cell pack)
7.5 v
B. To manage all this: You need a decent charger. See chart below. Useful features are:
1. adjustable output
2. an indicator (light or sound) when the battery pack is fully charged
3. the ability to use at home (AC input) and in the car (DC input.)
Don't buy anything but a “peak” charger– one that senses when your batteries are approaching a
full charge, and reduces the charge rate to a trickle or "off" entirely. Don't use a battery charger
designed for a car or your garden tractor. They will overcharge and ruin your battery pack(s).
Basic charger
Recommended Charger
THE Charger
Wall Charger– often comes with the There are many in this category- one
radio. “Dual” chargers have two
is:
outputs– one each for the radio (TX)
and one for the Receiver (RX).
DynoCharger Prophet Plus $ 35- 40
Hobbico Accu-Cycle Elite
$150
A cycling charger. This one
- peak-charges and discharges.
- records data about any of (up to) 10 packs, and
“remembers” the charge rate for each.
The one that come with a Spektrum Charges one 4, 6 or 7-cell NiMH pack - Digital read-out lets you see each pack’s
DX6i (transmitter AND receiver
(NOT for LiFE, LiPO, or rechargeable capacity– so you can accurately predict the hours
package) charges at 150 Mah– .15
TX packs).
on the water before you have to change packs.
amps. Wall Chargers are NOT
-Charges 2 battery packs at the same time.
"peak" chargers.
Works on AC wall plug OR 12V (have - AC/ DC (must add car charging plug)
to change the alligator clips over to a
- From .2 to 2.0 amp adj. charge rate
A wall charger takes awhile –put the car plug). Peak detection means it
Normally use this charger at 1.2 amps rate. It
pack on charge Friday night for a
senses as the battery pack becomes
Saturday race. The Spektrum wall
fully charged then backs off to a trickle should recharge a pack used 2- 3 hours (400 mAh
used) in 15 - 20 minutes.
charger (150 mAh) should recharge a charge.
pack used 2- 3 hours (500 mAh used)
Annual Battery Pack Reconditioning: also- the
in 2.5 - 3 hours.
Charges at 1 amp, 2, or 4 amps.
Elite will discharge your pack.
The 2 and 4 amp charge rate is
DO NOT LEAVE YOUR
TOO MUCH for any packs you will
- discharge the pack to about .5 volts per cell (3.0
BATTERY PACK(s) ON A WALL use!! Be careful. Use 1 the amp rate.
volts total) ONCE per year; then
or ANY) CHARGER FOR
- recharge it a .2 amp rate.
EXTENDED PERIODS.
This charger (at 1.0) should recharge a It will (assuming a 1500 mAh pack and .5 volts/
pack used 2- 3 hours (500 mAh used) cell) recharge in about 5 hours. Thenin 30 minutes.
- set the charger to "discharge (to 1.0 v/cell = 5v)
then recharge"
It will tell you the capacity of the pack under
those conditions- that is, fully charged to
discharged down to 5 volts; example- it might say
the 1500 mAh pack "took" 1420 MA. At 250 MA
usage (typical), you would have up to 5.6 hrs.
sailing.
Tips:
Keep a dry boat- FIX leaks!!! Never store it with the hatch on.
Corrosion X sprayed on the connectors will prevent moisture damage and corrosion.
Charge your battery pack IN the boat. Many on/off switches have a third lead that hooks to the
charger.
One good value is the Prophet Plus charger– under $40 at a hobby shop.
For any of the recommended chargers, you will also need leads to hook to your pack, and a car plug
(Radio Shack) so you can replace the alligator clips leads that come on the unit.
Once a year, after the sailing season is over, fully discharge your battery packs (probably you will have
to plug into the boat, and leave “on” until it runs flat—3 to 4 hours). Then at a SLOW rate– .2 amp or
less- fully recharge the pack(s).
Test the capacity of your packs: If you know what your servos and RX draw, run it flat again to calculate
how many Mah’s your battery pack will charges to. Example– say your boat draws 300 Mah, and it takes
6 hours to run completely flat;
= 300 * 6 = 1800 Mah capacity. NOTE: even a great pack loses something through its
connections– so 85% of rated capacity- .85 * 2000 = 1700 Mah would be decent for a 2000 Mah
pack.
Install a voltage indicator in your boat. These are inexpensive ($10-12), somewhat inaccurate, but a
good indicator of your state of battery charge. They are at least as accurate as your fuel gauge in the car!
Winter:
1. At the end of the sailing season,
a. Clean all connections, use a plastic brush (like a toothbrush, OR a plastic wheel brush on your
Dremel.
b, Charge, then discharge ALL your battery packs. Then recharge fully. Come back and top it off in
January, then once more in April.
Use a discharge battery charger. Charge the battery to full, then discharge to a level of 1 volt; the mAh
discharged is the capacity of the battery pack. If you do this through 2 -3 cycles, you should see the total
capacity increase (more mAh discharged getting to the 1 volt).
Store your boat and all battery packs indoors, not on a concrete floor.
Good sailing!!!