A DIY Alternate Battery for Heng Long Tanks

[keilau]

My Heng Long tank power system had been 3 pieces of Maxamps.com 7.2 volts NiMH pack and a Duratrax Piranha Digital Peak Battery Charger. The Piranha allowed pretty quick charging of the packs and gave actual capacity reading. When all 3 Maxamps packs died and a replacement pack costs $68 each, I know that I have to do something. (Yes, I am aware of many $15, 3000 mAh packs on Amazon which may be very good.) I was never happy with the discharge curve of the NiMH where the voltage drops too fast. I want to try something different.

I found a $17 recipe resulted in a 7.4V, 5000 mAh pack with a flat discharge curve. The ingredients are:
1. 2 EBL brand 26650 Lithium Ion cells.
2. 1 dual cell 26650 SMD battery holder.
3. 1 large Tamiya connector from the dead NiMH battery pack. Or a pair of XT60 connector cables.



I sawed off the 4 plastic tabs on the side of the battery holder to make it fit the Heng Long battery bay. The soldering is simple. I am switching over to XT60 connectors, but the Tamiya work just fine too. It is more expensive and more difficult to find. The pack below was made earlier.



The EBL 26650 cells are very cost effective for this application. It is cheap at $5.50 a cell when buying 4 or more on e-bay. It holds the full 5000 mAh it specified. The current capacity is a mere 4A continuous and 8A peak, but is perfectly adequate for the slow moving Heng Long with a pair of smallish 380/390 motors. I tested the premier brand Keepower cells with 15A/30A and protection circuit which is $15 or more per cell. It makes no difference to how the tank operates. And the taller Keepower cells are more difficult to fit into the holder.

The Lithium battery needs a different type (constant voltage) of charger than NiCD/NiMH which stops charging when individual cell reaches 4.2 volts. I use the Nitecore Intellicell or the SkyRC iMAX B6 mini charger. Overcharging Lithium Ion or Li-Po cell will shorten their life or even damage the cell.

[Rubicon99]

My Heng Long tank power system had been 3 pieces of Maxamps.com 7.2 volts NiMH pack and a Duratrax Piranha Digital Peak Battery Charger. The Piranha allowed pretty quick charging of the packs and gave actual capacity reading. When all 3 Maxamps packs died and a replacement pack costs $68 each, I know that I have to do something. (Yes, I am aware of many $15, 3000 mAh packs on Amazon which may be very good.) I was never happy with the discharge curve of the NiMH where the voltage drops too fast. I want to try something different.

I found a $17 recipe resulted in a 7.4V, 5000 mAh pack with a flat discharge curve. The ingredients are:
1. 2 EBL brand 26650 Lithium Ion cells.
2. 1 dual cell 26650 SMD battery holder.
3. 1 large Tamiya connector from the dead NiMH battery pack. Or a pair of XT60 connector cables.



I sawed off the 4 plastic tabs on the side of the battery holder to make it fit the Heng Long battery bay. The soldering is simple. I am switching over to XT60 connectors, but the Tamiya work just fine too. It is more expensive and more difficult to find. The pack below was made earlier.



The EBL 26650 cells are very cost effective for this application. It is cheap at $5.50 a cell when buying 4 or more on e-bay. It holds the full 5000 mAh it specified. The current capacity is a mere 4A continuous and 8A peak, but is perfectly adequate for the slow moving Heng Long with a pair of smallish 380/390 motors. I tested the premier brand Keepower cells with 15A/30A and protection circuit which is $15 or more per cell. It makes no difference to how the tank operates. And the taller Keepower cells are more difficult to fit into the holder.

The Lithium battery needs a different type (constant voltage) of charger than NiCD/NiMH which stops charging when individual cell reaches 4.2 volts. I use the Nitecore Intellicell or the SkyRC iMAX B6 mini charger. Overcharging Lithium Ion or Li-Po cell will shorten their life or even damage the cell.

What about just going with a standard size 6 cell sub “C” 6200 mAH 7.2v NiMH battery pack or two. I run this brand in some 5000 mAh packs and their cells are pretty decent for the price. 5000 or 6200 is A LOT of running time even with upgraded motors.

[keilau]

What about just going with a standard size 6 cell sub “C” 6200 mAH 7.2v NiMH battery pack or two. I run this brand in some 5000 mAh packs and their cells are pretty decent for the price. 5000 or 6200 is A LOT of running time even with upgraded motors.

There is nothing fundamentally wrong with the 6 cells sub-C pack. The DIY Li-Ion pack has some advantages:

1. I can charge them faster.
2. The discharge curve is more flat keeping the tank faster longer.
3. It can be cheaper.
4. It holds charge longer when on the shelf.
5. Li-Ion has more recharge cycles than the NiMH and degrades slower.

The disadvantage:
1. It takes some soldering work.
2. It looks less net or professional.

[keilau]

I decided to build the Lithium Ion 2S battery pack using 4 18650 cells. The EBL brand cells cost $2.54 each in lots of 4 or more. They hold over 3000 mAh easily. The cells in parallel double the capacity. Total cost per this 6000 mAh pack is about $12 in material, plus your own elbow grease.

I do not have a spot welder, but a 40-45 watts soldering iron works very well. You also need a hot gun or a hair dryer. Other material needed are nickel strip, heat shrank wrap, JST-PH connector for balance charge, wires. I use XT60 connector for power because the Tamiya connector is getting expensive and hard to find.

The finished pack fits the Henglong battery compartment perfectly in length and has plenty of room around it. In addition to the EBL pack, I also made one with Orbtronic cells. They are high drain (10A/18A) cells selling for $11 each. The EBL pack has plenty of discharge rate margin for the Henglong. The 6000 mAh gives the tank plenty of run time and keeps the velocity (voltage) till near the end of the charge. The premium Orbtronic cells do not have any performance advantage.
https://www.orbtronic.com/18650-batt...top-high-drain

You can find many video on YouTube making Li-Ion pack. It is the battery of choice for high energy density and safety over Li-Po. Some video use very good practice and some do not. Use common sense to develop your own best process.

[Nfafan]

Awesome post! Hope many others chime in with DiY battery ideas. I'd like to someday re-config my tank so that either the charge connector is easily accessible without opening the tank, or, the battery pack disguised as "mass pile of rear deck stowage".

[keilau]

Awesome post! Hope many others chime in with DiY battery ideas. I'd like to someday re-config my tank so that either the charge connector is easily accessible without opening the tank, or, the battery pack disguised as "mass pile of rear deck stowage".

The battery packs I made give the tanks 2 hours of running time which I like. With the SkyRC iMAX B6 mini at 2 amp charge current, it takes 3 hours to recharge them. It is better done during the day that I can check on them now and then.

Using the USB balance charge cable that comes with the Henglong tank, it will take 15-16 hours per charge.

BTW, I like my SkyRC iMAX B6 mini charger very much. It is cheap, has lots of options and information on the battery under charge. It costed me $37 at Amazon. Not quiet fast charge enough for tank meets, but perfect for home use with multiple packs. It helps keep the battery healthy and last longer.

[UltraVargen]

This all looks super scary to do, yet very interesting!

I'm thinking about soldering a deans connector directly to one of my Admiral LiIo batteries, so it can plug directly into my Heng Long 6.1 MFU. I'm already afraid to ruin the battery.

[keilau]

This all looks super scary to do, yet very interesting!

I'm thinking about soldering a deans connector directly to one of my Admiral LiIo batteries, so it can plug directly into my Heng Long 6.1 MFU. I'm already afraid to ruin the battery.

The Lithium Ion cells are very easy. But soft LiPo pad are a different story.

The trick is to use nickel strip. Wet the battery terminals and 2 spots on the nicke strip first. Also solder the wire to the nickel strip, not the battery terminal directly. With some practice, you can do it very quick and safely with a 40W plus soldering iron. The pre-wetted solder melts so quick that the battery are very safe. It will even better if you have a spot welder. Go to YouTube to see some video that can give you confidence.

I use XT60 instead of Dean's which is much easier to solder the heavy gauge wires on.

[UltraVargen]

Much appreciated keilau ! I'm not ready to completely build my own batteries, but it's valuable advice for the future!

[keilau]

I finally made 2 packs using the 26650 cells. Cost per pack is $10 plus hardware. They charge up to 4500 mAh using the B6 charger.

[keilau]

I finally made 2 packs using the 26650 cells. Cost per pack is $10 plus hardware. They charge up to 4500 mAh using the B6 charger.

I bought 4 more EBL 26650 to make 2 more packs. The cost including hardware is about $12 per pack which is an excellent value. The EBL cells are rated 5000 mAh per cell which is the correct rating when charged to 4.2 volts or more. My SkyRC B6 charge programs the 2S Li-Ion to charge to only 8.2 volts for longer battery life, thus the 4500 mAh, which is a prudent recommendation.

High quality Japanese/Taiwanese 18650 Li-Ion cell (3000 mAh or higher) all but disappeared from the retail market. Cheap Chinese 18650 often rates itself 9000 mAh or higher, but struggles to hold 900 mAh.

I just received my newly purchased Heng Long Sherman (3898-1), and was pleasantly surprised that HL switched to XT-60 power plug. The tank comes with a dual 18650 battery pak that holds 1100 mAh when charged to 8.2 volts. In early HL days in 2000's, this will be called premium battery, Haha.

[SoCalBobS]

I use the stock batteries.......for testing on the workbench! Otherwise, Admirals work well.

[keilau]

I use the stock batteries.......for testing on the workbench! Otherwise, Admirals work well.

The Motion RC Admirals pack uses high quality Taiwanese 18650 to get the rating. Considering the sky rocketing li-Ion cell cost, the Admirals is quite a good deal.

The Heng Long stock battery comes with a balance charge plug and XT-60 allowing it to be charge to above 1100 mAh every time, giving the tank good run time. It is not a bad option. Much better than the old HL NiMH pack.

I made my own pack for the satisfaction of DIY. The cost saving is a nice bonus.

[ArmorBolt]

I use the stock batteries.......for testing on the workbench! Otherwise, Admirals work well.

I bought a Heng Long T-34 and it came with a 1800 Li Ion 2s. I don't think it is enough to run long time. What do most people use, NiMh or Li Ion 2S or 3S and what capacity, is there any recommendation battery to buy. Thanks.

[keilau]

I bought a Heng Long T-34 and it came with a 1800 Li Ion 2s. I don't think it is enough to run long time. What do most people use, NiMh or Li Ion 2S or 3S and what capacity, is there any recommendation battery to buy. Thanks.

The Heng Long stock battery comes with 2 Chinese made Li-Ion cells which has about 1100 mAh. Older HL battery are 6x sub-C NiMH cells of about 700 mAh. I do not like NiMH battery because it self discharge too fast (not holding up charge well in storage) and the voltage drops too fast during use. I explained in Post #4 why I prefer Li-Ion cell the best, but they are getting difficult to get because of the EV industry suck up the raw material supply. The OEM HL Li-Ion pack allows 25-35 minutes runtime which is not too bad.

I no longer recommend running HL tank with 380 or 390 motor even the high voltage, low rpm kind using 3S battery because they simply heat up too fast and too much. If you upgrade to a gearbox with 550 motor, the 3S battery may be a possibility.

I have heard good things about the Admirals brand 2S Li-Ion packs with 2 cell or 4 cell. The spec are only slightly overstated. They use high quality Taiwanese cells to get the spec. The ones with Tamiya plug were sold out. Hope that they will have XT-60 packs soon. This Admirals battery are exclusive at MotionRC.