The ultimate FT-817/818 internal battery solution (maybe?)

Ever since I bought my FT-818ND I wasn’t really happy with the internal battery. Although the FT-818ND came with a larger battery (and a better charging circuit to handle the bigger battery) it still wasn’t really up to scratch. I found that when out portable it’s useable life was really only about 1.5 hours and then it’s a pack it up and go home job. Unless you bring a spare battery or an external source, that’s the end of your outing. While my solution might not last you a full day, it should double the useable time of your radio when portable.

The problem I wanted to solve was this: An internal LiPo battery solution, that included a charge controller/bms/balance/protection circuit, and an upgrade to the internal charging circuitry to charge the battery in a 10 hour charge cycle, that’s above the capacity of the windcamp 3000mAh offering.

Virtually every single lithium based battery solution out there, pack, unit are made to a standard (14xxx, 18xxx, 26xxx round ones for example) and that standard hasn’t been adopted for use in the FT-818. If Yaesu for example had designed the chassis a little different, it’s possible they could have internally fit three, or possibly even 6 18650 batteries (or even some 26650 units) and I wouldn’t be writing this blog post.

I looked at the 18650 based solutions and honestly – I wasn’t really impressed. They required expensive cells, a custom 3d printed battery holder and a replacement battery cover. The charge controller specified to use in the units didn’t include balance charging which means as soon as the cells fall out of balance, you’re not going to get the individual cell advertised capacity, as one will always be charged less than the rest. The other readily available option is the Windcamp solution, but that solution can only be charged with the supplied charger, and requires you to toggle a switch which disconnects the battery from the radio in order to charge.

Let’s talk about charge controllers and lithium BMS boards for a minute. There are literally thousands of lithium charger boards out there. I’ve been sourcing my parts off Aliexpress, and most of these boards, quite franky, are crap. They are what’s advertised as a “protection board”, so they do prevent your lithium batteries from overcharging or over discharging, but they do this by monitoring the individual cells during charge and discharge, and if ONE of the cells goes above or below their cut-off voltages (usually 4.2v and 3.2v respectively) then they cut off the supply to the pack. During charging the cells are simply wired in series and they just hope that when one cell passes through the cut-off voltage, that the rest are close. In my experience, once a pack falls out of balance, the total capacity is severely diminished. Some are advertised as “balance” boards, and then in the fine print tell you they do NOT balance the cells, and others are blatantly falsely advertised. For my application – to do it right, I needed a protection board/BMS that had a balance charger in it as well.

So, I had two things to find, a small LiPo protection/balance charge board, that will not only protect the cells from overcharging but also balance them as they charge, and some high capacity LiPo cells that fit in the radio. Ideally i wanted the highest capacity cells I could find, and that meant bigger cells than the Windcamp 3000mAh solution.

Eventually I found the “4060100” LiPo cells, and a board on AliExpress that had a built in protection AND balance charging circuit. The 4060100 cells I used were designed for a tablet IIRC, and are rated at 4000mAh. They are rated at 4000mAh but they’re not a high-discharge lithium cell. Lithium cells are capable of some pretty insane current levels for their size/capacity. In this physical size the cells are trading off current delivery for physical size. These cells are rated for around a 5A discharge rate, which is fine for our solution given the radio doesn’t draw much more than 1A at full power at 12v. They also come with their own single-cell protection circuit, which needs to be removed for out application to fit our controller board.

The board chosen for the charge controller is identifiable as an actual balance charger (instead of advertised as one – but not) by the 3 rows of chips with a small resistor in line with the chips – these are the chips that handle the balance charging of the pack. Three of these cells fit nicely inside the radio, however you do need to remove one of the small foam strips inside the battery compartment. Unfortunately the charge controller board was around 2mm too wide to fit vertically at the top of the pack, but due to the cells only being 4mm thick there is enough room to mount the board flat ontop of the back – with one small mod to the battery cover in order for the battery cover to fit flat.

The final mod was to double the charge current by adding a second 2.7 ohm 1210 resistor in parallel with the existing current limiting resistor inside the radio, a mod which requires removing the main board of the radio to fit the resistor. My radio has been apart a bunch of times now, pulling the main board is a bit of a pain. There’s a 3 pin connector that links the main board and the PA board that’s a PITA to line up but I’ve done it enough times to be ok with it. My radio board removal is complicated by the fact I have a BHI DSP fitted to the radio as well (And I do highly recommend this mod). A small note on the charging circuit, the radio has both a “trickle charge” and a “high rate charge” circuit in the radio. The trickle charge drops around 25mA onto the battery to protect the NiMh battery from self discharge. This circuit can potentially cause a lithium battery to catch fire – as they don’t like trickle charging – IF YOU DO NOT HAVE A PROTECTION CIRCUIT FITTED. In my case because the BMS board has both over-voltage protection AND balance charger circuitry, it’s perfectly fine. Note that this mod WILL look different in the FT-817ND. There are some resources out there around how to increase the charge current on those units, it’s one of the few differences between the FT-817 and the FT-818.

So, now after the giant wall of text I’ll let the photos do the rest of the talking. The notes will be in the photos for each step.

So that’s it. a DIY 4000mAh Lithium battery solution, with an integrated balance charger, upgrade to the inbuilt charger to dump enough current into it to charge it in a single cycle, and it fits inside the standard battery compartment and the cover sits flush. It’s worth pointing out that you need a power supply of AT LEAST 12.7 volts to charge the batteries. A standard supply up to 14.4 volts from a car is perfectly fine.

Links:
4060100 LiPo Battery – https://www.aliexpress.com/item/32892267535.html
3S Balance Charger Protection Board – https://www.aliexpress.com/item/32827726118.html

73 de VK2MES