Viofo A139 pro // mobile power

[Müller]

Hello.

For powering purposes one might consider these battery-boards. I use several of these for various devices. Reliable items.

WONDOM | STORE

store.sure-electronics.com

These boards are meant to be used with Lion (4,2V)-cells. They do NOT charge LiFePO4. But there´s no problem in using PO4 for only-discharging purposes and charge them externally. Which is what i do because especially the A123 are superior cells to Lions. Much better in cold environments, much faster to charge, much more cycles especially when charging them to "only" 3,5V instead of 3,65V. Forever-cells ...

For Lion: The board charges the cells, balances the cells during charging and watches the cells during discharge-mode down to 2,8V, then cuts the power to the load so the cells are well protected.

For LiFePO4: No charging allowed! The board watches the cells down to 2,8V, then cuts the power to the load.

The boards show how much kerosine is left:



When swapping discharged cells to fresh ones (not charged by the board internally) the boards have to be activated once to deactivate the 2,8V undervoltage-protection lock. This can be done with any voltage-input above 5V. Just connect for a sec. and you´re gtg. And yes, a switch would be more comfortable ...





For these boards, a connector-kit is available. I always order board AND kit. It´s a dream-team.

WONDOM | STORE

store.sure-electronics.com

The A139 connects like this:



With the A123 the 139 is active (4k, no parking mode, max. bit-rate, constant recording) for about 8hrs. (But: you have to have a bit of an eye on matching cells, means a cell with a high internal resistance hiding between 4 other cells with a low resistance can shorten the -ON-time of your device significantly because this one cell reaches the 2,8V faster then the other ones and triggers the undervoltage-lock.

When you want to use 26650 Lion-cells which have about double the capacity of the A123 you might get into the range of 12 to 15 or more hrs. I haven´t tested.



The naked boards might find a home in such or similar housings:

 

[Dashcamuser007]

Nice kit. How long is the charging time?

 

[Müller]

Hello Dashcamuser007,

as i said, i do not use these boards with the cell-chemistry it is meant for (Lithium-Ion) but with LiFePO4 which i am charging externally, then swap discharged to fresh respectively just swap an empty to a fueld-up board. It is no problem to use LiFePO4 in these boards as long as these are only discharged in them. I use A123 because these cells are the more robust and reliable choice (cold environments) to Lions. Lions are "only" the best choice when your application needs a higher voltage level (with the same amount of batteries) or you need the highest energy-density in a given space. Sorry that i cannot tell you or even test the charging time for Lions in this board but honestly i actually haven´t even 5pcs. of them at hand to conduct the test you asked for. Only "a mountain" of A123s ...

 

[Müller]

Hello Dashcamuser007,

i just looked up the documentation for this board. There are charging-/discharging infos in it ...

 

[SPL15]

I recognize that PCB, I've used the 5-cell 18Vdc output version a few times for high powered Bluetooth speakers. It's sold in the USA by Parts-Express under their house-brand "Dayton Audio", Part number is LBB-5V2.

I've had some minor issues with the charging circuit though (at least on the V1 version). The Buck/boost regulator section sometimes blows up (Control IC shorts & output MOSFET shorts, then fries the series current sense resistor).
The MOSFET is sized properly for the circuit; I'm thinking it's an issue of excess gate current being drawn from the control IC (Not enough gate resistance), or the inductor is undersized for the peak pulse current & the core is saturating, possibly cross conducting?

It's a pretty simple design w/ basic passive cell balancing (ie bypass transistors across each cell). Charge circuit has a buck/boost converter for taking wide input voltage (5-24Vdc) & converting to 24Vdc (for the 18Vdc output version), this feeds a basic buck converter that both regulates for constant current during bulk charge phase, then switches to constant voltage when cells reach 4.2Vdc each.

Output regulation wise: There is no regulation, simply a MOSFET switch that connects the cells directly to the output terminals. There's voltage & current sensing on the output which allows the board to turn off the output MOSFET if current limits are exceeded, or min voltage is reached.

It likely wouldn't be too difficult to modify this board to accommodate LiFePO4 cell charging. The fundamentals are all there, it'd just be passive components changes (resistor value changes) for adjusting max charge voltage from the buck/boost converter, as well as max cell voltage for the cell balancing circuit. The only other issue for LiFePO4 cells would be low temperature cut-off for below freezing temps

Overall, a decent board for the price.

 

[Müller]

Hello SPL15,

Thank you for your insights!

SPL15: Output regulation wise: There is no regulation, [...]

At least on this BCPB4-board there´s one regulated output. The 12V/2A-one shown in the first picture of my first post and the one with the A139 connected to the board.

SPL15: There's voltage & current sensing on the output which allows the board to turn off the output MOSFET if current limits are exceeded, or min voltage is reached.

Output current sensing, yes, but this board watches each cell´s voltage down to 2,8V and uses this as the cut-off signal for the output, not a minimum 5s overall output-voltage. So the cells are well protected from deep discharge and below 2,8V, at least in our climate here, nothing much happens anymore regarding energy-output, so that threshold is quite ok. But: as usual, one bad cell (higher internal resistance) can make the whole team look bad.

WONDOM had anounced in the past to roll out a 7s LiFePO4-version of these boards but that never happened. Which is not a big deal because there are better external charging options. I use these.

- Add: the current MC3000 now has two propellers (fans) installed. The version tested in the link above, had one.



The target voltages of each cell-chemistry can be individually fine-adjusted to extend the amount of cycles. The A123 are charged to 3,5V at 3A each. This takes ~35min. A123 are great cells. Now LITHIUMWERKS (brand).

 

[SPL15]

I forgot about the regulated 12vdc output. I’ve never used it on any of my projects, so completely forgot it even existed. Looks to be a simple buck regulator, so should be relatively efficient (probably around 80 - 85% near max current output)

You’re right about the output cut-off for min voltage, it’s handled by the cell balancing IC & is on an individual cell basis. My only complaint w/ the board is w/ the cell balancing circuit, as it’s limited in how equal it can make the cells (by nature of how passive balancing works).

It’d be cool if Wondom produced a 4S version, would be perfect for this type of application to avoid needing any regulation between the cells & load, thus maximizing overall efficiency.

For winter use, since LiFePO4 struggles below 32F, I’m looking at possibly building a Li-ion pack (not sure which chemistry) to swap in when the temps are 20F & below. But I may just go w/ a cheap 25AH SLA w/ basic relay isolation to keep things super simple & dirt cheap. In the winter, I usually plug my car into a charger every night, so keeping SLA batteries charged isn’t a big issue