Paul C. Buff, Inc. Technical Forum

Hi folks, first post.

I recently purchased the vagabond mini lithium pack. Looking for guidance on acceptable alternate charging sources. Planning to take the unit on a multi-day off-grid trip and will store unit/battery in water tight travel box and keep out of rain, etc.

By the specs, it appears one or both of these two chargers should work if wired correctly with powerpoles:

For automotive charging:
http://www.batteryspace.com/Smart-DC-Ch ... -Pack.aspx

For solar charging (choose 14.8V option from drop down):
http://www.batteryspace.com/mpptsolarch ... ypack.aspx
(see lithium side of the Specification tab on this page: https://genasun.com/all-products/solar- ... ontroller/ )

I understand that it's likely PCB would deny warranty if an alternate charger were used and the battery/unit malfunctions. I'd just like some educated opinions about any other reasons it would be inadvisable to use one or both of the above chargers for the battery pack.

Thanks!
Brendan

The 1.5A charger should work OK, though more slowly than the stock charger.

The 5A charger is a little too ambitious for the VML battery.

Thanks for the response! With that in mind I'll go ahead with the experiment and report back in a month or two.

I plan to use the first charger with a 10W panel (or car lighter socket) and the second only with a 26W solar panel, so with either charger, the solar charge current should be ~0.5A or ~1.5A max (respectively).

B

You have to be careful in charging Lithium batteries . . . the can be damaged or overheat if overcharged.

Thanks Paul.

I've received the automotive charger and solar charge controller, modified their connectors and run some tests.

Again, the charger and charge controller units are designed for 4S (series-of-four) Lithium Ion battery packs, using the CCCV method, producing up to 16.7V with diminishing current for the '14.8v nominal' 4S packs.

Also, to reiterate, the solar panels I use aren't capable of generating more than 2A at 14V+, so I am not too worried about the 5A capability of the MPTT solar charge controller at this point in time. Should I work with more powerful panels, I'll revisit the issue.

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Connections:

For both convenience and safety, I replaced the connectors on both units to use Anderson Powerpoles. The Powerpoles are compatible with the VLM system, ensure good connectivity, enforce polarity and allow me to specify different colors for the unregulated vs. regulated sides of the systems to avoid unpleasant results.

For the unregulated/solar side I chose yellow/gray to represent "solar" (e.g. yellow=sun=positive, grey=clouds=negative) and rigged the solar panels outputs and the charger/charge controller inputs with those colors.

For the regulated/battery side I used the standard red/black combination and rigged the output of the charger/charge controller with those colors.*

I triple checked all the polarities (before cutting cables, before/during installation of Powerpoles, and when energized with no load). Gotta make sure I don't let the smoke out...

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Indoor testing:

I used a variable voltage bench-top ham radio power supply set at 15V, which about what the solar panels will be generating when under load. I also used an inline V/A/W/Wh meter to track the connection between each unit and the VLM unit/battery. When powered, I see that both units' indicator lights are behaving as expected based on the input conditions and the battery charge levels. From the meter I can see that they are probing the battery state before sending significant charge current, limiting the voltage to 16.6-16.7V and tapering off the current when the voltage reaches the required peak. The MPPT solar controller also seems to be pretty conservative about the voltage drop required before which it begins the charge cycle (perhaps to avoid overcharging problems when the solar inputs are fading in and out?).

So far it looks like the chargers are playing by the rules.

Thanks for reading,
Brendan

* going forward, I'm only sourcing "12v" devices that actually accept a larger range of source voltage (e.g. 10-20V) so that they can be connected directly to 4S lithium packs if/when they aren't being used in a car: USB chargers, radios, etc. That should allow them to safely run off of the solar panels directly in a pinch as well.