DIY DC-to-DC Chassis Battery Trickle Charger (Trik-L-Start Alternative?)

You've probably heard that the Trik-L-Start DC-DC battery trickle charger has been discontinued, the only commercially available alternative is the Echo 15-Amp Charger by Xantrex. The Echo Charger is quite expensive at around $150 and only compatible with lead acid batteries.

I wanted to add a chassis battery trickle charger from my Solar Charge controller's auxiliary output but couldn't find an inexpensive low current DC-DC trickle charger for my application. The Trik-L-Start trickle charger would have been ideal, but they are no longer sold, necessitating the DIY approach. With the addition of a battery protection module to the circuit, it will mimic the Trik-L-Start trickle charger and can be adjusted to start/stop charging depending on the source voltage.

Above is the schematic diagram for the Lead Acid Battery Trickle Charger. The first module is to activate/ deactivate the boost converter/charge controller depending on a set voltage threshold. A battery protect module is required for direct coach to chassis battery trickle charging; without it, the charger will be constantly drawing from the coach battery to charge the chassis battery. The battery protect module will not be required in my application because the solar charge controller's auxiliary output is only active when there is a surcharge current from the PV panels.

Key Features:

1. Allows chassis battery charging without voltage drop while maintaining isolation at all other times. Independent battery banks should be isolated in absence of charging voltage to prevent discharge between banks. 
2. The Lead Acid chassis battery can be fully charged/maintained by providing the correct charge voltage profile. In contrast to "diversion chargers" such as Trik-L-Start or Xantrex Echo, this has a multi-stage charging circuit that is independent of the other charging source. 
3. The threshold voltage to enable and disable the charger is user adjustable, allowing it to work with either lead acid or lithium battery sources.
4. Ease of repair; a faulty module can be easily replaced.
5. Because it's cool if you make your own.

Supplies you'll need:

• 12V Battery Charging Controller Protection Board Module (I have not tested this board and cannot vouch for its dependability or performance).
• 12V to 24V 5A/120W Step-up Power Supply (While 3A can be used, the 5A version is preferred)
• 3A Lead Acid Battery Cell Battery Charger Module
• 16- gauge wires
• Project enclosure and (optional) Cable Gland
• Inline ATO fuse/ holder or similar
• 16-gauge Butt Connectors or 16-gauge Spade Connectors (depending on how you wire it)

Tool's you'll need:

• Wire stripper and Terminal/Connectors Crimping Tool
• (Optional) Ferrule Crimping Tool / Ferrules
• Variable voltage power supply or similar (to properly set the disconnect/reconnect set points on the battery protection board). Some Battery Protection Modules include a built-in voltmeter for setup; you may not need a variable power supply with those- search them up on Amazon.

Depending on the coach battery voltage, the Battery Protection Board Module can be set to reconnect or disconnect the load (12-volt to 24-volt Boost Converter). Typically, for lead acid coach batteries, set to connect at 13.6 volts (charging source is active) and disconnect at 12.8 volts (fully charged battery without charger). It will be different for Lithium batteries and depending on the charging source settings.

The Lead Acid Battery Charger Module is a multi-stage charger, it bulks charge till battery reach around 14.8 volts (per manufacturer) then it switches to float mode (13.55 volts). Power source requirement is between 15-28 VDC (Recommended 16-25 VDC) hence the need for 12-24 volts Boost Converter.

Here's mine without the battery protection module. It is not required in my application because the charging source (solar charge controller auxiliary output) is not always active. The charger output is wired directly into the chassis battery post and protected by a 5-amp inline fuse. I also added a dash-mounted inline switch from the solar output to the DC-DC trickle charger so I can remotely disable/enable it. It's been a few months, and the charger keeps the chassis battery charged. 

NOTE: To prevent shorts, there is an acrylic separator between the boost converter metal fins and the battery charge module. If you include the battery protection module, you may need a larger project enclosure.