How to add a DC to DC charger to an existing solar setup?

[drabina]

I have a simple solar system in my car that consists of one 100W solar panel, Victron 75/10 SCC and Li-Time 50Ah battery. The system is used to run a 12V refrigerator when I am out on weekends. So far, the system works fine but I would like to add the ability to charge the battery via alternator when driving. Sometimes I drive 2-3 hours one way to or between the destinations. This driving time could be used to charge the battery in case the weather is not cooperating to use the solar panel. What would be the simplest and budget friendly option? I am looking for a permanent solution (hardwired) and would like to avoid stuff where I have to manually connect the DC charger, switch some wires or flip switches. Unless of course we are talking $$$$ vs $$.

 

[45North]

Simplest is to unplug your panels and plug the battery into your vehicle's cigarette lighter plug so it can be charged at 12vdc.
Alternatively you could just plug the frig itself directly into the cigarette lighter plug while you're driving (don't they already come with a cigarette lighter plug for this reason?) And then replug it into your solar when you stop driving.

 

[drabina]

Simplest is to unplug your panels and plug the battery into your vehicle's cigarette lighter plug so it can be charged at 12vdc.

By plugging in you mean directly? No DC to DC chargers? I know the battery has BMS but would that handle bulk/float aspects? I have SCC that handles all the logic when using solar panel. I would think charging via alternator should use some equipment in the middle as well.

 

[fratermus]

What would be the simplest and budget friendly option?

IMO:

The simplest solution would be a voltage-sensing relay. Maybe $45.
The most budget friendly would be a continuous duty solenoid. $30?

Alternator charging setups work automagically, with the exception of intentionally manual setups a few people use out of sheer stubbornness.

the DC charger,

If you want DC-DC charging instead of a relay-based setup the minimum cost will be ~$100.

In all cases I recommend a way to disable alternator charging on demand in case you ever want to.

 

[mikefitz]

Connecting the litime lithium battery to the vehicle battery via a relay of some sort is not recomended. The 50Ah lithium has a recomended charge current of 10 amps, and a maximum of 50 amps, thus some current limiting device is needed.
The most versatile DC to DC available is the Victron Orion tr Smart,

Victron Energy Orion-Tr Smart 12/12-Volt 18 amp 220-Watt DC-DC Charger Isolated | eBay

Manufacturer‎Victron Energy. Models are available up to 400W and unlimited multiple units can be connected in parallel to increase output power. Suitable for high temperatures up to 55°C with a full rated output up to 40°C.

www.ebay.com

This is a charger, not just a DC to DC converter. It automatically detects when the alternator is charging and converts to a suitable charge profile for the lithium battery.


There are alternative DC to DC converter/ chargers to consider, one example,

12V 20A DC to DC On-Board Battery Charger

The best 12v battery charger. Free shipping. The DC-DC Battery Chargers are the most effective method to charge your home batteries from the starter battery

www.renogy.com

Unlike the Victron unit, Renogy charger needs a enable signal to function, making a more complex install.

 

[drabina]

So if I were to get the Renogy 20A DC to DC charger and connect its output to the battery (with solar from SCC also connected directly to the battery) it would be ok, correct? One 100W solar panel produces up to 5.5A, the Renogy DC to DC outputs 20A and the Li-Time 50Ah battery has 50A maximum charging current. So 25.5A < 50A and all should be working right if my math correct. Any issues with such approach besides having two boxes instead of one that combines SCC and DC to DC charger?

 

[mikefitz]

Any issues with such approach besides having two boxes instead of one that combines SCC and DC to DC charger?

No issues, the chargers 'play nice' together. The 100 watt panel , with a MPPT controler , has a maximum output of 7.4 amps at a charging voltage of 13.5 volts in theory. In practice around 5 amps would be typical.
The Renogy charger, although attractive with the low cost, may not be as reliable as the Victron product.
Note the Renogy unit needs a 'alternator charging', D+, signal, to operate.

 

[drabina]

Thank you all who replied. I will get the 18A Victron 12/12V charger and connect it to my setup. I guess the biggest project would be running wires between the car battery that's up front and the LiFePO4 I have in the back of the car. I may also look into upgrading the battery from 50Ah to 100Ah.