Advice for making DIY starter battery charger from solar DC

[electroniclearner820327]

Hi,

I have a solar setup in my van. Briefly...300w solar, epever tracer 4215 bn solar charge controller, 105ah lifepo4 battery. Common items connected to fuse block.

I know that buying chargers is relatively cheap, at around £30, however they come with things I don't want like being a power pack and other such undesired bells and whistles. Since the system is DC, rather than buy an inverter I have already connected my laptop and phone directly to the fuse block, with their relevant voltage step downs so I thought why not also do the same with this?

I thought why can't I just make a connection from the fuse block and run it with crocodile clips to the battery. Are there any particular warnings doing this?

I asked on a solar forum about doing this and got mostly ridiculed being told I was overcomplicating and overthinking a perfectly simple solution of just buying one and that they would to pay to watch me blow myself up. Not very supportive comments and I found that extremely narrow minded to be punished for experimenting. I thought perhaps a dedicated electronics forum might be more encouraging in this regard.

If the system is 12v do I have to regulate the amperage going to the battery from the fuse block? I don't understand what would dictate the current in this case because from what I have read the devices dictate how much power is drawn normally so what would happen in the case of a starter battery? Not knowing this I decided to buy a step down device which is variable voltage but is 1.5 amps, I believe, so if I set the voltage to 12v then the amps should charge steady into the battery at around 1.5 right?

The reason I thought this would be suitable is the commercially available mains trickle chargers are rated at similar currents so I thought I would just try and emulate them.

Now are there any other safety considerations to doing this? I have seen that overcharging is something to be aware of. Is there a DIY way to add in overcharge protection simply/cheaply? Even without it though I am thinking that so long as I am monitoring the battery charge with mulitmeter and take it off just as it reaches, or nears, 14.4 volts it should be ok? Please let me know if not?

I know I should not leave it unattended for this reason and I wouldn't intend to. This solution is just for times when the battery goes so low as to not be able to start the engine which has happened to me on numerous occasions. There are cheap solar chargers available but I thought why not tap into the 300w/battery supply I already have available?

I wanted an off-grid solution to get the engine to start again and then the alternator would take over.