Modifying battery in use on a day/night solar vent.

Thread Starter

SierraLima

Joined Sep 13, 2022
2
Greetings everyone,
So I live in a reasonably humid area and I own an enclosed trailer. The trailer has a Marinco N20804S solar vent w/ overnight battery (https://www.marinco.com/en/p/n20804s). I'm currently keeping it under covered parking when not in use which obviously means the fan on the solar vent isn’t circulating the air for long after I park it in the shade.
I’m looking to modify it to be able to run for extended periods of time unattended as an addition to it’s normal capability. What I have in mind is to have a switch and an external battery plug that switches it from using it’s internal 2.5Ah 4.8V NiMh battery (https://www.marinco.com/en/p/n20890) and to be able to be powered by an external 20Ah (or more) 12V SLA battery. This large SLA battery will not be charged by the solar cells and I’ll charge it at home with a battery tender or something along those lines.
According to the specs, the unit can run for about 24 hours on the internal 12Wh battery, so power draw is roughly 500mW. So with a much larger 240Wh battery it should run for about 20 days or almost 3 weeks. It’s a reasonable expectation I will tend to it every few weeks and recharge the large external battery so that should suit my needs.
I thought about just using a much larger NiMh battery, but man are those things pricey. Even still I can’t find one with near that watt hour capacity at 4.8V so I’d realistically need to wire several large 4.8V NiMh batteries in parallel to get the endurance I need.
I called the support people at Marinco and they wouldn’t divulge any technical details about the specs on the solar array, the fan motor or any of the electronics and they had no desire to help me modify the unit so I have very little to work with. I was initially thinking of maybe just connecting the SLA battery directly to the motor and circumventing the solar cells and charging/control circuitry but without knowing the specs of the motor, that doesn’t sound like a brilliant idea.
Since I’m just a lowly software engineer and just an electronics hobbyist, I’m not 100% sure the implications of swapping not only battery chemistry but also voltage. So I figured regarding voltage, a simple 12V to 5V (close enough to 4.8V) DC transformer should do the trick. Since SLA and NiMh batteries don’t charge in the same way, my plan was to simply use a diode to ensure that even if there’s sunlight on the solar cells it can’t charge the SLA battery since the current can only flow one way, effectively eliminating this concern.
Is there any reason this won’t work? Are there any factors I’m unaware of? Anybody have any better ways of solving this?

Thanks,
Omri
 

Ya’akov

Joined Jan 27, 2019
6,550
Welcome to AAC.

Your goals seem reasonable though your chosen method may not be the right way to go about it. Do you have photos of the device disassembled with both sides of the PCB(s) well light and sharp focused?

The first thing that strikes me is that you may not want to bypass the NiMH battery but instead the solar panel and let the device charge the internal battery from your SLA. But in any case, that's just surmise without more information.
 

Thread Starter

SierraLima

Joined Sep 13, 2022
2
Hi Ya’akov. No, unfortunately I don't. The PCB is not easy to get to and remove from what I saw. I think a lot of the parts of the vent are glued and not bolted/screwed together. It is pretty easy to get to the battery and it's leads, which is one of the reasons I was leaning towards replacing it on the battery end.
 
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