Toyota RAV4 Forums banner

pure sinewave inverter for AC power

74K views 155 replies 39 participants last post by  Templeton  
I really like the idea of using a similar system (maybe with an additional battery connected with VSR/isolator) for connecting auxiliary devices (Computer, Fridge, etc.) but I have some question that keeps bugging me.

12V Battery needs to be charged with limited current(0.1C - 0.2C) for its safety that's why I was thinking that current delivered to the positive terminal of the 12V battery is limited but I saw your post (and many similar ones) that connect loads to the positive terminal of the battery and uses the output of the DC-DC converter. How is this possible? Does the battery have an internal charging circuit that limits the charging current?

I would be very happy if there is someone that can help me clarifying this confusion of mine :rolleyes:
Thanks in advance
 
I suspect the DC-DC converter has a constant voltage output just like the alternator in a conventional gas-only car.
Since the small 12V battery in a hybrid never has to deliver high current such as starting the engine its voltage doesn't drop enough to draw high current from the DC-DC converter. Any current above normal such as to an inverter would be delivered to the added load not the baby 12V battery.
When I change mode of the car to the ready mode, I did observe 14.2V at the positive terminal of the battery (Previously it was around 12.2-12.6 V). Meaning that it could draw quite some current.

The negative terminal of the battery is connected to a sensor that regulates the charging of the 12 V battery. Here is a video that explains the charging system,
I did see this video and it was quite helpful. But what I couldn't understand is how that sensor regulates the charging system since used power is coming from the same terminal(also the same cable) used for connecting high power devices in some examples(as in this thread). I guess changing the output voltage is the only thing DC-DC converter can do to limit the charging current using the sensor readings but I couldn't observe it (the car was stationary but I don't think it changes much).
 
14.1 is a typical 12V battery charging voltage, you don't really need to regulate current. I don't have a hybrid myself yet, but on my standard car that I still drive to this day with an alternator, I've used a cigarette lighter voltmeter to see what the alternator system does. It typically runs at 14.1V for like 70% of the time, only whenever my car decelerates will it go higher for a few seconds, or if it thinks the battery is really charged up, it will drop to 12.7V sometimes whenever I'm accelerating.
You are right about charging voltage, I have no saying in that. What I don't understand is how charging current is limited when the DC-DC converter does supply around 1000W of power from that same line. (Internal resistance of the battery is almost negligible at 0.1-0.2C)

For you, why do you want a second battery? You should be fine connecting to just the one. Remember, you're not really running off the battery at all (maybe for little spikes in current), it's the DC to DC converter you're running off of.
I just want to able to run some tools even when the car is not in ready mode and don't want to risk of draining the auxiliary battery since it would still result in me being not able to run the car :D
 
I think you're misunderstanding some of the fundamentals. Charging current is limited by the voltage of the system. As the battery fills up, it can no longer take on additional charge at 14.1V. Here's a good website that explains how battery charging works, this website can teach you almost everything you could ever learn about batteries: Charging Information For Lead Acid Batteries – Battery University

The AGM batteries in the hybrid system aren't designed to cycle quickly like a typical starter battery. You really should only be running the inverter on the system when the car is in ready mode. If you want to run some tools temporarily without the car powered on, your best bet might be to look at some off-the-shelf Lithium battery solutions. Lead Acid is heavy and messy, and the hybrid isn't design to charge two LA batteries at the same time.

Hope this helps!
Thanks for both the advice and the source, I will certainly consider/check those.