Ivynovich Posted June 14, 2020 Share Posted June 14, 2020 Hello! Brand new to the forum. Brand new to RVing. I just bought a 1990 Toyota Dolphin yesterday. It’s a beautiful rig but the previous owner made a number of mods to suit their needs and they don’t exactly suit ours. Namely, they removed everything LP, though the main line/fixtures are still there but we now have a 3.2 cu ft mini fridge and no stove. Eventually we may convert it back, but we need to leave on a trip relatively soon so we’re going to attempt to run the fridge off the battery through an inverter and I have some questions. I’ve spent all day trying to figure this out how to make this setup work for us. I think, based on some research, that I’m going with a pure sign wave 1200w inverter. - The battery is on the passenger side under a bench but sealed inside a box. Wires come out of the box and attach to two silver things with small terminal posts (see picture - I know little about electricity other than what the internet has taught me in the last 12 hours, so I don’t know what those are called.) Can I wire the inverter to those things? If so, which of the four posts is positive and negative? If not, how do I connect the inverter since the battery is inside that box? - While driving, with the alternator give enough power to maintain the battery level enough to run the fridge? - There is just one 12v battery installed. Would you recommend adding a second battery? If so, I then have questions about where to install it and how to connect it to the original battery? Does the new battery need to be in a similar box? Could I somehow open up that box and make it bigger? Im sorry for so many questions. This forum has already been a helpful resource for me. I know someone on here named Zero had some posts about running a similar Igloo fridge on an inverter and being able to get a couple days out of a single battery charge, so, Zero, if you’re reading this, help me out Quote Link to comment Share on other sites More sharing options...
fred heath Posted June 14, 2020 Share Posted June 14, 2020 Those appear to be inline circuit breakers. All 4 posts are “hot”. Was probably installed to protect the coach battery(s) from power surges. If you’re not familiar with electrical circuits best to get some help from someone who is. Quote Link to comment Share on other sites More sharing options...
Derek up North Posted June 14, 2020 Share Posted June 14, 2020 Yes, those are 'circuit breakers. Like fuses, they are sized (# of Amps) to protect the wires are installed in. If too many amps pass through a wire for its diameter, the wire will heat up and could cause a fire. Like fuses, do not be tempted to install a higher rated circuit breaker to 'solve' a problem. Before embarking on an electrical 'journey', I suggest you buy a cheap 'compass' (multimeter aka VOM) and I've attached 'maps' (wiring diagrams) for the Dolphin. The diagrams aren't the easiest to read but the best I've found online. Quote Link to comment Share on other sites More sharing options...
Derek up North Posted June 14, 2020 Share Posted June 14, 2020 The circuit breaker will be marked with it's rating (Amps). This one happens to be 20A. Quote Link to comment Share on other sites More sharing options...
Maineah Posted June 14, 2020 Share Posted June 14, 2020 Here is the deal with inverters every 120 volt device you connect is a draw on the battery by a factor of 10, so 3 amps of AC fridge converts to a power draw of 30 amp on the battery. Quote Link to comment Share on other sites More sharing options...
Ivynovich Posted June 14, 2020 Author Share Posted June 14, 2020 (edited) Thanks for the responses. This is starting to make some sense. Maineah: can you tell me if I’m thinking correctly? If my fridge is rated at 65w, 115v, that equals .56 amps (=65/115). Based on what you say, I then need to multiply that by 10, so it will draw 5.6 amps from the battery. Obviously there is a surge in wattage when it starts up which is hard to account for, and the fridge only draws when the compressor is running. So say my single group 24 battery is 50 ah but I don’t want to discharge more than half, that leaves me with 25 ah to use. if I run the fridge continuously, 25ah/5.6amps = 4.4 hours that I can run the fridge if the compressor were running constantly. Assuming it runs half the time, I could possibly run it for 8-9 hours on a single charge. That’s assuming Only the fridge so the water pump and lights may drain a bit as well so it will end up being less than that. We will be boondocking but doing a lot of driving so my theory is that we can recharge the battery while driving and then keep the fridge running for 6-8 hours when stopped. Am I understanding this correctly? Is my math correct? Also, does the size of the inverter matter in terms of its power draw, or does it only depend on the load? For example, if I put a 100w load on a 1500w inverter vs. a 1200w inverter, do they draw the same power from the battery or does the bigger one draw more even though the load is the exact same. What I’ve read is that it is the load that matters, but can you confirm? Edited June 14, 2020 by Ivynovich Deleted picture Quote Link to comment Share on other sites More sharing options...
WME Posted June 14, 2020 Share Posted June 14, 2020 Your basic math is good, but it is not going to be enough in the real world, so make it "gooder". A simple change is more battery. Check your battery box and see what will fit. A gp 24 has around 60-70 AH. A gp27 has about 20% more AH, a gp 31 has about 35% more. Check the internet for actual sizes. A proper solar panel setup, if you dry camp for 2-3 days, will save a lot of engine running. If you only camp for 1 day then drive to the next stop, then this is not so helpful. A 2000w inverter generator A pure sine is about 90% efficient and a modified sine is around 75%. The actual draw difference between a 1200w and 1500w inverter is negligible. What is more important is idle current. How much it draws when its plugged in but not running anything. Quote Link to comment Share on other sites More sharing options...
Maineah Posted June 14, 2020 Share Posted June 14, 2020 Modern inverters are pretty efficient it is the power draw so if you have a 2K watt inverter that's saying it can produce 2000 watts AC from a battery so at that rate it's 20,000 DC watts if the load is 20 watts that's 200 watts at the battery. Run time is important is your original fridge toes up? There is huge amounts of energy in a 20 LB propane tank if the original fridge works beyond a doubt that is the way to go on gas. Boondocking with a dorm fridge needs some backup small generator or solar. They make some very nice chest type coolers but for the price it's better to just replace the propane fridge! Quote Link to comment Share on other sites More sharing options...
Ivynovich Posted June 15, 2020 Author Share Posted June 15, 2020 Super helpful, so thanks for your responses. The previous owner pulled the propane fridge (and the whole LP system, but the pipes are still there) so we don’t even have it. I’m on a bit of a time crunch as we want to leave in a week on a trip from MN to Maine so trying to come up with a solution to get us through this first trip, then can consider reinstalling propane. If we can come up with a used propane fridge in short order we would consider that. I’ve definitely considered the options WME lists above. The battery box is big enough for just one battery - are you aware of any ways to expand the battery box to allow room for a second battery? Buying a 2000w portable generator is our current fallback if indeed this setup isn’t going to work...so it seems like that is what we’ll need to do at least for now. Quote Link to comment Share on other sites More sharing options...
Maineah Posted June 16, 2020 Share Posted June 16, 2020 It will work if you can stand the noise. If it never had a generator there should be at least a large compartment that might be a place for more battery power. and maybe a small generator like a Honda. Quote Link to comment Share on other sites More sharing options...
Ivynovich Posted June 29, 2020 Author Share Posted June 29, 2020 In case people are curious, running the mini fridge of the battery/inverter has worked out quite well. We’ve done a lot of driving (MN to Maine coast and now making our way back west) so the battery had ample opportunity to charge and we were able to run the fridge the whole time we were driving and, except for 1 exception, whenever we stopped. The longest we ever stopped was probably 8-12 hours and I don’t know exactly how much battery life it was draining because I have yet to buy a voltage meter. Makes me think seriously about keeping the electrical setup and getting a bigger battery bank to better support boondocking vs. switching back to propane. Thanks for your insights to help me get started! Quote Link to comment Share on other sites More sharing options...
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