Finding and measuring hidden electrical loads.

[William42483]

Hi Pippi. Hi everyone. My question is electrical in nature. Electricity isn’t my strong point-lol. I’ve watched several YouTube videos (starting with Pippi’s) about doing energy audits of your power consumption and I understand the process. The question is about finding hidden or phantom loads on the power system.

I am a weekender (also a newbie) and want to expand my RV trips into longer stays. Most of my camping is boondocking, and I have no generator–yet. My rig is a 1978 22 foot class A Winnebago. (Yeah, it’s old, but it’s my first and I got her for a song. I named her Waltzing Matilda) In doing my audit, I come across a few items that I can’t figure out how to measure. For example, the bathroom fan in the roof vent. Someone please educate me/confirm the technique with the multimeter to measure the amp draw for that?

Now my bigger question. I can’t access my water pump without removing a large cabinet from the interior of the RV. I can’t even see it, but the location of the fresh tank and the sound when the pump operates give me a pretty good idea of where the pump is located. How can I figure out the amp draw of the pump? I tried emailing the nice folks at the Winnebago factory in northern Iowa, ( my home state) but the rig is so old that they have limited info on my model.

Any words of wisdom would be appreciated.

BTW, my battery bank is a pair of group 27 (12 Volt) batteries hooked in parrallel to give me about 200 amp/hours. I plan to add a third group 27 battery this year. That will give me a (theoretical) capacity of 300 amp/hours. According to what I have been able to learn on YouTube, 50% is a deep discharge so that would mead 150 amp/hours. Adding a margin of safety, I figure 100-120 amp/hours of realistically usable power available. I also have an older group 24 battery that came with the rig. I carry it and keep it charged, but I will only hook it up if the regular battery bank is dead. (Something I haven’t had to do as yet.) Next year, I want to add a 150 watt solar system to help extend my power capacity.

[OldJohnT]

To measure current draw you need an “ammeter” its a pass through series device that either hard wires in the circuit in between the source and the load or can be an induction or clamp on unit that works by placement in contact with the conductor or has a horseshoe type loop placed around the conductor. A cheap multi meter which is good to measure voltage or resistance (ohms) may or may not have an “ammeter” feature. If so, one lead connects to the source and the other to the load. One place to series tap into a circuit may be where the DC power distribution panel is located and the fuse to that load is located. Often the nameplate on say a furnace blower motor or a vent fan etc states the current but such is often not visible. Another way where its easier to attach and use an ammeter is right at the battery and you would have to have all loads EXCEPT say the fan in question isolated and OFF and then be able to turn the fan on and off and read the current draw.

That 300 Amp Hours of battery energy storage is a decent start for dry camping although I consider 12 volt so called RV/Marine batteries as semi or quasi deep cycle compared to true deep cycle 6 volt golf cart batteries. 300 battery Amp Hours and 200 watts of solar is a good what Id consider a minimum start. Unless size and location is a problem its no harder to install say a 200 watt panel versus only a 100 and four Trojans would give you the 450 Amp Hours I get by fine with.

John T Retired Electrical Engineer in Indiana

[William42483]

Thanks John T. I appreciate the very helpful info. I have now added the third group 27 battery and my battery box is full, so If I were to add more or go to golf cart batteries, I’d have to rebuild it or build a new one. That isn’t something I’m prepared to do at this point. I have read much about the golf cart batteries and they seem to be a better long term choice for energy storage. )Read that as greater storage capacity and better longevity/lifetime of the batteries with deep cycling.) For now, I’m going to stay within budget and keep my 12 volt batteries.

My boondocking trips are usually only 2-3 days and I am judicious about my electric use, so I don’t anticipate a problem. I’d like to add solar, but maybe next year-lol.

I have replaced all the interior lighting with LED bulbs which are rated at about 3 Watts as opposed to the original incandescent ones that used ?? Was it 10 or 30 Watts? I don’t remember exactly but I do remember thinking that I could now run every light in the interior simultaneously and use the same amount of power that just 2 of the old ones used. (not that I’ll ever be using all the lights at once-lol.) I also never run electrically powered heating appliances (such as a Mr. Coffee) unless I’m hooked to shore power. Since my favorite boondocking spot is only 20 miles from home, I usually don’t even bother to put the frig on DC power while driving back and forth. I just fire it up with the propane once I arrive. Last year, I did fine with just my 2 batteries, (never took them below 11.5 volts and that was only once.) but I wanted to add the third for piece of mind.

Yes, I have a digital multimeter. It’s a cheap one from the big box store, but it does have a DC amps measurement function. I have never used that function and I appreciate you schooling me a bit. I’ll give it a shot and see what I find out.

The roof vent fan is easy enough to get to for measurement right at the fan motor. For the water pump, I’ll probably go to the battery box as you described.

Now thinking about the solar, what do you think of one of the 150 Watt briefcase systems I see advertised? Do they function as advertised or are they really just junk? I understand that most often, we get what we pay for, but on some of the higher end items we pay a lot just for the brand name without any real increase in quality. So the cheapest version is out as is the most expensive. Somewhere in the middle is usually where I go. I’m looking to spend about $500 next year on a solar supplement system. Do you think that is realistic?

Thanks again for the advice.

[William42483]

P.S. I’m looking to extend my trips from the current 2-3 days to stays of 4-6 days. Not huge and I could probably do just fine with what I have, but…

I want a nice piece of mind/safety margin where my battery bank is concerned.

[OldJohnT]

William, two friends have those fold up suitcase style portable solar panels AND THEY WORK GREAT. Here’s their HUGE advantage (if you are there and take a minute or two a few times a day) they can be kept at the maximum harvest angle and kept pointed direct to the sun UNLIKE a flat roof mounted unit ESPECIALLY if you have maybe a 25 ft or so extension cord for extra portability. HOWEVER Id use a good heavy gauge say 12 Gauge cord to reduce voltage drop. In my experience a 150 watt portable panel, if you move it a few times a day for the best angle to the sun, will harvest as much as say 300 watt flat rooftop mounted panels. One minor disadvantage is they usually come equipped with a cheap PWM solar charge controller which doesn’t work quite as efficient as a slightly more expensive MPPT solar charge controller but that’s nothing too much to worry about.

YES $500 budget (if you self install) is a good solar start. I bought my last three 235 Watt panels for 90 cents per watt, but I spent around two hundred bucks for a 4 stage MPPT Smart solar charge controller.

No problem with your present batteries, I’m ONLY saying if you ever upgrade and go bigger Id opt for true deep cycle golf cart batteries (like Trojan T -105 at 225 Amp Hours or equivalent etc)

Good luck and best wishes

John T Long retired electrical engineer

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