inverter displayed voltage lower than tested at battery

[griptwister]

Hello, newb here, just grabbed a new Xantrex Prowatt 2000 sine inverter and a class 31 consumer grade 115 Ah wet deep cycle battery. PLan is to use during short outages to power TV, cable box, ps3, etc. More maybe if needed but for now I only have the single battery. I really cant believe I could not find the answer to my question on the net because it seems basic. Anyway here's the deal. I hooked up the brand new inverter to the brand new battery with 2 foot long 0 gauge stranded insulated cable with copper ends pro crimped by my local battery shop. My voltage as tested at the battery terminals as well as at the inverter terminals is 12.71, but the display on the inverter shows 12.5. This is at no load with just the unit switched on. Is this normal, am I somehow having loss or volt drop ? To test I also hooked up a set of 4 gauge cables that are 3 feet long with ends I crimped on myself in my vise and I get the same exact results. Thanks in advance.

[sensij]

Hello, newb here, just grabbed a new Xantrex Prowatt 2000 sine inverter and a class 31 consumer grade 115 Ah wet deep cycle battery. PLan is to use during short outages to power TV, cable box, ps3, etc. More maybe if needed but for now I only have the single battery. I really cant believe I could not find the answer to my question on the net because it seems basic. Anyway here's the deal. I hooked up the brand new inverter to the brand new battery with 2 foot long 0 gauge stranded insulated cable with copper ends pro crimped by my local battery shop. My voltage as tested at the battery terminals as well as at the inverter terminals is 12.71, but the display on the inverter shows 12.5. This is at no load with just the unit switched on. Is this normal, am I somehow having loss or volt drop ? To test I also hooked up a set of 4 gauge cables that are 3 feet long with ends I crimped on myself in my vise and I get the same exact results. Thanks in advance.

I'll ask the obvious question... how confident are you in the calibration of the instrument that is reporting 12.71 V?

[inetdog]

I'll ask the obvious question... how confident are you in the calibration of the instrument that is reporting 12.71 V?

And I will add the question whether there might be some voltage drop in the input connection of the inverter?
Note that just because your meter displays the voltage to the nearest .01, that is no assurance that it is accurate to that level.
For a typical digital meter the accuracy on a 15V DC range could well be +/- 1%. For an inexpensive meter, make that 2%.
Now 2% of 12 is .24.
The display on the inverter cannot be accurate to better than .1V (+/- one digit) if it does not display hundredths of a volts. But it is likely that the readout was factory calibrated to have its best accuracy in the range from about 10V to about 15V.

Time for a calibrated third opinion.

[griptwister]

I'll ask the obvious question... how confident are you in the calibration of the instrument that is reporting 12.71 V?

WELL ! It is a free digital multimeter I got from Harbor Freight for no other reason than just showing up ! Ahem...Yeah... After reading your reply I went out to my shop and grabbed my OTHER older harbor freight free digital multimeter. This one matches the 12.5 reading on the inverter display. So, lets say I trusted the first meter because the result matched what a fully charged battery should be, and now I suppose I will trust this 2nd piece of junk meter because it matches the voltage displayed by the inverter. Lol. Its time for a better meter, but this is probably my issue. My question then becomes, is the voltage normally displayed by the inverter accurate as to what a correctly calibrated meter will show at the battery terminals ? I feel stupid for not knowing this as it seems basic. I have never had an inverter with a display before. Thank you for your help Sir !

[Mike90250]

old Chinese proverb
Man with 2 watches never sure what time it is.

[SunEagle]

I hope you got your voltage meter question answered.

I will bring up another thought which you should be looking at. Using a 2000 watt inverter on a 115Ah battery can quickly discharge that battery. Especially when you want to run high load electronics like a ps3, tv and cable box.

You should be looking at a smaller inverter or bigger battery or maybe run only critical electrical equipment during an outage. Low wattage lights come to mind.

[griptwister]

I hope you got your voltage meter question answered.

I will bring up another thought which you should be looking at. Using a 2000 watt inverter on a 115Ah battery can quickly discharge that battery. Especially when you want to run high load electronics like a ps3, tv and cable box.

You should be looking at a smaller inverter or bigger battery or maybe run only critical electrical equipment during an outage. Low wattage lights come to mind.

Yes I think I did. Since then I have charged the new battery for the first time and it now sets at 12.7 volts as per the display on the inverter, and also tests at 12.7 with my older cheapo multimeter. Thanks to all for the responses to my newb dilemma. So, would a smaller inverter drain the battery slower on the same load than the larger inverter, or why would a smaller inverter benefit me ? It seems it would be the same to me ? And how is a PS3 not critical in an outage ? Lol.

My back story is this; I used to have a small 300 watt inverter a few years ago and an old beat up deep cycle battery for a trolling motor that got fairly neglected. It was nice when the power went out to run my TV, on an antenna as opposed to cable because the cable is most often out at the same time as the power. That load is around 110 watts just for the tv. So, I thought I would get an bigger, better inverter that would power more stuff if I needed it to, and get a few batteries in a bank to offer longer run time. (I also have a 1957 WINCO 5 KW generator powered by a Wisconsin THD that I completely rebuilt ((the engine side)) about 5 years ago for back up power needs. My gas engine kung fu is strong, but my ac/dc electrical karate is white belt at best.) So, I am figuring out things as I go and trying to make as few mistakes in cost and time as I can. I have always been a fan of going bigger than present needs so needs can go bigger down the road. I would like to add a few solar panels at some point for charging and I have not cracked very far into the area of knowledge yet. Until then I can just recharge off AC or my generator, for short term outage needs.

So right now I am looking to add probably 3 more batteries to get around a 460 amp hour reserve. I have an old Exide fully auto charger 10/2/60 where the 60 is just for jump starts, so its a 10 amp charger. I have been reading for 2 days on this topic and I guess this would work but it would probably mean a slower charge rate than what would be best after I added the additional batteries. My budget is reasonably tight so I dont want to go overboard, or underboard for that matter as well. I may even add more batteries down the road. I think some chargers are stackable ? I have been looking at the Xantrex truecharge 2 but it is pricey. Also the schumacher SC-10030A which seems decent but more affordable ? So any tips on what size, type, brand of charger for my application would be most appreciated. Thanks again you's guys