Inverter Nightmare

[smithmv]

Here's the picture: 700 watt inverter, 10 ft 8awg cable run to bat, max fuse 30 amp, bat are 2 yr old grp 24 starters fully charged but only one is attached 2 the inverter (typical 2 battery setup). Ran phone chargers, radio, flashlight charger just fine. Hooked up a 6oo watt mini 4 cup coffee maker and disaster struck. Right away the low voltage alarm on the inverter went off and it began to surge with the coffee maker turning on and off. Stopped after a few seconds checked everything. Since it was an undervolt I attached a 6 amp charger to the single battery and tried again. This time blew the 30 amp fuse. Will a deep cycle Group 27 help. Since the boat system was on "using the voltmeter", any chance I could have damaged a system/or worse yet something in my motor "salt water series sx 200"? I checked every thing, even engine fuses and everything was fine. Last point, By passed the single max amp fuse box and ran the coffee pot, same low volt alarm but no surge. Noticed the bat voltage dropped rapidly to about 10.5, the undervolt voltage point. At that point I quit while I was behind. Thank for any help. RT

 

[WillyBWright]

Re: Inverter Nightmare

Inverters don't do heating well. That will be in the booklet you got with the inverter. It'll do microwaves, but not heating elements.

 

[JB]

Re: Inverter Nightmare

I see no mention of a Yamaha or Suzuki outboard here. This must have been intended for Electrics.

 

[jlinder]

Re: Inverter Nightmare

1. 700 watts would draw about 60+ amps on a 12 volt system.<br /><br />2. 600 watt coffee maker can have surges that are higher than 600 watts.<br /><br />3. 30 amp fuse should have blown very quickly.<br /><br />4. On land, 8 awg would be rated for only 40 amps.<br /><br />5. You bypassed the fuse without knowing why it blew? Not a good idea. Didn't neccessarily damage anything, but not a good idea in any situation.<br /><br />6. Sounds like you have nothing putting current into the batteries when you do this. Draw 60+ amps from any battery and expect a voltage drop. Run it through 8awg wire and expect more.<br /><br />7. You don't mention it, but do you have 8awg wire on both the positive and negative lines to the battery? If not, what is the negative return line wire?<br /><br />8. Suggestion - get a small stove. For heating it will make life much easier and trouble free.

 

[31900]

Re: Inverter Nightmare

I must agree with Jack. To expect to run a 700 watt inverter on a single battery is folly especially when your cabling is inadequate. If the inverter is to deliver 600 watts it is probably drawing close to 60 amps (so much for your 30 amp fuse)allowing for losses within the inverter. There will be a considerable voltage drop on your cables and the battery will be flat in no time at all. It just won't work. Get a small camping stove that uses throw away gas. cans.

 

[18rabbit]

Re: Inverter Nightmare

Something isn’t adding up here. A typical coffeemaker draws a couple amps at most.<br /><br />A problem is with a battery’s discharge rate, not the battery’s capacity. The faster you discharge a battery, the less you can get out of it. A battery’s amp/hour specs are derived from a steady discharge over a 20-hr period, or a discharge of 5% per hr. Flooded cell batteries have the least performance for high-amp discharge (and charging). They are considered unacceptable if the discharge rate exceeds about 20% of the battery’s capacity. Hit a flooded cell group 24 with a 60-amp load and you get a few minutes of power from it. “Few” as in single digit. AGM batteries perform much better in these situations.<br /><br />A 700w inverter has the potential to draw 64 amps at 12vdc IF you create that load.<br />700w / 120vac = 5.83amps<br />700w / 12vdc = 58.3 amps<br />58.3amps (12vdc) x 1.1 = 64.1 amps. This figures in 10% for inverter inefficiency.<br />64.1 x 5 = 320.5amp battery capacity is the ideal minimum to support the inverter’s potential loading. But you will see that loading only IF you hang a 700w demand off the inverter.<br /><br />Your typical coffee maker uses a couple amps at most, usually less.<br />2amps x 120vac = 20amps x 12vdc = 240watts.<br />20amps (12vdc) x 1.1 = 22amp load on a 12v battery.<br /><br />To keep the battery’s discharge rate within 20% you would need<br />22amps x 5 = 110a/hr battery.<br />You could squeak by with a group-27 battery for running a typical coffee maker, but a group-31 would be better, and a group-4D (or a pair of group-24’s or 27’s) would be best.<br /><br />A 600w coffee maker isn’t typical. I’m guessing you have an espresso machine???<br />600w / 12vdc = 50amps<br />50amps x 1.1 = 55amp load on a 12v battery.<br />55amps x 5 = 275a/hr of battery support to get your coffee/espresso from that machine.<br /><br />Waeco makes 12v appliances. Their 8-cup deluxe coffee maker has a 200w load.<br />200w / 12vdc = 16.7amp load on a 12v battery.<br />16.7 x 5 = 83.5amp battery capacity should support this deluxe coffee maker. That would be just above the capacity of a group-24 battery, but well within the capacity of a group-27.<br /><br />Without considering the wiring, your problems:<br /><br />(1) Get rid of the 600w coffee (espresso?) maker. It’s weird. Get a normal coffee maker, something closer to 200w.<br /><br />(2) You are using a starting battery for a deep-cycle application. No good. You need deep-cycle battery support for an inverter, AGM preferred if you are hanging an invert off of it.<br /><br />(3) A 5-amp charger is too small, especially after you get the amp/hr support needed for that inverter. Just as you should be keeping the discharge rate around 20%, so should you be charging deep-cycle batteries around 20%. That means for 700watt inverter you want around 35amps (at 12vdc) from a charger, minimum.

 

[smithmv]

Re: Inverter Nightmare

Jack L and others, thanks for your help. Big learning curve. Can you give me some help calculating Amp hours consumed at 50-60 amps(inverter pushing 600 watts) for a 5 min run. I came up with 6 amp hours burned. Have replaced aging grp 24 dealer cheapies with a grp 31 heavy duty deep cycle for the house battery 105 ah and 185 reserve,and the same dual purpose similar ah etc for starting. Also dropped to 6awg on the run both wires. Also 80 amp wide blade. What chance I kicked any unwanted voltage someplace I shouldn't have. Bat set up is parallel.

 

[jlinder]

Re: Inverter Nightmare

60 amps for 5 min would be 60 x 5/60 , or 5 amp-hours. (5/60 is the portion of the hour you ran it).<br /><br />Also, 6awg wire is rated for 60 amps. Your setup can run at that and over. I would have gone for 4awg or better.<br /><br />A big problem with 12v and high amperage runs is voltage drop in the wires. With the 6awg wire, 10 ft. from battery to inverter, then 10 ft. to get back, you should only lose about .5v in the wires. Still about 5% of your power though.

 

[bw12]

Re: Inverter Nightmare

I just took a look at my 12 cup Braun coffee maker. It says "900 watts", so 600 watts is not unusual. It may be only running for five minutes, but if the battery is too small, the voltage will drop too much, and the inverter will shut down. Therefore, using 18rabbit's formula, you will need a 275 amp hour battery. Even two 105 amp hour group 31 batteries connected in parallel may not work. <br /><br />A coffee maker is a "resistive" load and therefore should not draw more power what the label says, except maybe for an instant when it is turned on. Most inverters have a peak rating, which is typically what you see on the prominent (i.e. boasting) label. They also have a lower continuous rating, and this is the one you should use for a coffee maker. For example, I have a 300 watt (peak) inverter that is rated at 250 watts continuous. Using a similar de-rating, your inverter may only be rated for 580 watts or so continuous.

 

[18rabbit]

Re: Inverter Nightmare

Capacity is just part of it. A group-24 battery has the capacity to brew your coffee. But that doesn’t mean you can get it out of your battery.<br /><br />This is for a 72-lb Rolls battery. It is within 1/8 inch of a group-31 battery. Your battery will not perform like this one, nor did your bat cost as much. Here’s an idea of the capacity-to-load numbers for a high-end, 108a/hr group-30 battery:<br /><br />5.4amp load can be sustained for 20hrs, yielding 108a/hrs.<br />6.8amp load can be sustained for 15hrs, yielding 102a/hrs.<br />9.2amp load can be sustained for 10hrs, yielding 92a/hrs.<br />15.0amp load can be sustained for 5hrs, yielding 76a/hrs.<br />21.0amp load can be sustained for 3hrs, yielding 64a/hrs.<br />28.0amp load can be sustained for 2hrs, yielding 55a/hrs.<br />39.0amp load can be sustained for 1hr, yielding 39a/hrs.<br /><br />With a 39amp load, this high-end, 108a/hr battery effectively becomes a 39a/hr battery. That’s why I said your group-24 starting battery only had a few minutes with a 600w (55amp) load. A starting battery doesn’t want to go deeper than 10%. That Rolls battery will cycle down to 80% discharge.<br /><br />That gives you an idea of why boats with inverters have ‘banks’ of batteries. By increasing the available a/hrs you increase the load the inverter can handle without crashing the batteries. You not only need the a/hrs (capacity), you also need access to them (discharge rate).<br /><br />You don’t want to cycle your battery lower than 50% discharge. Doing so can damage your battery. Your new group-31, 105a/hr battery will provide you with 52.5amp IF you don’t hang anything more than a 5¼-amp load off of it. That 600w coffee pot you want to plug in will hang a 55-amp load on the battery. My tarot cards tell me you have about 15 (maybe 20) minutes of 600w coffee pot time before you have a dead battery. You don’t want a dead battery. Dead battery = damaged to new battery. By adding a second group-31 battery in parallel, you will have between 2 and 3 hours of 600w coffee pot time. You won’t be brewing coffee that long but more importantly, you won’t be damaging the batteries, either.<br /><br />If you want to go with just a single group-31 battery, I suggest thinking about that 600w coffee pot. A 300w coffee pot would take twice as long to brew, but you could hang it off that group-31 without a problem. Just don’t replace it with a Braun. BW12 tells us they are even weirder.<br /> <br /><br />Shhhh, don’t tell the guys with trolling motor but all this stuff applies to them, too. Not the coffee pot, the deep-cycle battery’s discharge rate thing.

 

[bw12]

Re: Inverter Nightmare

A quick search of the web suggests that any manufacturer's 110 volt AC coffee maker (Mr. Coffee, Bunn, Black & Decker, Krupps, Braun, etc.), will need from 575 to 1000 watts, depending upon the brewing capacity (4 to 12 cups). This is not surprising because these household appliances were designed to brew quickly. Your only option for low power might be a 12 volt unit, which, at 200 watts, probably brews a lot slower.

 

[cjones4@hvc.rr.com]

Re: Inverter Nightmare

This is interesting because I recently read on another board where guys were complaining that you could die of thirst waiting for coffee to brew with the 12V units. The recommendation over there was to use an inverter and an AC unit. Just the opposite of where this thread is going.<br /><br /> I guess I'll stick with my Thermos for now.

 

[smithmv]

Re: Inverter Nightmare

Thanks for all the support. A final question or two. On a 20 ft run, round trip, what is the voltage drop between 8 or 6 or 4 gage wire. Bigger the wire less resistance correct? How much real power (amps) are lost in the change from 4-6 or 6- 8? RT

 

[18rabbit]

Re: Inverter Nightmare

Use the Wire Calculator here.