# generator to battery bank



## MMendez (Jul 31, 2017)

hello, I have a westerbeke generator on my house boat. I would like to reduce the need to rely on the generator for power. Is it possible to have a battery bank much like a solar system to store power so during the times i use the generator it will recharge the batteries so when the generator isnt in use, the boat will operate off the batery bank? I know i can simply connect a charger but my question is how to tie the battery power into the existing wiring. The boat currently has the generator as well as a 50Amp shore power connection if that helps.

Thank you for any help,

Mark


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## thehandyman1957 (Feb 11, 2017)

*Just up my Alley : )*

Well shoot, I spent almost 40 minutes typing up a great post for you. It was all done and all I had to do was put some pictures up, and when I dropped a pic on the page it missed the small drop box and completely wiped out my text.:tango_face_crying:
I don't think I have ever screamed at my computer before. Just a bit frustrating. So I took a 40 minute break, ate some ice cream and watched a Mighty Car Mods video on Youtube and now I'm ready to start all over again. I also added an add-on to my browser that actually saves my text as I write so I don't end up throwing my computer out the window next time.:tango_face_devil:

I do this for a living, and I'm the lead tech for the busiest Solar RV business in AZ. 

The first question you have to ask yourself is how much power do you need. If your thinking you would be able to run the air conditioner then we might as well stop now. They take way too much power and even a large battery bank will only run them for about an hour.

So if your not needing to run your AC then we need to figure out what you do want to run. There are a few things you have to work out after getting that first question answered. 

The only way to take battery power from the batteries and convert them to AC power to run your household items is with an inverter. And there are two types of inverters out there. One is called modified sine wave or step wave. This is the least expensive but also the least efficient and can damage more sensitive electronics. The second is called Pure sine wave, and is just like the electricity supplied by the power companies. It is a bit more expensive but is safe for anything you might plug into it. 

Some inverters are just that, an inverter that supplies power to your AC items from battery power. But there are also inverters that also charge your batteries. These are the best to get, and usually have a 3 stage battery charger that will maintain your batteries like the manufactures require. Yes, you could use a cheap charger to charge your batteries but most stand alone battery chargers are only 20-30 amps, unless you get the big monster ones, and are a single stage battery charger. 

Once you have figured out what items you want to run and how much wattage or ampage they require, your going to have to figure out how long you want to run them and how many at the same time. Keep in mind, for every amp you use on the AC side of the inverter your using about 10 amps off of the battery bank. So say for instance your using 30 amps of stuff in your boat for one hour at the same time. The power being pulled out of the batteries is going to be around 300 amps out of that battery bank for that hour. 

All deep cycle batteries are rated in amp hours at so many amps per hour. For instance, a normal pair of Trogan T-105's has a 105 amp hour capacity per pair if pulled at 20 amps per hour. That is from 12.9 volts to 10.5 which is considered completely dead. The thing you have to keep in mind is that you should never run a battery down further than 11.9 volts dc. The reason for this is that every battery has a charge and discharge cycle rating, or so many cycles till the end of life of the battery. If you deep discharge a battery you will get less cycles and less life. Not only that but if you constantly take a battery bank really low it will eventually damage that battery bank. 

The reason I bring this up is because even if you have two T-105's at 105 amp hours. In reality you only actually have about 55 amp hours of usable power in this bank or if your using 20 amps per hour you would have about 3 hours of use. And you have to understand this when your thinking about what size of battery bank you want to build and how much power you need. 

So if you had say Eight 6 volt T-105 batteries in a bank. If you were pulling only 20 amps you would get 12 hours of use out of that bank before your batteries were at a nominal voltage of around 11.9 volts DC.

Typically for us, most folks have a six to eight battery bank. But keep in mind, they are also using solar to charge those batteries and if the batteries are full, all that extra ampage from the solar can go straight to the inverter when needed to help compensate that draw.

There are 3 main types of batteries available for you. 

1. Starting battery: This type of battery has lots of thin lead plates and is designed for starting only. The thin plates allow for more energy pull at once for high ampage starting needs. For the same reason, it does not have any type reserve power.

2. Marine Starting/ Deep cycle: This battery is kinda a middle ground for those who need a starting battery that does not require a major amount of cranking amps but also needs some sort of reserve capacity. They are good for boating because they can be used to run some lights and small items for a short period of time without killing the battery. 

3. Deep Cycle Battery: These are a true long draw battery and are not suited for starting as they have big heavy thick lead plates designed to draw out for longer time periods. 

There are 4 types of Deep cycle batteries available to you.

1. Wet Cell: These are the most common battery out there. They have caps on the top to keep the water levels up and allow for gassing. The average life if used right is around 5 years. These have some benefits and pitfalls. The benefit is that they are the cheapest, and if given good maintenance will do great. The pitfalls are that they are messy. While in use, they create hydrogen gas (very flammable). They leak acid when gassing and cause corrosion on your terminals and cables, and eventually if not cared for, eat right through the connectors. You cannot use these batteries in a enclosed space. They must be vented and separate from your living quarters. You also cannot have anything that might cause a spark I.E. Electronics with relays (inverters or chargers) in the same area for the same above reasons. 

2. AGM/ Absorbed Glass Matt: These batteries have all the same charging characteristics as the wet cell battery but without all the mess. They are sealed and need zero maintenance. They can even be set in sideways if needed. These batteries have almost the same life span as wet cell batteries and can be placed in the same compartment as your inverter or charger and can be in your living space. You will have zero corrosion issues and your cables will stay clean and new looking.

3. Gel: These were the first sealed batteries produced, and used to be the only way you could get a sealed battery. But they had many issues. The first is that they have limited charging and discharging capacities. Their charge voltages are lower and they cannot except the same amount of ampage as wet cell or AGM batteries. If you do not have a charger that can charge a Gel cell battery you can irreparably damage your battery the very first time you charged it wrong. These were perfect for low draw telecommunication stations out in the middle of nowhere. 

4. Lithium: This is a relatively new player in the RV world and still has a bit of time before they are truly ready for the average use. The benefits of these batteries is that they are super light weight and can keep their true amp capacity throughout the entire charge discharge cycle. I.E. you can completely discharge this battery till it's totally dead and then charge all the way to the top. There is no half life issue like all the others. If they say it's 100 amp battery then you get 100 full amps before it's dead. The pitfalls are they are still very expensive. A typical AGM T-105 is about $149 compared to a lithium equivalent at around $ 1300.00. The other issue is that most inverters and chargers out right now cannot read the capacity of a lithium battery and it's impossible to know just how much power you have used or need to charge because the charging algorithms are completely different. It still works, but you never can know where it's at in it's charge or discharge cycle. It will take a few years before we see the inverter manufactures catching up to this technology.

So now that we have that information under our belt we can proceed. The average RV owner that wants a good system installed will get a 2000 watt pure sine inverter charger that has a 100 amp 3 stage battery charger combination. They usually will have us install a 300 to 500 amp battery bank depending on the available space in their RV. 

Please keep in mind. Batteries are heavy. The average weight is around 65lbs each. In your case your going to want to find the most center area in your boat to put the battery bank, so as to keep things balanced.

Also keep in mind that most inverters need to be no longer than 10' from the inverter. It's easier and cheaper to run AC lines than DC lines. 

There are two ways you can install a inverter to your existing AC system. 

1. 50 amp auto transfer system. In this set up you would take the 30 amp 110 line coming from the inverter and bridge the two hot legs on the input side of the transfer switch. This would allow you to run everything in the boat. The benefit of this design is that it's cheaper and easier. But the downside is that you have the chance to over run your inverter if you turn on anything heavy. And if you have a 110 water heater or a air conditioner and forget to shut it off it will kill your batteries in no time. For this reason, we don't do this type of install.

2. 4 circuit sub box powered by the inverter. In this setup we take a customer in his coach and have him tell us what he wants to run. I.E. outlets, microwave, TV etc. Once we determine the items the customer wants we then locate the circuits that run them and mark them (up to four). We then pull the wires from those four circuits out of the AC breaker box and run them to the new sub box. We then place a 30 amp feed breaker into one of the empty spaces in the AC breaker box and have that feed the input of the inverter/charger with 10/2 Romex. We then run another 10/2 Romex from the output of the inverter/charger and send that to the new Sub box. This way, the whole thing is fully automatic. If you plug in or run the generator the inverter see's this power and shuts off the inverter and starts the charger. If power is lost it then automatically turns the charger back off and starts the inverter. This is done so fast that most electronics do not see the drop and stay on.

When installing the inverter/charger we use a 300 amp T-fuse and 4/0 wire to hook to the batteries. 
Yes I said 4/0 wire.:tango_face_surprise

When wiring up the battery bank we use 2/0 wire for all interconnects. Don't cheap out on wire. If you don't use the recommended size of wire you can turn it into a welding cable in less than 30 seconds and batteries will go boom.:tango_face_devil:

Also, don't forget your grounds on the inverter and Sub box. 

So you might ask yourself, why the heck would I need a 100 amp battery charger anyway? Well, lets think about this for a second. Your generator is probably around 6000 watts or close. Your battery bank might be 500 amps in size. 

You could run your generator for 4 hours and have a completely charged battery bank or you can run a cheap charger and run the thing all day. Without actually having any other way to charge your battery, it's really the only way to go.

So I'm going to attach some pictures of some of the work I've done so you can get a idea of what your looking at minus the solar systems. This isn't a cheap solution, but its the most efficient way you can do it. If you do this right, you will have a great system that will last you years of trouble free service. 

Good luck.:tango_face_wink:


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## Osviur (Sep 7, 2015)

Thank you Handyman, this is a really complete and clear explanation with simple words and a model for the way to explain technical themes that may be difficult to understand, but you did it easy. Congratulations!


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