Need Help Charging My Batteries

[Tao Seeker]

Wow, this is a BIG subject, with lots of numbers, lots of equipment, and the dreaded job of designing circuits. I am a quick learner and very good with engineering and science, but I haven't ever touched electricity and circuitry before so this is still kind of alien to me.<br><br><font size="4"><b>My problem is this</b></font>: I want to set up a solar panel power source as well as a secondary source from my van's alternator, and my calculations are telling me that I need a charge controller that can accept over 100 amps at 14-15 volts! I can't find this, is there something wrong with those numbers?<br><br><b>How I came to these numbers</b> is I calculated the Pmax (maximum power output) of the <b>solar cells</b> by dividing their wattage by their nominal voltage. With a 400 watt solar setup that run about 14 volts, that's<b> ~29 amps at 14 volts</b>. I want to run my alternator - also about 14 volts - through the same controller, to avoid having multiple controllers on the same battery. According to research, my <b>alternator</b> likely puts out <b>50-70 amps</b>, so I will play it safe and say 70 amps. Combined in parallel with my solar panels, that's <b>100 amps</b>, and I won't buy anything capable of less than 120% of my estimated output, so I need a controller that can handle 120 amps!<br><br>Am I doing this wrong, or is there just something else I should be adding to the system to lessen the amps by increasing voltage?<br><br>

 

[akrvbob]

You are making it too complicated. Your car electrical system already has a voltage regulator that senses the condition of the starting battery and shuts off charging once it is charged. You just connect a cable from the starting battery to the house battery in the back in the van (you will want a continuous duty solenoid also, see the page on the site, How to have Electricity). The vans voltage regulator will prevent the alternator from overcharging the house battery. Then when you install your solar panels, a wire will go from the panels to the controller, and then from the controller to the batteries. The controller will protect the battery from being overcharged. So you will have two wires coming into the battery from the two sources with each sensing the state of charge and protecting the battery from overcharging. &nbsp; <br><br>At most you will need a 45 amp solar controller which will handle about 500 watts of panels, I doubt you can get more than that on top of a van. I have several friends who use the BZ500 mppt solar controller that is 45 amp and handles 500 watts of panels. Do a google search and you can find it for about $210. I have a BZ250 mppt that is a 20 amp controller that I paid $110 for, and I have been very happy with it. You want an mppt (Multi Power Point Tracking) controller. They add 25-35% more power going into your batteries. Most solar panels are a nominal 12 volt, they are actually 17 volts or more. The average controller simply looses those extra volts, but an mppt contoller reduces the volts but increases the amps. <br><br>Keep asking those questions!! the more the better.Bob<br><br>

 

[Tao Seeker]

Thanks for the insight. I don't easily get frustrated, but this electrical jargon is starting to get to me. I had read some articles which told me that charging via alternator without a controller is either highly inefficient, or potentially damaging, depending on the state of your battery (charges too fast when the battery is low and then not fast enough when it's close to full). If this really isn't a huge problem, and just an inconvenience, then I can skip on the controller for the alternator, since I am aware of the voltage regulator built-in.<br><br>Thanks again for all the help, it's good to hear advice from someone on the inside. <br>...now I just have to make sure I totally understand how to install this battery selector solenoid, but I think I do.<br><br>

 

[akrvbob]

The problem isn't that the deep cycle will be damaged directly by charging it from the alternator, but that it won't ever get fully charged. So if you aren't aware you will probably drain the battery too low which will damage it. It may never get charged above 60-70% of its capacity, only leaving you with 10-20% usable. Every time you go below 50% the battery is slightly damaged. As long as you are careful to never go below 12.2 volts, the house battery will be fine, but for most of us since the battery never gets full, it's hard to do that. Adding solar will solve the problem because the two together should always keep the battery full. Another choice is a Ctek DC battery charger which connects to the starting battery and charges the house battery off it. It is a multi-stage charger and will charge the house battery to 100%. Bob<br>

 

[Guest]

Wow...that ctek charger is $200...sounds cool but wow!<br>

 

[Tao Seeker]

I did look at chargers and controllers for a bit (confused about the difference initially). This just led to confusion, though. I think I will play it safe and make it a rule to not hook up any high power entertainment (computer, mostly) to the batteries until I have solar installed. Besides my desktop (most of my electric needs), I only have a ZuneHD (mp3 player with web browser) and some lights (LED for smart power consumption). I may keep some small power tools around to help with repairs or projects, but I have to research how many watt hours they pull.<br>

 

[akrvbob]

Sorry for the late reply. I own Ryobi cordless tools available from Home Depot and love them. I carry an 18 volt drill and 18 volt skill-type circular saw. Both work extremely well. I have a Ryobi 12 volt charger so I can charge it from a cigarette lighter plug. Very highly recommended!! Bob<br>

 

[rcm89]

Ditch the 400w desktop and go for a high-ish end notebook.&nbsp; Your battery will thank you.&nbsp; --ron, who's down to 4 notebooks now... <img src="/images/boards/smilies/smile.gif" border="0" align="absmiddle"><br>

 

[gadgetMe]

I have a 6 month old laptop. using a kill-a-watt meter , it uses&nbsp; a max of 30 watts when the hard drive is running, 10 watts when surfing<br><br>Putz<br>

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[gadgetMe]

I just checked the charger for my DeWalt 18 volt battery charger for my DeWalt chordless drill&nbsp; .....&nbsp; 80 watts at 110 volts from an inverter<br><br>Putz<br>

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[rcm89]

Putz, I've seen my MacBook Pro 4g/500g at 42w, but that was with 3 VMware instances running, each doing an OS build on different flavors of BSD...really loading it down.<br>

 

[akrvbob]

Hey, you don't have to show off that you have a Dewalt!! <img src="https://vanlivingforum.com/images/boards/smilies/smile.gif" align="absmiddle" border="0"><img src="https://vanlivingforum.com/images/boards/smilies/wink.gif" align="absmiddle" border="0"> I already know that yours is bigger than mine! I used to have a set of Dewalt 14 volt tools, and they are great tools! If you can afford them they are a better choice. True industrial tools that will last a homeowner a lifetime. But for my use the Ryobis have been great. Bob<br><br>P.S. Most of you don't know, but I consider Pondputz a good friend, and I am just busting his chops. Fortunately, I'm sure he won't do that to me.&nbsp;<img src="https://vanlivingforum.com/images/boards/smilies/angel.gif" align="absmiddle" border="0">&nbsp; Bob&nbsp; <br><br>

 

[judygirl]

<div>&nbsp;As long as you are careful to never go below 12.2 volts, the house battery will be fine, but for most of us since the battery never gets full, it's hard to do that. Adding solar will solve the problem because the two together should always keep the battery full. Another choice is a Ctek DC battery charger which connects to the starting battery and charges the house battery off it. It is a multi-stage charger and will charge the house battery to 100%. Bob<br>

<div style="text-align: left;">I know I am going to sound stupid again, but… Would this be a good option for me- without solar, and without shore power? (89 Telstar Motorhome) This is the one I found that works off the alternator:&nbsp;</div><h1 class="parseasinTitle " style="text-align: left;color: rgb(0, 0, 0); font-family: Arial, Helvetica, sans-serif; font-weight: normal; margin-bottom: 0px; margin-top: 0px; "><span id="btAsinTitle"><font class="Apple-style-span" size="3">CTEK 56-482 D250S</font></span></h1></div><div style="text-align: left;"><span id="btAsinTitle">I have an new power center/ converter with battery charger- do I still need this?&nbsp;My house batteries are maintained at approx 14.something while plugged into shore power. If&nbsp;I start up the engine, or run the onboard generator, won't it continue to do the same thing?</span></div>

 

[Willy]

&nbsp;I'd just like to chip in here regarding power tools .n such. I've got 2 main inverters, a 300 Watt and a 1200 Watt, and really prefer to use straight 115v power tools. If the amp draw is too high (angle grinder), I can just fire up the engine. Battery powered tools are okay.. but that's about it. I don't care how expensive a battery powered drill is, but it won't power through things like my 1/2" Makita hammer drill. Same goes with my angle grinder and a number of other tools. Yup, higher power draw, but things get done FAST. ..Willy. <br>