[VanGuy]

I've got a 155AH 12v house battery - charged from 2 sources:
200w solar panels
Car alternator/engine, only when the key is in the ignition.



Is there any way to tell how much power is coming from either of the two sources? I feel like after a few hours of driving, that the battery should be 100% (is that a reasonable expectation?) but sometimes that's not the case. It makes me wonder if the solar is really doing the lion's share (due to bad wiring or something...)

 

[VanGuy]

Maybe a better (followup) question:

I've got a mutlimeter and am doing a continuity reading at the two major posts/terminals of the PAC-200 Amp isolator I use to separate the starter battery and Aux/House battery.

What kind of readings should I expect for when the isolator is switched "on" and "off". (neither of my readings is "0" or "1")

 

[Chance]

I've got a 155AH 12v house battery - charged from 2 sources:
200w solar panels
Car alternator/engine, only when the key is in the ignition.

.............

It makes me wonder if the solar is really doing the lion's share (due to bad wiring or something...)

Your alternator, when engine is running, has much more capacity than the 200 watts of solar; which may give you around 10 Amps when sun is out. Depending on your setup, the alternator may give you 10 times that much current to charge house battery. If you think solar is doing more of the work, then something is probably wrong.

 

[RDinNHandAZ]

The alternator and solar charge rate is dependent on the internal resistance of the battery being charged. If the battery is lead-acid it’s internal resistance gets very high during near charged conditions so the charging rate naturally falls. How do you know the battery is not nearly full? BTW key in ignition won’t do it the engine must be running at a rate above idle.

 

[GaryBIS]

Hi,

When your isolator is on, the voltage readings on the two main terminals should be the same. When its on, the relay is closed and its basically just a piece or wire connecting the van battery and house battery terminals.

When the isolator is off, the relay is open and there is no connection between the two larger terminals, so the van terminal will read whatever the van battery voltage is, and the house battery terminal will read whatever the house battery voltage is.

One way to directly check on how much charge is coming from solar and how much from the van is to use a clamp on meter that can read DC amps. Clamp it over the wire coming from the solar panel charge controller and that will read the charging amps from solar. Clamp it over the wire coming from the house battery terminal on your isolator and that will read the charging current from alternator.

If your battery is a regular flooded lead acid battery, the charging current should not be a whole lot more than 0.1 of the amp-hr capacity, so about 16 amps in your case. Charging current that are substantially in excess of this will cause more outgassing and will damage the battery. If its an AGM battery it may be able to take somewhat more charging current. So, your alternator may be rated at 150 amps (or whatever), but if you actually get anywhere near this, it won't be good for your battery. The clamp meter would allow you to check for excessively (or low) charging current.

Gary

 

[Chance]

.....cut....

If your battery is a regular flooded lead acid battery, the charging current should not be a whole lot more than 0.1 of the amp-hr capacity, so about 16 amps in your case. Charging current that are substantially in excess of this will cause more outgassing and will damage the battery.

....cut....

So a battery at 50% state of charge should take about 5 hours of driving before it charges back up near full charge? Sounds bleak.

No wonder so many RVers can't wait for lithium batteries to become more affordable.

 

[RDinNHandAZ]

This is also why solar is so good. It supplies the current you choose when you design the solar system. I use about 325 Watt hours overnight (27 amp hours of my 230 Amp-hour FLA) and I can recharge it with my solar by 10 am in the sun off my 200watt solar panels if the sun is shining or in about the same time from my alternator on a really rainy day.

 

[Chance]

I agree solar is ideal choice for those who boondock for days at a time with minimal daily energy consumption.

For those with greater energy appetite, like those who run air conditioners even for short periods, microwaves, coffee makers, hair dryers, etc. then I'm not sure if solar is as great a fit. If I used 5 kWh daily, is there a practical way to get that much solar on a van's roof?

I haven't looked at solar in detail because we drive daily if not on shore power at a campground, so recharging batteries is much cheaper and faster from a converter or alternator. Our needs would have to change a lot before solar would make economic sense to me.

 

[GaryBIS]

So a battery at 50% state of charge should take about 5 hours of driving before it charges back up near full charge? Sounds bleak.

No wonder so many RVers can't wait for lithium batteries to become more affordable.

Hi,
I have two 6 volt, 220 amp-hr flooded lead acid batteries hooked in series to make a 12 volt, 220 amp-hr battery.

My batteries are from Costco, but similar to the Trojan golf cart batteries. I called Trojan (which has good tech support), and asked about maximum charge rate. I believe that she said that the most they recommended was 32 amps and that more than that would result in more gassing and shorter life. So, that would be about 32/220 = 0.15 of the batteries amp-hr capacity, so maybe 0.15*160 = 24 amps for the 160 amp-hr battery, so maybe 80/24 = 3.3 hrs from 50% to full charge, but this assumes that you get exactly the 24 amps through the whole charge process, which is unlikely -- it will likely taper off as the battery gets closer to full charge -- your 5 hours may be more realistic. AGM batteries can be charged somewhat faster.

Gary

 

[Winston]

Your alternator, when engine is running, has much more capacity than the 200 watts of solar

Yes, your alternator can theoretically deliver much more current than your solar, but it won't. The difficulty is that, as RD has often lamented, the internal resistance of your house battery coupled with "Ohm's Law". This 'one-two' punch results in a much less than expected initial charging current (from your alternator to the battery) that drops surprisingly quickly to only a fraction of this initial charging current.

So what good is a high capacity alternator if you can’t use it? Well you can - - just not charging your house batteries. Drop a ‘big ole load’ across your battery (such as our induction cooktop running a sine-wave inverter with its 150 ampere demand) and see what happens. Your alternator will come to the rescue and will supply all (or most) of the required energy.

What we really desire is a multi-stage charger that has a true constant current “bulk” charging capability . . . in our present discussion, one that supplies the maximum 0.15xAH capacity, or 24 amperes. There may be such chargers out there, but all the sophisticated multistage chargers we’ve played with fail to perform any better than simply placing your house battery across your alternator.

Ahh but solar is different. Solar, depending on how many panels you have and whether they’re wired in series or parallel, operates at a much higher voltage - - ours . . . in the order of 30 VDC. This gives the solar controller a huge advantage over your 14.4 volt alternator . . . this allows the solar controller to output its full current (or whatever lower current you may have programmed it to output) continuously until a given charge condition (like 100% charge) is reached. You can set your controller to output the maximum safe current for your battery, again in the example being discussed, 24 amperes, until the battery is fully charged.

Don’t sell your solar short. We, in fact, normally disconnect our alternator and let the solar do its thing.

But to better understand what’s going on, we like the idea of the clip-on ammeter . . . and suggest that you include a shunt/ammeter in your system so that you can see - - at any given instant - - precisely how much current your batteries are supplying or are being recharged.

 

[Chance]

Yes, your alternator can theoretically deliver much more current than your solar, but it won't. The difficulty is that, as RD has often lamented, the internal resistance of your house battery coupled with "Ohm's Law". This 'one-two' punch results in a much less than expected initial charging current (from your alternator to the battery) that drops surprisingly quickly to only a fraction of this initial charging current.

So what good is a high capacity alternator if you can’t use it? Well you can - - just not charging your house batteries. Drop a ‘big ole load’ across your battery (such as our induction cooktop running a sine-wave inverter with its 150 ampere demand) and see what happens. Your alternator will come to the rescue and will supply all (or most) of the required energy.

What we really desire is a multi-stage charger that has a true constant current “bulk” charging capability . . . in our present discussion, one that supplies the maximum 0.15xAH capacity, or 24 amperes. There may be such chargers out there, but all the sophisticated multistage chargers we’ve played with fail to perform any better than simply placing your house battery across your alternator.

Ahh but solar is different. Solar, depending on how many panels you have and whether they’re wired in series or parallel, operates at a much higher voltage - - ours . . . in the order of 30 VDC. This gives the solar controller a huge advantage over your 14.4 volt alternator . . . this allows the solar controller to output its full current (or whatever lower current you may have programmed it to output) continuously until a given charge condition (like 100% charge) is reached. You can set your controller to output the maximum safe current for your battery, again in the example being discussed, 24 amperes, until the battery is fully charged.

Don’t sell your solar short. We, in fact, normally disconnect our alternator and let the solar do its thing.

But to better understand what’s going on, we like the idea of the clip-on ammeter . . . and suggest that you include a shunt/ammeter in your system so that you can see - - at any given instant - - precisely how much current your batteries are supplying or are being recharged.

I get all that, honestly, but you're reading a lot more into my statement than was meant. Unless I'm making a simple math error, a 200 watt nominal solar panel system will likely be limited to around 10 Amps, more or less. By the time you factor intensity, angle, wiring loses, controller inefficiency, etc., I don't see how we could expect much more than 10 Amps reaching the battery; and probably less.

On the other hand, any modern vehicle alternator will be able to charge a house battery at much more than 10 Amps. A person would have to be clueless to install wiring or other limits that wouldn't at least support much more than that. For RVs, alternator equipment in the range of 50 Amps or more is not unusual.

In this case I'm fairly sure that a working alternator will recharge that battery much quicker than 200 watts of solar. My statement was simply that if he's not getting over 10 Amps from alternator (to exceed solar), then something is wrong. Like perhaps engine is not running or something is not wired correctly.

 

[RDinNHandAZ]

But it doesn’t in a real application see post #7 .
I have a diesel with 200 amp alternator, and 200 watts of solar. Charge back time is very nearly the same! Done it about 10 times. In this case what seems logical is not what nature provides. My battery to battery interconnect is fused at 80 amps so that is not limitng the charge rate. The battery is determining how much charge it will accept due to its internal resistance. This has been stated several times here. Is there another way we can say this so it becomes clear to you?
CAN is not always the same as WILL.

 

[Chance]

But it doesn’t in a real application see post #7 .
I have a diesel with 200 amp alternator, and 200 watts of solar. Charge back time is very nearly the same! Done it about 10 times. In this case what seems logical is not what nature provides. My battery to battery interconnect is fused at 80 amps so that is not limitng the charge rate. The battery is determining how much charge it will accept due to its internal resistance. This has been stated several times here. Is there another way we can say this so it becomes clear to you?
CAN is not always the same as WILL.

No, you can't. I read English just fine -- the words are clear but the meaning isn't because it doesn't hold up. Sorry but it's true.

If your battery doesn't charge faster than 10 Amps from your alternator, then you have a problem too. Or a very small or extremely crappy battery.

Repeating something over and over or louder won't make it right. Even battery manufacturers have stated that a battery should take much more than 10 Amps. Why is that so hard for you to understand? Or do you want to argue just for sake of arguing.


Batteries WILL charge faster than you are saying -- it's done all the time. I've done it too. One example is running generator for a couple of hours to power converter. Another is driving. It's not rocket size.

Just because you have a problem doesn't mean others will have the same one.

 

[RDinNHandAZ]

No problem for me. My offer to explain it in a different way was to make clear why what you say isn’t going to work. My batteries (see post #7 for size), solar, alternator and system is designed to do just what it does. It is all working perfectly and as I want it to. The output of the alternator is controlled as is the solar. The control is done by its computer regulating the voltage being applied to the battery. Overcoming that will allow lots more current into the battery and eventually ruin it. There was a discussion of DC to DC chargers earlier and they boost the charge rate to do just that. They raise their output voltage to increase the charge rate. I am not too interested in them for the reason stated.

Argue? I reread my posts to see if I was doing more than explaining. I don't think there is an argument there. I certainly am not saying anything louder. Relax, we are here to help each other. I also don’t see where I repeated “over and over” Each post I made was trying to state new ideas and introduce new information to help. Despite my comments and Winston’s (former electrical engineer BTW) you are not accepting. We disagree. No need to argue.

 

[Chance]

I'm good too. No problem, and I'm also not looking to argue.

As an engineering project manager, I spent decades designing, building, and starting up manufacturing plants and doing other projects that involved many disciplines. I usually know when something doesn't sound right even when I'm not an expert in the field. I also make mistakes and need to learn more as well, so I do listen and try to learn as much as possible.

I don't want to make this personal in any way whatsoever. Facts should speak for themselves; as they should. Getting back to OP, I would never be satisfied with +/- 10 Amps, and don't consider that unreasonable (I'm not that patient plus I use too much power). For me that would be a problem that needs a solution.

I agree that each of us has to determine what works best for us.

 

[RDinNHandAZ]

Good,
I have a degree in Physics, I have lived on batteries for 8 years off grid with a 3KW Dunlite wind plant. I have had previous RVs with solar. I have had to solve electrical problems from lightening strikes to running a house on 114V DC. I have taught electrical theory and practice. We undoubtedly have a fair amount of common knowledge.
These discussions are not about our expertise or background they are about providing verifiable assistance to the OP and to those who respond. I think the OP does not have a problem. Your comment about needing 5 hours to recharge the battery is about the rate batteries should be charged. If you push lots more charge into them (which I agree can be done) it will likely exceed the recommendation of the manufacturer.
Here is some “new” information from a major battery maker:
http://www.batteries-faq.com/activekb/questions.php?questionid=55

 

[Winston]

It does appear that the temperature of this discussion has risen to the point of eclipsing productivity. Chance, you're probably right that we 'over responded' to your point. Our comment was merely to repeat a point discussed in these threads some months ago that when one charges a lead-acid battery they may be surprised and disappointed to see that the targeted initial charge rate doesn't hold . . . that in the end, the "area under the curve" (average charge rate) will drop to half (or lower) the desired rate. In our now-retired CaRV, we used a large class 8 245AH AGM battery in the trunk and metered the system at 20 amps. We employed wire size/lengths to limit the maximum current to around this value. When the battery was low (and for us low was typically 12.5 volts), the initial charge "pinned" the meter - - we'd guess at a charge rate of 25 amperes. It didn't take but a few minutes for the current to drop to less than 20 and within 30 minutes it was well on it way to 10 amps. This was true whether charging from the car alternator or our CTEK smart-charger.

And, since we were expecting this same 'decline' with our new system, we were "surprised and not disappointed" to see how the solar panel/controller worked - - we can set the desired charge rate (at least indirectly) through a much wider range along the charging curve. (And while it is true that we are comparing apples and oranges in that we now are charging lithium, we believe the 'more constant charge current' conclusion holds across these battery types.)

By the way, that 245AH AGM battery, with just one season of use, is still available . . .