Charging a house battery while using it with a single stage charger. Ok?

[Freeeeeeedddddommmmm]

Hi,
I’m looking for some advice, having trouble finding the answer online...

I have just begun RV life and as I do not have a solar panel system setup yet, I’m finding my battery system a little small for the electricity requirements. So when I’m parked at a friends house, I’d like to have my mains power battery charger running while I use the electrics. I’ll add a solar panel at some stage, but in the meantime, I’m wondering if anybody can tell me if it’s safe (or not) to charge my house battery while using it at the same time with a single stage charger? Am I likely to do damage to anything in the system?

the system is:
120ah AGM battery
20A smart charger (can’t remember the brand, please let me know if it’s important I state the model)
2000w pure sine wave inverter
MacBook laptop
Basic Computer monitor
5v phone charger running from the inverter.
Engel fridge (MR40)
Arlec BC581 compact charger (single stage)
Electric Coffee grinder
Blender
Battery powered Vacuum cleaner

thanks for any input! I’m betting there are a tonne of technical pitfalls to know here...

 

[Journey]

I've done that lots of times when working on the MH when not plugged into shore power.

 

[Freeeeeeedddddommmmm]

thanks for your reply! I’ve had it plugged in for about an hour now while using the computer, screen, fridge and charging a phone, and the charge level seems to be staying where it is (about 11.5V). So I guess that means everything is being run directly from the charger? My biggest concern is, will this damage the inverter or is the charger likely to send ‘bad’ power to the appliances?

appologies if this is a stupid question! lol

 

[DonTom]

, I’m wondering if anybody can tell me if it’s safe (or not) to charge my house battery while using it at the same time with a single stage charger?

Sure, It's just not the best way, but I doubt if you would notice any difference. I know one guy whose converter crapped out and for now uses a regular car battery charger on his RV house battery when at RV parks.

I am going to install my old converter in his RV soon, since I am now using a lithium battery with an 80 amp converter.

-Don- Reno, NV

 

[Freeeeeeedddddommmmm]

Cheers Don. Makes me feel a bit better about the situation. Would hate to destroy the whole system just as soon as I start travel!

 

[Utclmjmpr]

Problem I see is a flat battery at 11.5 volts,, 12.1-2 is at 50% discharged, so if you can't "gain" on that you need to reduce your consumption until it comes up to 12.5-6 and stabilizes.. In other words your not "charging" at this rate when your taking more out than your putting back in.>>>Dan

 

[Gary RV_Wizard]

No problem at all using 12v power at the same time as charging - your converter/charger is designed to do that anyway. And if plugged to shore power, things like your laptop, blender, coffee grinder can run directly from the 120v power - there is no need to use the inverter.

However, I see a couple warning signs of potential problems. The 11.5v indicates the battery is badly depleted and not getting charged. 11.5v is essentially a "dead" battery - fully charged is 12.6v. Another is that a single 120 AH battery is nowhere near sufficient to power a 2000W inverter at even 50% of its rated power. I suspect that at times the inverter just shuts itself off when you try to power too many things or maybe a single large thing. And a 20A converter/charger isn't going to fully replenish a discharged battery in an hour or two. More like 6-8 hours to get to 80-90% and 12+ to get to 100%.

It would be helpful to know more about your electrical system and how the inverter and charger are wired in. And whether the 120v outlets you are using are always powered via the inverter, even if shore power is active. The brand & model of both the charger and the inverter would also be helpful.

 

[Freeeeeeedddddommmmm]

thank you all for your responses, I'm getting a lot from this...
So I'm in New Zealand, so that means our power outlets are 240v. Not sure if that matters, but thought it worth mentioning.

The inverter I have a switch on and off for, and turn it off when not in use. I like to watch TV in the evenings, so the computer and monitor are being run with the fridge as a main drain (as well as some LED strips).

Great to know to keep it above a certain voltage before using and charging, thank you. I understand that this is a bit of a small battery system, but unfortunately I have to start cheap. I may upgrade in the near future.

Inverter is wired in directly into the battery, I have a battery monitor with a 300a shunt also attached in line with the 12v components (fridge, LEDs), which are run through a fuse box.

The brand and model of the dc-dc charger is an

Projecta IDC25 DC/Solar Battery Charger​

Found here. Projecta IDC25 DC/Solar Battery Charger

Once again, cheers to everyone on this very helpful thread!

 

[Gary RV_Wizard]

Your 240v/50Hz mains power doesn't really make a difference. Presumably you also have a 240v/50Hz compatible charger (what make & model, if known)? I'm guessing it is in parallel with the DC-DC charger, so both can charge at the same time. The one with the higher voltage dominates the results, but it's not harmful. Without a solar panel, the DC-DC charger only gets power when the engine is running (engine alternator).

Typically the 240v mains charger directly powers the 12v needs as long as shore power is present, thus preserving battery power for later use.

Most RVs with an inverter have some sort of switching so that all the 240v stuff can run directly off shore 240v when available, but it may be yours is set up so that certain outlets or branch circuits always run off the inverter. That's OK too, except for the additional wear & tear time on the inverter.

 

[DonTom]

The one with the higher voltage dominates the results

Don't you mean the one with the highest current capacity under load?

Like when I start my RV with my new lithium battery. My charge voltage drops the battery voltage a little as the voltage of the charged lithium is higher than my RV charging voltage. The lower voltage wins that one!

-Don- Reno, NV

 

[Gary RV_Wizard]

Don't you mean the one with the highest current capacity under load?

No. The highest voltage determines which source pushes the amps in. It's tough for any battery source to beat a charger that has a 120v power source behind it and the ability to produce 14+ volts output. A solar panel might beat it out, though.

 

[DonTom]

No. The highest voltage determines which source pushes the amps in.

If the voltage doesn't drop under load, like my lithium battery does when I start my RV. Even at high RPMs. More voltage on the battery when I turn the engine off. However, I expect the opposite to happen when the battery gets discharged a bit.

-Don- Reno, NV

 

[Freeeeeeedddddommmmm]

Hi Gary, thank you for your response! Learning a lot here. It’s an Arlec BC581 12v charger.
—

I noticed something a bit puzzling today, and have another question, wondering if I should make another thread for this?

here’s the question in any case:

I noticed today that when I power on my inverter with no load, my battery monitor states that it’s drawing about 11A??? I have no idea why this would be happening... is this an obvious answer for anyone? Faulty inverter? I have no idea myself without pulling the whole system out and spending a lot of time diagnosing with trial and error...

I should preface this with saying that I have a solid basic understanding of electronics and electrical systems, and have installed and built the system myself, it’s just that some of the finer details elude me... I have an electrician friend and an electrical engineer friend, but it seems this is RV specific problems so I thought I’d ask here. (hopefully that is enough explanation to validate my qualification to do this sort of work lol).

Sorry If this is hard to read, and hopefully I’ve described the situation adequately... I know my communications are a bit unclear at times...

 

[Freeeeeeedddddommmmm]

P.S. thought of a couple more details that might be pertinent to the situation: I have a multi board plugged into one outlet, and the computer monitor to the other outlet of the inverter. The multi board has a circuit breaker on it. The 11A draw reading on the battery monitor is with the breaker in the off position, but still plugged into the inverter (it’s difficult to get to the inverter to unplug from that end). Noticed that if I unplug the computer monitor from the screen end, the battery monitor shows 34A draw??? This would indicate to me that it’s Something to do with how I’ve wired everything together or maybe it’s because the inverter is not ‘in-line with’ the battery monitor so it’s reading incorrectly?

Do I need to draw a circuit diagram to describe the situation better?

 

[Freeeeeeedddddommmmm]

Could it be that: Any power that is being drawn outside of the circuit that is in-line with the battery monitor shunt will throw off the reading. And that makes for bad readings on the battery monitor, and the battery is not being drained this quickly? I am unsure how battery monitors work...

 

[Gary RV_Wizard]

I noticed today that when I power on my inverter with no load, my battery monitor states that it’s drawing about 11A??? I have no idea why this would be happening... is this an obvious answer for anyone?

An inverter does draw power even if no load, and a bigger wattage inverter draws more than a smaller one. Probably not 11 amps, but the monitor measures all amperage in/out so there is always more than you realize. LP detector, CO detector if you have one, circuit boards for appliances, etc.

Could it be that: Any power that is being drawn outside of the circuit that is in-line with the battery monitor shunt will throw off the reading.

The monitor can only "see" current that is passing through its shunt via whatever Positive and Negative (ground) wires are connected. Without a detailed wiring diagram showing what circuits are connected thru the monitoring circuit, we could only guess.

 

[Gary RV_Wizard]

If the voltage doesn't drop under load, like my lithium battery does when I start my RV. Even at high RPMs. More voltage on the battery when I turn the engine off. However, I expect the opposite to happen when the battery gets discharged a bit.

Don't over-think this, Don. At any given instant, there is a charging source and a battery. If the charging source is higher voltage than the battery at that instant, current flows into the battery. Maybe slow, maybe fast, depending on the differential. If the charging source is less than the battery voltage, no current flows in from that source.

The original question was even simpler - two charging sources coming together at the battery terminals. As far as the battery is concerned, it's all one source (whatever volts/amps appear at the terminals) and the voltage seen there will be the voltage from the higher source. Amps will flow in proportion to the voltage differential between battery and the source, limited by whatever the source(s) can provide.

 

[DonTom]

. If the charging source is less than the battery voltage, no current flows in from that source.

Yes, but can that lower voltage load down the higher voltage? I would say yes, just like putting a weaker battery in parallel with a stronger battery. And such seems to happen in my RV charging.

But I have to admit, this is confusing to me, yet seems so simple.

I was wondering what would happen in my RV when my new lith battery was charged above the charging voltage. I found this confusing, but not sure why. So I did the experiment just to see what will happen as I watched my SmartShunt. The battery drains with the extra charging. I turn off the ignition to stop the drain and then get a positive charging (because of my solar).

Does all this sound correct to you?

-Don- Reno, NV