Charger output at 15.5V

[Yoshimura]

The charge and float voltages of my inverter / charger have always been too high. Like 0.3V higher than the expected voltages for the selected battery type. At least, when selecting AGM1 or AGM2.

A few weeks ago, I noticed that when connected to shore power and turning the inverter on, the voltage jumps to 15.5V and then stabilized to charge voltage in the following minute.

I contacted Roadtrek and the inverter manufacturer and both suspect that is caused by a bad battery. At least, the initial voltage peak.

What do you think? Can I bad battery cause this? I did a discharge test on my battery like two weeks ago and I could draw a 5A load for 12 hours. Battery also hold charge.

Thanks!!!

[booster]

Originally Posted by Yoshimura

The charge and float voltages of my inverter / charger have always been too high. Like 0.3V higher than the expected voltages for the selected battery type. At least, when selecting AGM1 or AGM2.

A few weeks ago, I noticed that when connected to shore power and turning the inverter on, the voltage jumps to 15.5V and then stabilized to charge voltage in the following minute.

I contacted Roadtrek and the inverter manufacturer and both suspect that is caused by a bad battery. At least, the initial voltage peak.

What do you think? Can I bad battery cause this? I did a discharge test on my battery like two weeks ago and I could draw a 5A load for 12 hours. Battery also hold charge.

Thanks!!!

Where are you reading the voltage?

[Yoshimura]

Originally Posted by booster

Where are you reading the voltage?

At the inverter posts.

[booster]

Originally Posted by Yoshimura

At the inverter posts.

Does the inverter do a remote sense of the battery voltage. If it does, that could help explain the high voltage at the charger/inverter. To check what the inverter is doing you need to make sure the voltage is sensed the same as the inverter sees it as it will compensate based on that. What the battery sees, is checked at the battery.


You probably don't have remote sensing for the inverter, but might have it. If the inverter is measuring internally, about all you could do would be to clean the connections on the cables to the batteries and the ground connections to make sure they are good. It is very possible that you have failing inverter/charger, though.


If the inverter is easy to get out, you could even remove it and put it direct to a known good battery and see if it does the same thing.


If the battery has decent capacity as you tested, I don't see how it could cause a short time spike like that, but anything is possible.

[Yoshimura]

Yeah, no remote sensing. I will check at the battery however.

My neighbor lend me a battery (unknow state, currently on a tricker charger) so I could try it using jump cable.

I have a good motorcycle battery but it's small. Like 9Ah. Could I destroy it? Charge current is around 30A.

Thanks again!!!!

[Yoshimura]

Ok, I run the A/C for over 15 min on battery, turned off the inverter, connected shore power, turned on the inverter and instead of jumping to 15.5V, the voltage only raised slowly (It went from 12.5V to 14V in about 20 minutes).

So it seems the voltage jumps to 15.5V only when the battery is fully charged...

[Yoshimura]

Originally Posted by booster

Does the inverter do a remote sense of the battery voltage. If it does, that could help explain the high voltage at the charger/inverter. To check what the inverter is doing you need to make sure the voltage is sensed the same as the inverter sees it as it will compensate based on that. What the battery sees, is checked at the battery.

Booster, you know how it works when you recharge a battery. What is the relation between the tension and the current? Does it works like a normal load except that is (probably) not linear?

So if you "inject" current but the battery doesn't accept it, the battery voltage increase accordingly?

[mkguitar]

when you "see" 15.5 volts- what current ( amps) is being passed?


Mike

[Yoshimura]

Originally Posted by mkguitar

when you "see" 15.5 volts- what current ( amps) is being passed?


Mike

Good question! I will try to monitor it.

Here's a video of the initial voltage (when I turn the inverter / charger on).

[booster]

Originally Posted by Yoshimura

Booster, you know how it works when you recharge a battery. What is the relation between the tension and the current? Does it works like a normal load except that is (probably) not linear?

So if you "inject" current but the battery doesn't accept it, the battery voltage increase accordingly?

The voltage should only rise to the setpoint of the charge source as the acceptance of the battery in amps goes down. It should be able to go to zero amps and voltage hold at the setpoint voltage, which will usually be about 14.4v for absorption and 13.5v for float on lead acid batteries.

[Yoshimura]

Originally Posted by booster

The voltage should only rise to the setpoint of the charge source as the acceptance of the battery in amps goes down. It should be able to go to zero amps and voltage hold at the setpoint voltage, which will usually be about 14.4v for absorption and 13.5v for float on lead acid batteries.

So to rise to 15.5V, either the charger setpoint is incorrect or either the battery can't accept initial current, right?

I said initial current because from the documentation, it seems that the charger start in bulk mode (constant current).

"if AC input is applied then the charger will run at full operating charging current in constant current (CC) mode until the charger reaches the boost voltage."

So the charger start in bulk mode, the battery can't accept the current, voltage jumps to 15.5V, charger notice the high voltage and then switch to absorption?

[booster]

Originally Posted by Yoshimura

So to rise to 15.5V, either the charger setpoint is incorrect or either the battery can't accept initial current, right?

I said initial current because from the documentation, it seems that the charger start in bulk mode (constant current).

"if AC input is applied then the charger will run at full operating charging current in constant current (CC) mode until the charger reaches the boost voltage."

So the charger start in bulk mode, the battery can't accept the current, voltage jumps to 15.5V, charger notice the high voltage and then switch to absorption?

That is basically correct, except the charger should never jump up above the setpoint voltage for absorption unless they are doing some kind of funny add on cycle, which I doubt. Can't say exactly for your model, but it would be typical for a charger to turn on and then check the battery voltage. If the voltage is fairly high, like above 12.6v or so, the charger would go directly to float at about 13.5v. If the voltage is lower, it will go into bulk (constant current mode) and will charge at whatever voltage it can maintain at full amps out until the amps accepted drop low enough to get to absorption voltage. It will then hold that voltage until the end of charging which will be at very low amps.

[mkguitar]

Originally Posted by Yoshimura

Good question! I will try to monitor it.

I ask as I sometimes see readings on my meters ( on various circuits) which are spurious as there are "volts" but the current is negligible.

I've found "DC voltage" on circuits which should only have AC...and when further investigated the current is in milliamps


Mike

[booster]

Originally Posted by mkguitar

I ask as I sometimes see readings on my meters ( on various circuits) which are spurious as there are "volts" but the current is negligible.

I've found "DC voltage" on circuits which should only have AC...and when further investigated the current is in milliamps


Mike

It is very common to see AC on a DC line even when running full current in the form of ripple. It is hard on stuff as it is continuous voltage spikes, so it is always trying to be minimized. Alternators, chargers, etc all have some ripple. Residual DC on and off, basically, AC or DC circuit could be anything. Discharging components, induced current, etc.


But when a charger on DC spikes to 15.5v that you see on a meter, it may have gone considerably higher for a short time that the meter missed, and even the 15.5v is worrisome for components. That is why they always say to disconnect the batteries to equalize and limit the temp correction max allowed voltages.

[Yoshimura]

Originally Posted by booster

Can't say exactly for your model, but it would be typical for a charger to turn on and then check the battery voltage. If the voltage is fairly high, like above 12.6v or so, the charger would go directly to float at about 13.5v.

It seems my charger doesn't do this!

I connected the charger to another battery. I don't know how much charged the battery is but charger was now in float mode. I turn off the charger and before the voltage could drop below 13V, I turn on the charger and the voltage went to 14.9V before dropping to 14.4V (which seems to be charger absorption voltage).

I will make sure that this battery is fully charged and then check if the voltage also jumps to 15.5V.

[Yoshimura]

Originally Posted by Yoshimura

It seems my charger doesn't do this!

I connected the charger to another battery. I don't know how much charged the battery is but charger was now in float mode. I turn off the charger and before the voltage could drop below 13V, I turn on the charger and the voltage went to 14.9V before dropping to 14.4V (which seems to be charger absorption voltage).

I will make sure that this battery is fully charged and then check if the voltage also jumps to 15.5V.

Here's the current.

[Yoshimura]

I retried this morning with the second battery (it was left on the charger all night) and measured same tension / voltage. Voltage jumps to 14.9V and rapidly drop to 14.4V.

So I reconnected my original battery and again, voltage jumped to 15.5V. I logged current and as the voltage, you can see current is all over the place. Like if the charger had a hard time regulating voltage/current with that battery.

[booster]

Originally Posted by Yoshimura

I retried this morning with the second battery (it was left on the charger all night) and measured same tension / voltage. Voltage jumps to 14.9V and rapidly drop to 14.4V.

So I reconnected my original battery and again, voltage jumped to 15.5V. I logged current and as the voltage, you can see current is all over the place. Like if the charger had a hard time regulating voltage/current with that battery.

The first low section is probably while it is evaluating the battery charge status and deciding what do.


Then it looks like it might be a typical soft start depending on the time it takes.


But if certainly goes to a big overvoltage.


Probably time to show that to manufacturer again and now it is is on two batteries.

[Yoshimura]

Originally Posted by booster

The first low section is probably while it is evaluating the battery charge status and deciding what do.

The first samples are before I turned on the inverter. I probably forget to zeroed the clamp meter.

With the test battery, I observed that the voltage rapidly went to 14.9V, stayed there for less than a second and then dropped steadily and rapidly to 14.4V with almost no undershoot. Then is stayed at 14.4V with no variation. I don't know if 14.9V is too high but the voltage seemed well controlled.

With my coach battery, the voltage goes rapidly to over 15V and you can see it oscillate (For example: 15.5V, 15.0, 15.3V). Then it drop to 14.4V but again, you see large oscillation as it drops. Finally, when it reach 14.4V, voltage still oscillate.

I don't know if you saw it but here the video for the coach battery.

Again, I don't know if the 14.9V is too high (when using the test battery) but behaviour seems different with the two batteries.

[booster]

Originally Posted by Yoshimura

The first samples are before I turned on the inverter. I probably forget to zeroed the clamp meter.

With the test battery, I observed that the voltage rapidly went to 14.9V, stayed there for less than a second and then dropped steadily and rapidly to 14.4V with almost no undershoot. Then is stayed at 14.4V with no variation. I don't know if 14.9V is too high but the voltage seemed well controlled.

With my coach battery, the voltage goes rapidly to over 15V and you can see it oscillate (For example: 15.5V, 15.0, 15.3V). Then it drop to 14.4V but again, you see large oscillation as it drops. Finally, when it reach 14.4V, voltage still oscillate.

I don't know if you saw it but here the video for the coach battery.

Again, I don't know if the 14.9V is too high (when using the test battery) but behaviour seems different with the two batteries.

14.9v would not be a big deal for most systems. If that isn't a soft start, then a very short, moderate spike is probably to be expected.


Our Magnum probably takes close to a minute to get to absorption once we plug in as it does a battery test, and then slowly ramps up the voltage over time, so is very gentle on stuff with no overshoot.