Camper battery charging rate

[Ashes]

I'm looking to upgrade my sc40 traxide isolator to a usi160 so I can charge my camper battery via a rear anderson plug both on the move and while camped. The sc40 won't charge more than the 2nd car battery without tripping the circuit breaker.
If I am free camped for a few days, how effective would the alternator be at recharging the Optima 2nd battery in the car and a 130ah battery in the camper by running the car on idle? I have a solar setup but need a plan B for extended bad solar days.

[Vern]

Will take ages at idle. Better off setting the solar up when you set up camp(to charge the 130ah), I do this and it works fine, that's with a 105ah second battery in the car, and two 105ah batteries in the camper.

[Tombie]

And will glaze (and ultimately damage) your engine.

[Ashes]

Thanks Tombie..I think...
Hoping you or another electrickery expert can explain this in a bit more detail and perhaps break it down into the following for the non mechanical like myself and many others i'm sure who would benefit from this.

- what specifically is the glazing you are talking about and does it affect petrol and diesel engines the same way
- is it bad to just charge a cranking battery in this manner when it is running low?
- is it bad to idle charge a main and 2nd battery in this manner (with a traxide isolator in between) or is the only safe option to actually go for a drive with higher revs every day or so? I run a fridge off the 2nd car battery when camping or touring) and it runs low after a couple of days in warm weather if the car isnt being used.
- I know this is a piece of string length question but how long does it take to mostly fully charge a 2nd battery Optima Yellow top from say 50% (at idle compared to the car moving) (are we talking minutes or hours..)?
- Are there smarts in the car that reduce the alternator output for idling vs moving?
- Is it wise to have a connection between the 2nd battery and camper battery to give a overall higher battery capacity and also effectively balance the voltages while camped? I have been doing this so I can feed Solar back into both the camper battery and car batteries.

Sorry for all the questions....but it would help me understand this a lot better

[Vern]

Its bad for the engine to let it idle for long periods of time, it glazes the bores!
It also takes hours to charge a second battery whilst driving. Do you have the ability to charge the second battery from your solar? Also what output it is your solar panel?

[Ashes]

I have a 120w panel which should be enough to keep up with my 12v needs unless I have a extended run of bad solar days. I can connect the camper and car aux battery via a 8b&s extension cable and my regulator is on the camper.

[drivesafe]

Hi Ashes and as above, long term idling is not good for your motor but I will leave the mechanical specifics of this to other in that field.

From an electrical aspect, most new vehicles have large alternators. These large alternators are NOT there to help us charge batteries.

The reason for large alternators is for the vehicle to be able to generate enough energy at idle to cover the vehicle’s own electrical requirements.

It works something like this.

If a vehicle needs a minimum of say 40 amps at idle, a not uncommon amount of power for new vehicles, like D3s and D4s, then an alternator size is needed that will produce that amount of energy at low revs.

This means for an alternator put out 50 amps at say 700 RPM, you need one with an output 140 amps at say 1500 to 2000 RPM.

So at idle, you will have very little if any surplus energy available for charging batteries.

But take the vehicle for a one hour drive and you will replace as much used battery capacity as it would take an idling engine to do in at least 5 hours.

Now Ashes, in your case, where as you posted above, you have discharged your two batteries ( Calcium/Calcium ( Ca/Ca ) cranking battery and Optima Spiral Wound AGM auxiliary battery ) down to 50%, a one hour drive will bring your cranking battery back up to around 80% and your Optima auxiliary battery to well over 90%.

An hour and a half drive will near fully charge your Optima and bring your cranking battery to around the 90%.

So a one hour drive is the most beneficial.

Now to put this another way. Idling for one hour will replace, at VERY best, 10 amp hours ( Ah ) of used battery capacity spread over the two batteries.

A one hour drive will replace about 27 amp hours in the cranking battery and at least 22 amp hours in the Optima.

Note, because an Optima is a rapid charge battery, if your were to discharge the Optima down to 20% and then do your one hour drive, you would still charge it back up around 90% but you will now have replaced 33 amp hours of used battery capacity.

So this would mean a maximum of 10Ah replacement for a one hour idle verses at least 60Ah for a one hour drive.

Hope this helps!

[josh.huber]

Honda eu20 generator and a ctek 25amp

[Melbourne Park]

Honda eu20 generator and a ctek 25amp

What is a ctek 25amp?

The small honda generators are designed for 240 volt capacity. If the trailer has a 240V input and a charging controller for when on 240 volts mains power, then the Honda is likely a good solution. I have an eu20 and its output is indicated at around a 25 amps when charging van batteries via the 240 volt mains input into the van. I had two 130 AH AGM batteries at around half capacity used, the Honda charged them up to capacity in under 4 hours. I haven't done the maths to work all that out though ...

I have 300 Watt panels for the two van batteries. They keep the fridge going in the Melbourne winter, but cloud is a killer, but only if the van's fridge is not set on maximum. Beware of maximum fridge settings!!!

There is a Sydney company who sells a 12 V Honda powered unit that has an Australian made Bosch alternator on it, and it charges 12 volt batteries very efficiently. I think they sell for around $1,400 retail. With a 5 year warranty I think... the maker is Christie Engineering, based in Sydney. Their cheapest unit is I think a 12V 80AMP battery charger.
I presume it would be noisier by quite a bit that a Honda 240 20 unit, although the Christie uses a Honda motor too. Two batteries it would be a better setup probably but for the weight.


The Honda generator is much cheaper, but its designed for 240 volts and its ampage with 12V is only 8, unlike the Sydney company's unit 12v alternator unit.

[Tombie]

I have an eu20 and its output is indicated at around a 25 amps when charging van batteries via the 240 volt mains input into the van. I had two 130 AH AGM batteries at around half capacity used, the Honda charged them up to capacity in under 4 hours. I haven't done the maths to work all that out though ...

Correct... Because it doesn't add up

2x130 = 260 at 50% = 130ah required, 4 hrs @ 25ah = 100ah -> 30ah deficit

Not to mention that last few percent in a battery take a bit longer to "push" in...

Although your Solar may have injected a little bit in