Permanent trickle charger for starter battery?

Wrinkledpants

2017 144WB 4x4
We have a 15A shore plug in the front bumper that feeds our lithium system in the rear of the van. Is there anyway to tap into this for a permanent trickle charger on the starter battery? We occasionally go a few weeks to a month between usage, and it seems prudent to keep the starter battery on a trickle charger. Would love it if we could tap that single plug in up front for this.
 

HarryN

Well-known member
Some people will just use a <10 watt panel in the wind shield to keep the starter battery trickle charged.

In theory you could run a trickle charger off of the house batteries to the starter battery - something like a ctek battery to battery charger.
 

Wrinkledpants

2017 144WB 4x4
This is parked inside - plus no desire to store or deal with a portable panel. A B2B charger off the house battery could work.
 

Midwestdrifter

Engineer In Residence
I would just pick up a 13.3V single voltage float charger. Something in the 500mA to 1A range. No logic needed, its just to keep the battery from draining during storage. You could easily hardwire it in.

Does your aux bank share a ground with the starter? Then you can use one of these mini Dc-DC chargers to keep the starter topped of. This assumes the aux bank is being kept charged though.

https://www.lslproducts.net/TLSPage.html
 
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Shawn182

Well-known member
IF your rig typically stays plugged in via the 15A shore power, just add a small 110V smart battery charger on the starer battery.
 

Wrinkledpants

2017 144WB 4x4
Yeah - the only time we'd want to use it is when it's parked. Anytime it's parked, it's plugged in to keep the fridge going. Sometimes it's parked for a day, sometimes 3-weeks. No need to have the charger going any other time other than parked and plugged in - hence the desire for using that 15A plug up front.
 

john61ct

Active member
Did not read the thread.

Yes, at the "12V" nominal output, add a little "echo-charge" unit from Xantrex. Used to be Heart, unchanged from the acquisition.

Like a DCDC, one way only so can't drain Starter ever.

Like an ACR, only joins Starter to House while charge source is active

steps voltage down a little, cannot output over 14.4V

limited to 15A current even if target batt tries to pull more

Can be found on eBay under $100, very robust

New maybe $150.
 

john61ct

Active member
The advantage of a DC-input device, is it continues to work when charging House from any other source, not just from your shore charger.
 

sipma02

Currently full time in the van
Did not read the thread.

Yes, at the "12V" nominal output, add a little "echo-charge" unit from Xantrex. Used to be Heart, unchanged from the acquisition.

Like a DCDC, one way only so can't drain Starter ever.

Like an ACR, only joins Starter to House while charge source is active

steps voltage down a little, cannot output over 14.4V

limited to 15A current even if target batt tries to pull more

Can be found on eBay under $100, very robust

New maybe $150.
I'm still learning about the optimal setup for my application. This is interesting! So basically, this would connect + charge the house batteries to the starter battery, only when they're being charged by the solar setup? That way, the starter battery would receive extra charge from the house batteries when the vehicle is sitting for an extended period. (assuming its outside/receiving solar charge)
 

Skippy and Emu

Active member
I would just pick up a 13.3V single voltage float charger. Something in the 500mA to 1A range. No logic needed, its just to keep the battery from draining during storage. You could easily hardwire it in.

Does your aux bank share a ground with the starter? Then you can use one of these mini Dc-DC chargers to keep the starter topped of. This assumes the aux bank is being kept charged though.

https://www.lslproducts.net/TLSPage.html
The OP stated that the "house" batteries were Lithium.
In this case, Revision G2 model of this brand of charger will be required, as it has an adjustable trigger threshold to cater for the higher resting voltage of Lithium.

In my case, I have a Sterling Battery Maintainer. It worked well with the old AGM Gel setup. It no longer works as intended, with my recently installed Lithium setup. It has a fixed trigger threshold of 13.3v. This is too high for my setup. The Sterling " thinks" the batteries are being charged, and therefore, falsely allows current to the " start " battery. I haven't got around to finding a solution yet, but am thinking of perhaps putting a silicon diode in series with the input to the Sterling. The anticipated approx. 0.7v volt drop, may be just enough to be below the trigger threshold. Any other thoughts or ideas on this, are more than welcome!
 

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john61ct

Active member
So basically, this would connect + charge the house batteries to the starter battery, only when they're being charged by the solar setup?
Designed to go **from** the House bank circuit to Starter, one way only.

Triggered closed by voltage going high, IOW connects when **any** DC charge source is active, so yes to solar, yes to shore or genset charging, you could even wire an alternator output if appropriate.

So House gets [Full charge minus what Starter batt needs (up to 15A)] and that Starter input is voltage following less about half a volt.

Which is fine for a Starter in normal use, but not suitable to turn in the other direction targeting a fussy/expensive House bank.

A DC-DC charger might be a **little** better since it delivers a separately filtered 3-stage output, but that is usually more expensive, and a cheap Starter rarely gets coddled like that.

An ACR/VSR would not drop voltage as much, would not limit current, and usually allows 2-way flow in either direction, high-voltage sensing trigger from either side.

> That way, the starter battery would receive extra charge from the house batteries when the vehicle is sitting for an extended period. (assuming its outside/receiving solar charge)

Yes, as with any of those three device types.
 

john61ct

Active member
In my case, I have a Sterling Battery Maintainer. It worked well with the old AGM Gel setup. It no longer works as intended, with my recently installed Lithium setup. It has a fixed trigger threshold of 13.3v. This is too high for my setup. The Sterling " thinks" the batteries are being charged, and therefore, falsely allows current to the " start " battery
Actually there is no harm in Starter drawing the "surface charge" off LFP a little bit after the charge source stops.

Amps drawn will be very low, plus

13.3V is actually within 0.02 per cell of resting Full with 4S LFP

so any significant load will drop the circuit voltage below the setpoint and isolate starter.

Don't kludge a diode, V drop will vary with current, less predictable result for solving a non problem.

Just observe a couple cycles with a DMM and ammeter, could even hard wire cheap ones.
 

Skippy and Emu

Active member
Actually there is no harm in Starter drawing the "surface charge" off LFP a little bit after the charge source stops.

Amps drawn will be very low, plus

13.3V is actually within 0.02 per cell of resting Full with 4S LFP

so any significant load will drop the circuit voltage below the setpoint and isolate starter.

Don't kludge a diode, V drop will vary with current, less predictable result for solving a non problem.

Just observe a couple cycles with a DMM and ammeter, could even hard wire cheap ones.
Thank you for your input.
Further info for consideration.
I have just been through 14 days isolation, after I crossed the West Australia / South Australia border.
So, upon arriving home, the start and house batteries were both effectively fully charged. When at home, the Sprinter resides undercover in my shed. With the lithium batteries, I no longer connect to shore power, as I used to do with the Gels. After 14 days, the Lithiums were down to 56%. The Sterling was still happily "maintaining " the Start battery. At this stage, I switched the Master cutoff switch to shut the whole system down. The Lithiums were reading 13.2v. I believe the Sterling cut out point is 12.9v. I measured the parasitic current draw, before, I shut the system down. It was approx. 600ma. This would consist of whatever the Sterling was drawing, aftermarket security alarm, GPS tracker, OEM Sprinter electronics, Lithium circuitry ( BMS and Bluetooth ) and the electronic low battery cutout. I think the Sterling would have kept drawing current, probably until the low votage cut out kicked in. The Sterling can only supply a maximum of 3 amps. Therefore, I think the small current variation would not significantly alter an expected 0.7v diode volt drop. I have not tried it yet !
 

john61ct

Active member
Can you link to that specific Sterling model?

After 14 days, the Lithiums were down to 56%. The Sterling was still happily "maintaining " the Start battery.
That is a fair parasitic draw!

I would never leave the Sterling on while parked, why not take advantage of its built-in VSR?

And in fact IMO the LFP should be left at 30-40% and fully isolated (master **bank** switch) when the rig is not being closely monitored.

Leave a cheap lead batt powering the parasites if necessary, or shut everything off.
 

Skippy and Emu

Active member
Can you link to that specific Sterling model?
https://www.sterling-power-usa.com/sterling-power-usa12vto12vbatterymaintainer.aspx

Quote:
Originally Posted by Skippy and Emu View Post
After 14 days, the Lithiums were down to 56%. The Sterling was still happily "maintaining " the Start battery.
End Quote:

That is a fair parasitic draw!
Agreed !

I would never leave the Sterling on while parked, why not take advantage of its built-in VSR?
?

And in fact IMO the LFP should be left at 30-40% and fully isolated (master **bank** switch) when the rig is not being closely monitored.
I think 50 - 60% is the recommended figure from the battery Manufacturer in my case.
Yes, I use the Master cut off switch. Rather inconvenient though. Was hoping I could get away with just not connecting to shore power.


Leave a cheap lead batt powering the parasites if necessary, or shut everything off.
Not a bad idea. The pararsites must be fed !
I do have already installed, a totally separate, stand alone battery system ( 100ah Gel ) It has it's own 100w solar panel and dc-dc charger setup. I could plug it into shore power when the Sprinter is in the shed. Would not be overly difficult to rewire the Sterling to run off the Baintech.
Thanks for the idea !
 

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john61ct

Active member
Note I meant a "bank Master" isolation switch, for the LFP bank only

not a system wide one.

That Sterling is designed to go from Starter to House, everything being lead chemistry FYI.

It is triggered to start at 100% Full resting for LFP, and only isolates itself (VSR) at 12.9, which should be well over 50% SoC.

Which happens to be a good storage point for LFP, so long as no further parasites are connected.

As to protecting the lead side, whether the feed which loads etc

left as an exercise for the reader, at least for now.

Either connecting to shore power, or shutting down the parasites is likely necessary.

A third bank, with solar, starts to get more complicated, but so long as the LFP is protected, go for it, lead is cheap.

OTH lead's life is greatly shortened if not mostly kept at 100% Full, and GEL can be tricky to get right.
 
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