# Charging secondary batteries from van alternator



## 89043 (May 12, 2005)

Outfitting a VW transporter as RV. Researching secondary battery charging (ca 200 Ah deep cycle). Known facts on car alternator secondary batteries charge only up to ca 80%. This forces me to carry some 200Ah to have 60 Ah available. Hookup to 220 V is no issue as we camp wild. Generator neither as we want not to be a nuisance.

Found on the web Sterling Power Products www.sterling-power.com sell what they call a battery to Battery charger, what allows complete charging of the 2nd battery from the car alternator.

Anyone who has experience with this gear?
Anyone who has an other solution to get the 2nd battery full on alternator?
Looking forward to hear from you


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## autostratus (May 9, 2005)

Have you looked at the website for self builders www.sbmcc.co.uk which might be useful to you.

I'm surprised George hasn't contributed to your threads, perhaps he's away at the moment.


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## spykal (May 9, 2005)

Hi

have a look at this web site too, for information :

http://www.victronenergy.com/

I see you have posted a separate message about this, really it's best to keep all your posts in one thread if you don't want to confuse us :lol:

Mike

P.S. and Gillian was right ...George may be along in a minute ...he will help sort you out.


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## DABurleigh (May 9, 2005)

archimedes,

I don't know where your 60Ah comes from. Yes, at least someone on this site has a Sterling battery-to-battery charger; have a search and read of the archives. Check whether the output is as high as you want; if not, Sterling also do an alternator to battery charger with higher output that does not need a wiring connection internal to the alternator.

Going up from ~80% capacity is not without its penalties in terms of equipment cost, battery life and topping-up requirements. I initially was attracted to going down the same lines as you are suggesting, but in the end decided to keep to industry-standard and widely accepted forms of charging both from my battery-safe mains charging from a Victron inverter/charger/UPS as well as a heavy duty (but standard) alternator linked to the leisure batteries with thick welding cable via a heavy duty split charge relay (and then on to the inverter).

Having similar terminal charging voltages for the vehicle and leisure batteries via both mains and alternator charging also avoids wierd, albeit minor, effects such as the leisure battery losing charge to the vehicle battery through the relay.

Dave


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## 89043 (May 12, 2005)

*reply to DAVE summarizing tech parts of replies over PM*

FIrst of all thanks for the info. Looking for the archives did not find any. Will have a second look.
And than some answers to your questions,

Well the 60 Ah come from the A and utilization time table corrected for efficiency etc, part of the gear is 220V and to be run over an inverter, either Victron or Stuber.
Actually I need the 60 VA in the evening for video, photo and text editing plus communications and charging of the camera batteries, we will minimise on the consumption for lighting, and already went away from the first planned in diesel based heater to gas heating, but even that and the other "phantom" loads from peltier cooler to the alarm.
Having anyhow that 60 VA need we will use it in part at noon for reheating meals. As we work out a combined dinner table - kitchen block - office desk , an open gas ring is not first choice. We will test a Microwave as that would minimise time and keep low odours. Less cooking water for drinks, water heating is not planned in, less a trifle for washing dishes (again an advantage of the MW, no pans and pots to wash) The electricity used at noon will be replenished anyhow by afternoon driving.

The 200 Ah come from conservative rating what can be got from batteries charged from the alternator along with the starter battery using a relay type battery separator, most probably a microprocessor controlled Cyrix. 
Batteries for the supply will be semi traction or traction. 
The calculus for the 200 Ah is unsophisticated, Without some charging management given the 14.2 -14.4 V of the alternator the supply batteries will get at best ca 8O % charged. To keep an acceptable service life for the batteries 50% discharge is imposed as the lower limit. Makes that to get the 60 Ah that will come from 30 % of the installed capacity based on the C/5. As batteries are physical units and I preferred to have two 6 V in series 200 Ah is the projected capacity.
Althoug we will opt for a combined charger /inverter and so will have the possibility to restore battery capacity "once in a while" the possibility to recharge daily from the grid is nihil. 
I am well aware that getting VA in over the 80 % does not come free. The Stirling is not precisely cheap hardware, but in principle if the right charging curve is applied battery life should not suffer (one reason to ask users about their experience with the Stirling or other, meanwhile I found out that Balmar has similar gear under the name Digital Duo Charge) Topping up of the batteries should not be excessive if the charging curve is OK and charging not driven into the gassing region.

The advantage I am afther is that charge above 80 say to 90 or at the limit 95 would supply more "fast" power from the batteries. I do not want to increase the installed battery base beyond those 200 Ah as well for weight as for the required footprint. Additional battery capacity is not free either

As for the alternator, there I go for the largest that can be fitter standard a 140A 12V. Due to the regulation setup of the VW transporter non-standard is not advised as it voids the vans warranty. Same goes for the charger amplifier from Stirling. Although there is no wiring internally in the regulator there is extensive change in the wiring around the alternator. That one has to remain wired directly to the VW's starter positive stud not to have problems. Attaching heavy gauge wire to that stud with an inline fuse at one end and "some gear" preferably over a battery switch is as far as I can go if I want uncle "Wolfsburg" from cursing me.

So sofar a bit more about the "draft" of the project, thanks for the info and looking forward to any more info you can share.

Marcel


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## 88724 (May 9, 2005)

Hi Marcel

You would be lucky to put 70% into batteries via an alternator alone.

For invertors I would look at Sterling the 2 you mention make very good Quality products BUT the rating on the box is not the continuous rating at 40 degrees, with Sterling if you buy an 1800 w invertor that invertor will run 24/7 at 1800w

Check out the true ratings for Victron what you will Find is that the Advertised figure at least 25% less ie a 1600w is VA rather than "Real" watts (it will take to long to explain but it means your being short changed its power factor rather than actual watts) and this is at 25 degrees rather than 40, the reality is that a 1600w Victron is only 1200w when rated as per the Sterling (and how invertors have to be rated in USA, acurately and all using same method)

George


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## 89043 (May 12, 2005)

*THanks*

Thanks George,

I had also remarked the "slide" in the data of Victron. No need to explain me the long stuff: I am an engineer so cos phi is no latin to me.

Problem with Stirling power is that it looks as if he has no representative in Belgium, or maybe even not on the continent. I send him an email to enquire about that but sofar no answer.

You say the two you mention are good products. The two... do you mean the Stirling and the Balmar or the two Stirling items?

As for inverters locally in Belgium if I keep it to the more professional gear three brans have local outlets, Stuber , Victron and Mastervolt, - Stirling is not on our market as said. Will look into the inverter once I have solved the problem of DC supply although am listing info and definite questions about the conversion stage.
The principle of wiring in the second battery chain as an appliance on the primary chain is common on the Balmar and the Stirling approach. The latter seems more flexible. Any idea what the prolonged activity of the starter battery at 13V, does for the lifetime of that one? Is equivalent of course to driving with the full lights on and electrical heater in winter blazing on a standard alternator. Will have also to make out if as I intend to do have instead of the 100A one I get a 140 A what regulation will do, I presume the starter battery will charge up, rise in voltage and then dissipates current to the secondary chain along with the alternator current.

Want to have your idea about an approach, part experimental, part workaround: What if I wired (with adequate gauge wire of course) a the secondary batteries over a battery separator relay in the classical way but with a battery switch mounted that can switch the secondary battery shunting out the separator once the current to the secondary battery levels off.

Marcel


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## 88724 (May 9, 2005)

Hi Marcel

The email side is bad I hear, everybody moans about it, I never tried it, I have always dealt with them via Phone.

Stuber, Victron and Sterling are all good well made products, I meant that the two that you mention are Good well made products.

The Sterling battery to battery charger as far as I am aware doesnt leave the starter on 13v long term, I can see what you mean about the voltage being pulled down, but can only imagine that some kind of control is in place to avoid it. (otherwise the product would be causing problems and would hazard a guess that as the product is still sold its not causing any probs with starter batteryside)

I dont understand why you would want to take control of the output with a switch and relay, of course yu could do it, but I cannot see any benefit.

George


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