what amp rating for a split charge relay??

Post by **chimp** » 23 Jun 2006, 15:31

hey

im lookin to pop a really simple split charge second battery affair in my van (t25 1989 1.6 diesel)

now iv read all the posts/wiki guides but i still have one last question

im intending to run a couple of those cheapo cold cathode tubes, a 300w invertor and a 12v socket for chargers etc. the leisure battery will be between 85-110amp

do i need to buy a heavy duty kit with a 100amp relay such as this

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... %3AIT&rd=1

or would this be suitable

http://cgi.ebay.co.uk/12V-Split-Charge- ... dZViewItem

i originally thought the relay would have to match the second batterys ampage (which the guy selling agreed with) but am i right in thinking that unless i fit a beefier alternator the larger rated relay wont be needed.

i dont mind buying whats right (i am skint though) but i dont want to buy what i dont need!

any advice would be welcome

thanks

chris

Post by **Horza** » 23 Jun 2006, 15:34

30 amp I believe is the norm. It's the charging current that the battery draws you are interested in, not the rated Amp hours.

Website · Post by **dbroada** » 23 Jun 2006, 15:46

The good news is that in MOST cases a 30 or 40 Amp relay from a breakers (or about £5 from Halfords) will be good enough.

You don't have an 80 Amp battery, you have an 80 Amp Hour battery. In simple terms (not totally acurate but good enough for this) you can power an 80Amp device for 1 hour or a 1 Amp device for 80 hours.

While it would appear that you can't use more than the alternator gives you do get higher currents if yur batteries are at different states of charge. If there is a large discrepancy the more charged battery will try to charge the flatter one - and this can be LOTS of amps. When this happens one of your fuses will blow.

I would start with a 30/40 amp relay fused at 25 Amp (wired in 6mm / 50Amp cable) and see if it works for you. (Mine does). If you keep blowing fuses you will have to look at increasing cable size & fuses as well as relay. If that doesn't solve it you might consider some diodes instead (This is NOT a cheap option (yet))

Post by **"WEAZLECHIN"** » 23 Jun 2006, 20:50

euan is right. westys have a 30a. i just got a 40a 5 pole off ebay £2, fitted it, and all is good.

Post by **chimp** » 24 Jun 2006, 14:32

thanks guys!

thats what i though, just wasnt sure. you've saved me some money there, can go for the beefier batt now.

thanks